PROPOSAL

for a Silicon Vertex Tracker (VTX)

for the PHENIX Experiment

**Proposal for a Silicon Vertex Tracker (VTX) for the PHENIX
Experiment**

M. Baker, R. Nouicer, R. Pak, P. Steinberg

Brookhaven National Laboratory, Chemistry Department, Upton, NY
11973-5000, USA

Z. Li

Brookhaven National Laboratory, Instrumentation Division, Upton, NY
11973-5000, USA

J.S. Haggerty, J.T. Mitchel, C.L. Woody

Brookhaven National Laboratory, Physics Department, Upton, NY
11973-5000, USA

A.D. Frawley

Florida State University, Tallahassee, FL 32306, USA

J. Crandall, J.C. Hill, J.G. Lajoie, C.A. Ogilvie, H. Pei, J. Rak,
G.Skank, S. Skutnik,

G. Sleege, G. Tuttle

Iowa State University, Ames, IA 56011, USA

M. Tanaka

High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki
305-0801, Japan.

N. Saito, M. Togawa, M. Wagner

Kyoto University, Kyoto 606, Japan

H.W. van Hecke, G.J. Kunde, D.M. Lee, M. J. Leitch, P.L. McGaughey, W.E.
Sondheim

Los Alamos National Laboratory, Los Alamos, NM 87545, USA

T. Kawasaki, K. Fujiwara

Niigata University, Niigata 950-2181, Japan

T.C. Awes, M. Bobrek, C.L. Britton, W.L. Bryan, K.N. Castleberry, V.
Cianciolo,

Y.V. Efremenko, K.F. Read, D.O. Silvermyr, P.W. Stankus, A.L.
Wintenberg, G.R. Young

Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

Y. Akiba, H. En'yo, Y. Goto, J.M. Heuser, H. Kano, H. Ohnishi, V. Rykov,
T. Tabaru, K.Tanida, J. Tojo

RIKEN (The Institute of Physical and Chemical Research,) Wako, Saitama
351-0198, Japan

S. Abeytunge, R. Averbeck, A. Deshpande , A. Dion, A. Drees, T.K.
Hemmick, B.V. Jacak, C. Pancake, V.S. Pantuev, D. Walker

Stony Brook University, Department of Physics and Astronomy, Stony
Brook, NY 11794, USA

B. Bassalleck, D.E. Fields, M. Malik

University of New Mexico, Albuquerque, NM, USA

[1. Executive Summary 1](#executive-summary)

[2. Physics Overview 4](#physics-overview)

[2.1 Probes of Early, Highest Energy-Density Stage of Heavy-ion
Reactions
4](#probes-of-early-highest-energy-density-stage-of-heavy-ion-reactions)

[Potential enhancement of open charm production
5](#potential-enhancement-of-open-charm-production)

[Open Beauty Production 6](#open-beauty-production)

[Ratio of charm and beauty production and its centrality dependence
7](#ratio-of-charm-and-beauty-production-and-its-centrality-dependence)

[Energy-loss of heavy-quarks 7](#energy-loss-of-heavy-quarks)

[Open charm reference to J/ suppression and enhancement
9](#open-charm-reference-to-j-suppression-and-enhancement)

[Open beauty and J/suppression 10](#open-beauty-and-jsuppression)

[Thermal di-lepton and open charm 11](#thermal-di-lepton-and-open-charm)

[High *p*~T~ phenomena with light flavor in 10 -- 15 GeV/c in *p*~T~
12](#high-pt-phenomena-with-light-flavor-in-10-15-gevc-in-pt)

[Measurement of Upsilon states 12](#measurement-of-upsilon-states)

[2.2 Determination of spin structure of nucleon.
12](#determination-of-spin-structure-of-nucleon.)

[Exploring the spin structure of the nucleon: The past
12](#exploring-the-spin-structure-of-the-nucleon-the-past)

[Gluon polarization measurement at RHIC:
13](#gluon-polarization-measurement-at-rhic)

[The role of Silicon Vertex Detector:
14](#the-role-of-silicon-vertex-detector)

[The heavy quark physics (open charm and beauty production)
15](#the-heavy-quark-physics-open-charm-and-beauty-production)

[Direct photon + Jet measurement: 17](#direct-photon-jet-measurement)

[Other advantages of the Silicon Vertex Detector:
17](#other-advantages-of-the-silicon-vertex-detector)

[2.3 Exploration of the nucleon structure in nuclei
18](#exploration-of-the-nucleon-structure-in-nuclei)

[3. Physics measurements with the VTX detector
23](#physics-measurements-with-the-vtx-detector)

[3.1 Design Considerations and the VTX detector geometry
23](#design-considerations-and-the-vtx-detector-geometry)

[Design Considerations 23](#design-considerations)

[VTX detector geometry 24](#vtx-detector-geometry)

[Detector Occupancy 25](#detector-occupancy)

[Central Track -- VTX matching 26](#central-track-vtx-matching)

[3.2 Open Charm and Beauty Measurement
28](#open-charm-and-beauty-measurement)

[Open Charm measurement from semi-leptonic decay
28](#open-charm-measurement-from-semi-leptonic-decay)

[Direct Measurement of *D^0^K^-+^* at high *p~T~*
30](#direct-measurement-of-d0k--at-high-pt)

[Open Beauty Measurement 33](#open-beauty-measurement)

[3.3 Photon and jets measurement in polarized p+p
35](#photon-and-jets-measurement-in-polarized-pp)

[3.4 Improved momentum resolution and pt resolution
38](#improved-momentum-resolution-and-pt-resolution)

[3.5 Event rate estimates 40](#event-rate-estimates)

[4. VTX Detector system 46](#vtx-detector-system)

[4.1 Overview 46](#overview)

[4.2 Hybrid pixels 48](#hybrid-pixels)

[Sensor 49](#sensor)

[Readout chip 50](#readout-chip)

[Interconnection of Sensor and Readout Chip ("Bump Bonding")
51](#interconnection-of-sensor-and-readout-chip-bump-bonding)

[Readout Bus 53](#readout-bus)

[Pilot module 54](#pilot-module)

[Front End Modules 55](#front-end-modules)

[Pixel detectors operating in the NA60 experiment:
56](#pixel-detectors-operating-in-the-na60-experiment)

[4.3 Silicon Strip Detector 57](#silicon-strip-detector)

[Strip Sensors 58](#strip-sensors)

[Laboratory tests of the strip sensors
59](#laboratory-tests-of-the-strip-sensors)

[Sensor Prototypes in Test Beam 61](#sensor-prototypes-in-test-beam)

[The Second Prototype Sensor and Tests with SVX4 Readout Chip
64](#the-second-prototype-sensor-and-tests-with-svx4-readout-chip)

[SVX4 readout chip 65](#svx4-readout-chip)

[Sensor Readout Card (ROC) / Readout Bus
65](#sensor-readout-card-roc-readout-bus)

[Pilot Module 67](#pilot-module-1)

[Front-End Module 67](#front-end-module)

[Zero Suppression 67](#zero-suppression)

[Si strip production/testing/assembly schedule
71](#si-strip-productiontestingassembly-schedule)

[4.4 Mechanical Structure and Cooling
75](#mechanical-structure-and-cooling)

[Design Criteria 76](#design-criteria)

[Structural Support 77](#structural-support)

[Detector Ladders and Cooling 78](#detector-ladders-and-cooling)

[Radiation Length 81](#radiation-length)

[4.5 Detector integration into PHENIX
81](#detector-integration-into-phenix)

[VTX detector assembly 82](#vtx-detector-assembly)

[Error Budget 82](#error-budget)

[Ladder Assembly - pixels 82](#ladder-assembly---pixels)

[Ladder Assembly -- strips 83](#ladder-assembly-strips)

[Half detector assembly 83](#half-detector-assembly)

[Integration into PHENIX 84](#integration-into-phenix)

[DAQ 85](#daq)

[5. R&D 86](#rd)

[6. Project management and responsibilities
88](#project-management-and-responsibilities)

[6.1 Project background 88](#project-background)

[6.2 The management plan for the VTX
89](#the-management-plan-for-the-vtx)

[PHENIX management structure 89](#phenix-management-structure)

[PHENIX subsystem leadership 89](#phenix-subsystem-leadership)

[Role of BNL 90](#role-of-bnl)

[Specification of deliverables 91](#specification-of-deliverables)

[6.3 Manpower for Tasks 92](#manpower-for-tasks)

[6.4 Institutional involvement 94](#institutional-involvement)

[Brookhaven National Laboratory, Chemistry Department (BNL CHEM)
95](#brookhaven-national-laboratory-chemistry-department-bnl-chem)

[Brookhaven National Laboratory, Instrumentation Division (BNL ID)
95](#brookhaven-national-laboratory-instrumentation-division-bnl-id)

[Brookhaven National Laboratory, Physics Department (BNL PHY)
96](#brookhaven-national-laboratory-physics-department-bnl-phy)

[Iowa State University (ISU) 96](#iowa-state-university-isu)

[Kyoto University (Kyoto) 96](#kyoto-university-kyoto)

[Los Alamos National Laboratory (LANL)
97](#los-alamos-national-laboratory-lanl)

[University of New Mexico, Albuquerque (UNM)
97](#university-of-new-mexico-albuquerque-unm)

[Oak Ridge National Laboratory (ORNL)
98](#oak-ridge-national-laboratory-ornl)

[RIKEN Institute (RIKEN) 98](#riken-institute-riken)

[Stony Brook University, Physics Department (SBU)
99](#stony-brook-university-physics-department-sbu)

[6.5 Foreign contributions 99](#foreign-contributions)

[7 Budget and schedule 101](#budget-and-schedule)

[7.1 Total estimated cost (TEC) 101](#total-estimated-cost-tec)

[Fiscal Responsibilities 101](#fiscal-responsibilities)

[Contingency Analysis 101](#contingency-analysis)

[Overhead Estimate 101](#overhead-estimate)

[Budget 102](#budget)

[7.2 Schedule 105](#schedule)

[Appendix A ENDCAP Extension 110](#appendix-a-endcap-extension)

[Introduction 110](#introduction)

[A.1 Goals of the Endcap Upgrade 112](#a.1-goals-of-the-endcap-upgrade)

[A.1.1 Spin Structure of the Nucleon
112](#a.1.1-spin-structure-of-the-nucleon)

[A.1.2 Exploration of Gluon Structure in Nuclei
113](#a.1.2-exploration-of-gluon-structure-in-nuclei)

[A.1.3 Probes of Early, Highest Energy-Density Stage of Heavy-ion
Reactions
114](#a.1.3-probes-of-early-highest-energy-density-stage-of-heavy-ion-reactions)

[Energy Loss of Heavy Quarks 114](#energy-loss-of-heavy-quarks-1)

[Open Charm and Beauty Enhancement
114](#open-charm-and-beauty-enhancement)

[J/ Suppression 114](#j-suppression)

[Other Physics Topics 114](#other-physics-topics)

[A.2 Simulations and Required Performance for the Si Endcap Upgrade
115](#a.2-simulations-and-required-performance-for-the-si-endcap-upgrade)

[A.2.1 Open Charm Measurement 116](#a.2.1-open-charm-measurement)

[A.2.2 Open Beauty Measurement 118](#a.2.2-open-beauty-measurement)

[A.2.3 Trigger Plans 120](#a.2.3-trigger-plans)

[A.2.4 Si Endcap Event Rates 120](#a.2.4-si-endcap-event-rates)

[A.2.5 Matching to Muon Spectrometers
121](#a.2.5-matching-to-muon-spectrometers)

[A.2.6 Integration with PHENIX 121](#a.2.6-integration-with-phenix)

[A.3 Technical Aspects of the Proposed Endcap Vertex Detector
121](#a.3-technical-aspects-of-the-proposed-endcap-vertex-detector)

[A.3.1 Silicon Readout Chip --PHX 121](#a.3.1-silicon-readout-chip-phx)

[A.3.2 Silicon Ministrip Sensors 122](#a.3.2-silicon-ministrip-sensors)

[A.3.3 Silicon Ministrip Control Chip
125](#a.3.3-silicon-ministrip-control-chip)

[A.3.4 Mechanical Structure and Cooling
126](#a.3.4-mechanical-structure-and-cooling)

[A.3.5 Endcap Ladder Structure 126](#a.3.5-endcap-ladder-structure)

[6.3.7 Endcap Analysis Summary 128](#endcap-analysis-summary)

[A.4 R+D Schedule, Responsibilities and Budget
128](#a.4-rd-schedule-responsibilities-and-budget)

[A.4.1 Schedule 128](#a.4.1-schedule)

[A.4.2 Responsibilities 129](#a.4.2-responsibilities)

**List of Figures**

[Figure 1 Charm enhancement expected at RHIC energy from ref. 3. In both
panels, contribution from the initial gluon fusion (solid), pre-thermal
production (dot-dashed), and thermal production (dashed, lowest) are
shown. The left panel is the calculation with energy density of 3.2
GeV/fm^3^, while the right panel shows the case with energy density 4
times higher. 6](#__RefHeading___Toc66641772)

[Figure 2 Ratio of Jet Quenching factor QH/QL of heavy quark (QH) and
light quark (QL) in high density QCD medium as function of pT of the
quark, from ref. 8. The solid line is with no energy cut-off for gluon
and the dashed line is with cut off of 0.5 GeV.
8](#__RefHeading___Toc66641773)

[Figure 3 Single electron data of PHENIX compared with two extreme
models of charm *p*~T~ distribution. From ref. 12.
9](#__RefHeading___Toc66641774)

[Figure 4 The ratio of J/ yield and open charm yield predicted in ref.
10](#__RefHeading___Toc66641775)

[Figure 5 The di-electron effective mass distribution in PHENIX central
arm acceptance in central Au+Au collision at $\sqrt{s_{\text{NN}}}$= 200
GeV predicted by Rapp^19^. In the intermediate mass region (1 \< Mee \<
2.5 GeV), the dominant sources of electron pairs are open charm and
thermal radiation from the QGP and hot hadronic gas.
11](#__RefHeading___Toc66641776)

[Figure 6 Expected x-ranges for polarized and un-polarized gluon
distribution measurements in PHENIX using different channels. The blue
bars indicate the PHENIX detector's existing capability while the red
bars indicate the enhanced coverage provided by the proposed silicon
vertex detector upgrade to PHENIX. 15](#__RefHeading___Toc66641777)

[Figure 7 - Gluon shadowing from Eskola as a function of x for different
Q^2^ values: 2.25 GeV^2^ (solid), 5.39 GeV^2^ (dotted), 14.7 GeV^2^
(dashed), 39.9 GeV^2^ (dotted-dashed), 108 GeV^2^ (double-dashed) and
10000 GeV^2^ (dashed). The regions between the vertical dashed lines
show the dominant values of x~2~ probed by muon pair production from
DDbar at SPS, RHIC and LHC energies. 19](#__RefHeading___Toc66641778)

[Figure 8 - Gluon shadowing predictions along with PHENIX coverage. The
red bars indicate the additional range provided by the vertex upgrade,
while the blue bars cover the PHENIX baseline. The three theoretical
predictions are for different Q transferred, blue, green and red lines
are Q = 10, 5 and 2 GeV/c respectively, from Frankfurt and Strikman.
20](#__RefHeading___Toc66641779)

[Figure 9 - Dimuon mass spectrum from E866/NuSea showing the mass region
used in their analysis which excludes masses below 4 GeV. Lower masses
were excluded because of the large backgrounds from open charm in that
region. 21](#__RefHeading___Toc66641780)

[Figure 10 (a) Cross section of the silicon vertex tracker (VTX) along
the beam axis. The inner pixel hybrid layer is located at a radial
distance of 2.5 cm from the beam pipe and extends over \~22cm in beam
direction. The silicon strip outer layers are located at 6, 8 and 10 cm.
All three extend over \~26 cm in beam direction. The Be beam pipe with 2
cm radius is also shown. (b) Cut through the silicon vertex detector in
the xy-plane transverse to the beam axis. The VTX is assembled in two
half shells with small acceptance gaps at top and bottom. The different
layers of each half shell have 5, 7, or 9 rows of silicon detectors,
depending on the radial location of the layer.
24](#__RefHeading___Toc66641781)

[Figure 11 DCA distribution for electrons from Dalitz, charm and beauty
decays simulated through four 1% Si layers on the left and four 2%
layers on the right. 28](#__RefHeading___Toc66641782)

[Figure 12 Signal to Background ratios as a function of minimum electron
p~T~ cut. The signal corresponds to detached electrons from charm decays
using a DCA cut of 200m (circles) or no DCA cut (diamonds). The
background corresponds to electrons from Dalitz decays and photon
conversions which pass the corresponding DCA cuts, assuming four layers
of Silicon with 1 or 2% of a radiation length per layer.
29](#__RefHeading___Toc66641783)

[Figure 13 Correlation between the transverse momentum of the D mesons
and the minimum p~T~ cut applied to the electrons (using a DCA cut of
120m). The points represent the most probable value of the D meson p~T~
while the spread represents the (asymmetric) full width at half maximum.
30](#__RefHeading___Toc66641784)

[Figure 14 The DCA distributions in cm for pions with the inner pixel
having 1%X~0~ thickness. On the left is the DCA for direct pions with pt
\>1 GeV/c and on the right is the DCA for pions from *D*^0^ decay.
31](#__RefHeading___Toc66641785)

[Figure 15 The invariant mass distribution for background pairs from
central Au+Au events. Each pion+kaon pair has a pair p~T~ \> 2 GeV/c.
31](#__RefHeading___Toc66641786)

[Figure 16 The *S/B* for D^0^K with a pt \>2 GeV/c for central Au+Au
events into the west-arm of PHENIX. On the left is the simulation for
1%X~0~ thickness per layer. On the right is simulation for 2%X~0~
thickness per layer. 32](#__RefHeading___Toc66641787)

[Figure 17 The S/B for D^0^+D^0^-\>K with a pt \>2 GeV/c for central
Au+Au events into the west-arm of PHENIX. On the left is the simulation
for 1%X~0~ thickness per layer. On the right is simulation for 2%X~0~
thickness per layer. 33](#__RefHeading___Toc66641788)

[Figure 18 DCA distribution for electrons from Dalitz, charm and beauty
decays simulated through four 1% or 2% Si layers
34](#__RefHeading___Toc66641789)

[Figure 19 Signal to Background ratios as a function of the minimum
electron p~T~ cut. The signal corresponds to detached electrons from
beauty decays using a DCA cut of 200m (circles) or no DCA cut
(diamonds). The background corresponds to electrons from Dalitz decays
and photon conversions which pass the corresponding DCA cuts, assuming
four layers of Silicon with 1 or 2% of a radiation length per layer
35](#__RefHeading___Toc66641790)

[Figure 20 In each panel, the green histogram shows the pseudo-rapidity,
~q~-distribution of the final hard scattered partons, which initiated
the recoil jet; the blue histogram shows the ~q~-distribution of recoil
jets within the barrel VTX acceptance; and the red histogram show the
(^jet^ -~q~)-distribution, where ^jet^ is for the pseudo-rapidity
reconstructed for the recoil jets. Different panels are for the event
samples with direct photon of different transverse momenta, starting
from 4-5 GeV/c in the upper left to 9-10 GeV/c in the lower right panel.
36](#__RefHeading___Toc66641791)

[Figure 21 Correlation between x reconstructed and true *x*-value from
PYTHIA. In the plot on the left, ![](media/image1.wmf) and no jet
information has been used. The plot in the right panel is obtained,
using the reconstructed jet axes in the barrel VTX.
37](#__RefHeading___Toc66641792)

[Figure 22 The relative widths (RMS) of the (x(true) --
x(reconstruct))/x(true) distributions, using the reconstructed jet axes
in the barrel 38](#__RefHeading___Toc66641793)

[Figure 23 - Separation of Upsilon states in the di-electron spectrum
with a vertex detector (yellow) and without (black). The number of s in
this plot represents our expectation for a Au-Au run with a recorded
effective luminosity of \~1 nb^-1^ (see chapter 3.5).
40](#__RefHeading___Toc66641794)

[Figure 24 GEANT model of the VTX detector. It consisted of the
inner-most pixel layer and three outer strip layers.
46](#__RefHeading___Toc66641795)

[Figure 25 (a) Cross section of a pixel detector half ladder designed
for the ALICE experiment. The hybrid pixel detector itself consists of a
readout chip that is connected via solder bump-bonds to a sensor chip.
Every sensor pixel has a corresponding individual signal processing
electronic in the readout chip. They are interconnected with small
solder balls ("bump-bonds") in a flip-chip process. Eight pixel detector
assemblies are wire-bonded to a readout bus structure that runs along
the detector on top of the sensors. The half ladder is mounted onto a
mechanical support with includes embedded cooling lines to remove about
one Watt of power dissipated by the readout chip. (b) Arrangement of two
sensor assemblies with four chips each to form a PHENIX pixel detector
half ladder. A bus connects all readout chips. A pilot module outside of
the acceptance of the sensors interfaces the readout of the half-ladder
to the data acquisition system. 48](#__RefHeading___Toc66641796)

[Figure 26 Photograph of a corner of a pixel detector sensor chip, seen
through a microscope. A guard electrode surrounds the array of pixel
implants. The scribe line defines the outer dimensions of the die.
50](#__RefHeading___Toc66641797)

[Figure 27 Test result of a typical high-quality ALICE1LHCb assembly for
the NA60 experiment: (a) Test pulse injection into readout chip: 8 out
of 8192 pixels are dead, the rest of the pixel array responds. (b)
Source measurement with Sr^90^ to test the bump bonding quality: 3 out
of 8192 bonds are open (or pixels do not respond electrically). (c)
Image of a beta source with shadow of the depletion voltage contact
needle on the silicon sensor. 52](#__RefHeading___Toc66641798)

[Figure 28 Map of working pixels from a source measurement of a thin
ALICE pixel sensor assembly. The sensor assembly consists of five
thinned readout chips of 150 m thickness that are bump-bonded to a 200 m
thick silicon sensor substrate. The fraction of working pixels is
indicated for every chip 52](#__RefHeading___Toc66641799)

[Figure 29 Cross section of the structure of the pixel bus. Two
technical solutions are being investigated. Option (a) contains a
high-density double-layer of signal lines, with a mean line pitch of 70
µm. Option (b) uses a reduced line-density on two signal double-layers
with an average line pitch of 140 µm. 53](#__RefHeading___Toc66641800)

[Figure 30 The vertex spectrometer of the NA60 experiment comprises a
16-plane pixel detector telescope mounted in a 2.5 T dipole magnetic
field in 7 cm to 32 cm distance downstream of the targets. Every plane
is built from four or eight ALICE1LHCb single-chip pixel detector
assemblies, which are mounted on ceramic printed circuit boards
57](#__RefHeading___Toc66641801)

[Figure 31 Average-multiplicity event in collisions of a 158\~AGeV/c
Indium beam with a segmented Indium target, reconstructed with 16 pixel
detector planes during the physics run of NA60 in Fall 2003.
57](#__RefHeading___Toc66641802)

[Figure 32 A schematic view of p+ cathode structure of the pixels.
58](#__RefHeading___Toc66641803)

[Figure 33 A schematic view of the prototype silicon strip sensor.
59](#__RefHeading___Toc66641804)

[Figure 34 Current and capacity characteristics of a prototype sensor.
60](#_Ref54530969)

[Figure 35 Schematic layout of the laser test setup.
61](#__RefHeading___Toc66641806)

[Figure 36 The laser test setup for the strip sensor. 61](#_Ref54530872)

[Figure 37 The prototype detector 62](#_Ref54543695)

[Figure 38 Charge correlations in between x-strips and u-strips found in
tests with a radioactive source and with beams of charged particles.
63](#__RefHeading___Toc66641809)

[Figure 39 Hit residuals from tracks found using the silicon strip
sensors in a test beam experiment. 63](#__RefHeading___Toc66641810)

[Figure 40 CDF Hybrid with dimensions shown. This board contains four
SVX4 chips, local power filtering and traces for power, ground and
data/control signals and is functionally equivalent to the proposed ROC.
69](#__RefHeading___Toc66641811)

[Figure 41 RCC block diagram. This chip, implemented as either a
rad-hard FPGA or a fully digital ASIC, serves primarily as a simple,
state-driven de-multiplexer. Additionally, a FIFO is used to buffer
digitized data allowing simultaneous digitization and readout.
69](#__RefHeading___Toc66641812)

[Figure 42 The top panel shows the sensor and some representative
strips. One possibility for pitch adaptation is alos shown; an on-board
pitch adapter, realized through an extra metallization layer on the
sensor (bottom panel), brings the signal traces to -edge of ladder. This
eliminates dead space along the z coordinate of the ladder and
simplifies the ladder connections. 70](#__RefHeading___Toc66641813)

[Figure 43. ROC top layer w/ major components (SVX4, RCC) and bus
connections shown. There are a relatively small number of additional
passive components required, as shown in the CDF implementation in
Figure 40. Two ROC's read out one sensor, a total of eight are
incorporated in one ladder. The figure is drawn to scale.
70](#__RefHeading___Toc66641814)

[Figure 44 ROC signal trace layers. The figure is drawn to scale with
bus widths given with a 100/100 m trace/spacing assumption.
71](#__RefHeading___Toc66641815)

[Figure 45 FEE Block Diagram. 71](#__RefHeading___Toc66641816)

[Figure 46　 Strip detector production flow chart
72](#__RefHeading___Toc66641817)

[Figure 47 Design concepts studied for the vertex detector support
structures. The center most concept with the constant outer diameter
shell had the highest fundamental frequency.
77](#__RefHeading___Toc66641818)

[Figure 48 　First mode shape that dominated the dynamic structural
stiffness analysis 78](#__RefHeading___Toc66641819)

[Figure 49 Displacement and principle stress from a 1.0g gravity load on
a full mass loaded structure 78](#__RefHeading___Toc66641820)

[Figure 50 3D model of the barrel region on the left and the ladder
structure on the right showing a cooling tube mounted on a C-C thermal
plane and the sensor and electronics on the underside.
79](#__RefHeading___Toc66641821)

[Figure 51 Left panel shows the out of plane distortions and the right
panel shows the bowing for the 0 deg solution.
81](#__RefHeading___Toc66641822)

[Figure 52 The inner region of PHENIX central magnet with the envelopes
of proposed upgrade detectors. The silicon vertex tracker (SVXT), a
micro TPC, and nose cone calorimeters are shown.
84](#__RefHeading___Toc66641823)

[Figure 53 Management chart of the VTX project. The fiscal
responsibilities for the individual tasks are specified in bold letters.
The intitutions participating in each task are given in italic. In
PHENIX the DAQ is a separate subsytem and therefore not connected to the
VTX management. 90](#__RefHeading___Toc66641824)

[Figure 54 The overall schedule for the VTX Project.
106](#__RefHeading___Toc66641825)

[Figure 55 The schedule for the strip layers.
106](#__RefHeading___Toc66641826)

[Figure 56 The schedule for the pixel layers
107](#__RefHeading___Toc66641827)

[Figure 57 The schedule for the auxiliary systems and infrastructure
108](#__RefHeading___Toc66641828)

[Figure 58 Budget profile for the VTX project
109](#__RefHeading___Toc66641829)

**List of Tables**

[Table 1 Occupancy of the VTX layers for central Au+Au collisions at 200
GeV. HIJING event generator and a GEANT model of the VTX detector is
used to calculate the occupancy. 25](#__RefHeading___Toc66641830)

[Table 2 Table of efficiency factors that must be applied to delivered
pp, dAu and AuAu luminosities to calculate expected signal yields. The
single and two track reconstruction efficiencies are for electrons in
the central arm. 41](#__RefHeading___Toc66641831)

[Table 3 Table of effective luminosities from a 19 week production run,
after reality factors are taken into account. The delivered luminosities
use the average of the most pessimistic and most optimistic C-AD
estimates of how the luminosity will evolve by 2008-2009. The signal
yield for a given process is found by multiplying the cross section for
the process by the effective luminosity and by the detector acceptance.
For d-Au and Au-Au collisions and the effective Ldt columns, the
nucleon-nucleon luminosities are shown in the parenthesis).
41](#_Ref54638032)

[Table 4 Event rate calculated for selected physics processes. The
effective integrated luminosity used in the calculation is shown in
Table 3. For the meaning of "no VTX" column, see the text. In both of
Au+Au and p+p, the collision energy $\sqrt{s_{\text{NN}}}$ is 200 GeV
per nucleon pair. The yields include the anti-particle channels. The DCA
cut value for the single electron measurement is DCA\>200 . For the
lowest pT bin, the number with DCA\>400 is shown in parenthesis.
44](#__RefHeading___Toc66641833)

[Table 5 Summary of physics measurement gained by the VTX detector. The
column "without VTX" shows the present capability of PHENIX, while the
measurement range with the VTX detector is shown in the column "with
VTX". If the process is not measurable, it is marked as "No".
45](#_Ref54757390)

[Table 6 Summary of main parameters of the 4 VTX layers.
47](#__RefHeading___Toc66641835)

[Table 7 Si strip detector test schedule
73](#__RefHeading___Toc66641836)

[Table 8 Professional Background of the lead managers in the VTX
project. 91](#__RefHeading___Toc66641837)

[Table 9 Collaboration members working on the inner-layer/pixel
sub-task. 93](#__RefHeading___Toc66641838)

[Table 10 Collaboration members working on the outer/strip sub-task.
93](#__RefHeading___Toc66641839)

[Table 11 Collaboration members working on the auxiliary
systems/integration sub-task. 94](#__RefHeading___Toc66641840)

[Table 12 Collaboration members working on the software sub-task.
94](#__RefHeading___Toc66641841)

[Table 13 Collaboration members working on the DAQ sub-task.
94](#__RefHeading___Toc66641842)

[Table 14 Map of construction tasks and WBS numbers onto the proposed
fiscal responsibilities. 103](#__RefHeading___Toc66641843)

[Table 15 Overview of the total estimated cost for the VTX project
103](#__RefHeading___Toc66641844)

[Table 16 Cost breakdown for tasks to be funded through the DOE. Tasks
which do not show a cost correspond to deliverables for which the RIKEN
Institute will take fiscal responsibility.
104](#__RefHeading___Toc66641845)

# 1. Executive Summary

We propose the construction of a Silicon Vertex Tracker (VTX) for the
PHENIX experiment at RHIC. The VTX will substantially enhance the
physics capabilities of the PHENIX central arm spectrometers. Our prime
motivation is to provide precision measurements of heavy-quark
production (charm and beauty) in *A+A*, *p(d)+A*, and polarized *p+p*
collisions. These are key measurements for the future RHIC program, both
for the heavy ion program as it moves from the discovery phase towards
detailed investigation of the properties of the dense nuclear medium
created in heavy ion collisions, and for the exploration of the nucleon
spin-structure functions. In addition, the VTX will also considerably
improve other measurements with PHENIX. The main physics topics
addressed by the VTX are:

-   Hot and dense strongly interacting matter

    -   Potential enhancement of charm production

    -   Open beauty production

    -   Flavor dependence of jet quenching and QCD energy loss

    -   Accurate charm reference for quarkonium

    -   Thermal dilepton radiation

    -   High *p*~T~ phenomena with light flavors above 10-15 GeV/c in
        *p*~T~

    -   Upsilon spectroscopy in the ee decay channel

-   Gluon spin structure of the nucleon

    -   G/G with charm

    -   G/G with beauty

    -   x dependence of G/G with -jet correlations

-   Nucleon structure in nuclei

    -   Gluon shadowing over broad x-range

With the present PHENIX detector, heavy-quark production has been
measured indirectly through the observation of single electrons. These
measurements are inherently limited in accuracy by systematic
uncertainties resulting from the large electron background from Dalitz
decays and photon conversions. In particular, the statistical nature of
the analysis does not allow for a model-independent separation of the
charm and beauty contributions.

The VTX detector will provide vertex tracking with a resolution of \<50
m over a large coverage both in rapidity (\| \| \< 1.2) and in azimuthal
angle ( \~ 2). With this device, significantly enhanced and
qualitatively new data can be obtained. A more robust and accurate
measurement of heavy-quark production over a wide kinematics range will
be possible.

The main benefits are in three areas. Firstly, by selecting electrons
with a distance of closest approach (DCA) to the primary vertex larger
than \~100 m, the background will be suppressed by several orders of
magnitude and thereby a clean and robust measurement of heavy flavor
production in the single electron channel will become available.
Secondly, because the lifetime of mesons with beauty is significantly
larger than that of mesons with charm, the VTX information will allow us
to disentangle charm from beauty production over a broad *p*~T~ range.
Thirdly, a DCA cut on hadrons will reduce the combinatorial background
of *K* to an extent that a direct measurement of *D* mesons through this
decay channel will become possible. In addition, the VTX detector will
substantially extend our *p*~T~ coverage in high *p*~T~ charged
particles, and it also will enable us to measure +jet correlations.

The proposed VTX detector has four tracking layers. To avoid cost
intensive and time consuming R&D, we have investigated to what extent
existing technology can meet our needs. For the inner most layer we
propose to use a silicon pixel device with 50425 m channels that was
developed for the ALICE experiment at the CERN LHC. Our preferred
technology choice for the outer layers is a silicon strip detector
developed by the Instrumentation Division at BNL. With stereoscopic
strips of 80 m 3 cm, these devices achieve an effective pixel size of 80
1000 m. We plan to use the SVX4 readout chip developed at FNAL to
readout the strip detectors.

With the help of institutional contributions PHENIX was able to maintain
a small but well focused effort over the past two years to gain
experience with these technologies and to launch the necessary R&D to
adapt them to the PHENIX requirements. We are confident that the
remaining issues can be solved within the next year and that the
detector construction could be started by beginning of FY05.

A collaboration of 66 members from 13 institutions has formed to carry
out the project. The collaboration brings in expertise in all phase of
the construction of a silicon vertex detector, design and commissioning
of modern readout electronics, mechanical and integration issues,
detailed knowledge of all aspects of the PHENIX experiment as well as
expertise in data analysis and a broad interest in different physics
aspects addressed by the VTX.

We anticipate that the project will be funded by two agencies, the DOE
Office of Nuclear Physics and the RIKEN Institute of Japan. For a
successful completion of the project we propose clear responsibilities
and scope of deliverables for both agencies. A preliminary management
plan of the VTX detector project, which also discusses the role and
expected responsibilities of the participating institutions, is included
in this document.

We propose to construct the VTX detector over a period of three years,
US FY05, FY06 and FY07. Parts of the detector will be ready and
installed in time for the expected RHIC run in (RUN7). The project will
be completed before RUN8. To carry out this project we seek funding of a
total of \$5.6M through DOE. These funds would be supplemented with
deliverables equivalent to about \$3M US dollar provided by the RIKEN
Institute during calendar years 2004 to 2006.

The proposal has the following structure. The physics motivation for the
upgrade and the proposed measurements are documented in section 2. The
feasibility of these measurements and the required detector performance
are discussed in section 3. Section 4 gives a detailed description of
the vertex tracker and the technical aspects of the proposed project. A
draft of our management plan, section 6, specifies deliverables and
institutional responsibilities. Section 7 lays out the budget request
and the proposed schedule. Finally, in appendix A we present our future
plan to also upgrade the PHENIX muon arms with vertex tracking by
augmenting the silicon barrel detector proposed here by end-cap
detectors.

# 2. Physics Overview

Heavy-flavor production provides a wide-ranging palette of key
information in three broad areas of physics addressed by the
relativistic heavy ion collider RHIC at Brookhaven National Laboratory.
Current experiments at RHIC are inadequately equipped to fully exploit
the opportunities heavy-flavor production provides. Many of the
necessary measurements are either not possible or can be performed only
with very limited accuracy. Precise vertex tracking is imperative for a
robust measurement of heavy-flavor production. The proposed VTX detector
adds tracking capabilities to the central arms of the PHENIX experiment.
With this detector charged particles detected in the central arms can be
identified as decay products from charm- or beauty-carrying particles by
the displacement of their trajectories to the collision vertex. A broad
*p~T~* range for charm and beauty measurements is achieved by using
different decay channels to reach different parts of phase space.

The addition of the VTX to PHENIX will significantly extend the physics
program of PHENIX. In heavy ion collisions open charm and beauty
production will provide essential new data on the high-density matter
created early during the reaction. Specifically, these measurements will
determine:

-   if heavy-quarks are produced only in the initial parton-parton
    collisions or also during the later phases of the collision.

-   the flavor dependence of the energy-loss, which has already been
    observed for light partons.

-   a firm baseline to quantify the suppression or possible enhancement
    of J/

-   quantitatively the rate of thermal dilepton emission.

-   quark confinement forces at larger binding energies via the yield of
    upsilon states.

Measurements of open beauty in polarized *p+p* reactions add new
channels in which the gluon spin structure function of protons can be
measured. Robust charm measurement and jet reconstruction over large
acceptance significantly extend the *x*-range of the currently possible
measurements. In *p+A* reactions shadowing of the gluon structure
function in nuclei can be addressed both with open charm and beauty
measurements.

## 2.1 Probes of Early, Highest Energy-Density Stage of Heavy-ion Reactions

As RHIC moves to the second half of this decade the research focus will
shift from the discovery phase to a detailed exploration of quark
matter. Charm and beauty production, measured as yield and spectra of
heavy flavor mesons, provide information about the earliest stages of
heavy ion collision. Several key measurements discussed in these
sub-sections can be made with the addition of the proposed VTX detector
to PHENIX. Of particular importance is the broad reach in transverse
momentum, which extends PHENIX's existing capability to measure
low-*p~T~* open charm.

PHENIX has extracted the cross-section for open charm in the momentum
range *p~T\ ~*\< 2 GeV/c via inclusive electron spectra[^1]. This method
relies on the fact that a fraction of the electrons originates from
decays of heavy-flavor mesons (charm or beauty) and on the ability to
subtract the large background from light-meson decays. This procedure
suffers from uncertainties due to the limited knowledge of the
background sources that are subtracted. The addition of a silicon vertex
detector to PHENIX will allow a much more convincing and accurate
determination of the heavy-quark component in these spectra. Requiring
the leptons to be displaced from the collision will substantially reduce
the background and thus extend the range of the charm measurement to
smaller *p~T~*. At moderate and high *p~T~* decays of beauty-flavor
mesons also contribute to the single-electron spectrum. The present
PHENIX detector cannot distinguish the charm from the beauty
contribution and thus our ability to measure charm is limited to
*p^e^~T~* \< 2.5 GeV/c, i.e. the range where charm is the dominant
source of single electrons after background subtraction. The proposed
upgrade adds the capability to detect charm and beauty production
separately with high accuracy, which will enable us to measure not only
the yield of open beauty production but also to extend the charm
measurement to higher *p~T~*. Complementary to the measurement of
inclusive electrons with displaced vertex, at high p~T~ we can also
measure exclusive decays such as $D \rightarrow K\pi$.

With the extended capability of heavy quark measurement with the VTX
detector, we can address the following critical questions.

### Potential enhancement of open charm production

It has been predicted that open charm could be enhancement in
high-energy nucleus-nucleus collisions relative to the expectation from
elementary collisions[^2]^,^[^3]^,^[^4]. Heavy quarks are produced in
different stages of a heavy ion reaction. In the early stage charm and
beauty are formed in collisions of the incoming partons. The yield of
this component is proportional to the product of parton density
distribution in the incoming nuclei (binary scaling). If the gluon
density is high enough a considerable amount of charm can be produced
via fusion of energetic gluons in the pre-equilibrium stage before they
are thermalized. Finally, if the initial temperature is above 500 MeV,
thermal production of charm can be significant. The last two mechanisms
(pre-equilibrium and thermal production) can enhance charm production
relative to binary scaling of the initial parton-parton collisions.
These are the same mechanisms originally proposed for strangeness
enhancement, but in the case of charm may reveal more about the
critical, early partonic-matter stage of the reaction since the rate of
heavy-quark production is expected to be negligible later in the
reaction when the energy density has decreased. In comparison,
strangeness production is expected to continue even in the later
hadronic stages of the reaction.

![](media/image2.jpeg){width="2.7222222222222223in"
height="3.0375in"}![](media/image3.jpeg){width="2.428472222222222in"
height="2.9763888888888888in"}

[]{#__RefHeading___Toc66641772 .anchor}Figure 1 Charm enhancement
expected at RHIC energy from ref. Error: Reference source not found. In
both panels, contribution from the initial gluon fusion (solid),
pre-thermal production (dot-dashed), and thermal production (dashed,
lowest) are shown. The left panel is the calculation with energy density
of 3.2 GeV/fm^3^, while the right panel shows the case with energy
density 4 times higher.

At RHIC energies the anticipated enhancement is small effectError:
Reference source not found^,Error:\ Reference\ source\ not\ found^. The
contributions to charm production from various stages of an Au+Au
collision are shown in Figure 1 (taken from reference Error: Reference
source not found). From the left panel of the figure it is evident that
for an initial energy density of 3.2 GeV/fm^3^ the pre-thermal or
pre-equilibrium production contributes about 10% of total charm
production, while the thermal contribution is negligible. However, the
yield is very sensitive to the initial density, and with 4 times the
energy density the pre-equilibrium contribution can be as large as the
initial fusion. This is illustrated in the right panel of the figure.
Present single electron measurements of PHENIX indicate that within
\~40% systematic uncertainty charm production approximately scales with
the number of binary collisions. Thus, charm enhancement, if it exists,
cannot be a large effect. A measurement of the charm yield with
substantially higher accuracy and precision is therefore required to
establish a potential charm enhancement.

The VTX detector will improve the accuracy of charm measurement through
single electrons by significantly reducing the background from Dalitz
and photon conversions. This will extend the single electron measurement
to the *p*~T~ region below 0.5 GeV/c, which is essential for an accurate
determination of the total charm yield since more than half of the
single electron yield from charm decays is in this *p*~T~ region.

### Open Beauty Production

Beauty quarks are predominantly produced by the initial parton-parton
collision. Because of the large mass almost no additional production is
expected from the pre-equilibrium stage or thermalized phase. As a
consequence, the measurement of open beauty is ideally suited to probe
the parton density in the coming nucleus and thus the initial parton
luminosity.

The open beauty yield can be measured via inclusive electron production,
or more directly through its decay *B J/ +X* (B.R. 1.14%). The VTX
detector is essential for the detection of both channels. In the single
electron measurement, we cannot distinguish single electrons from open
charm and open beauty with the present PHENIX detector. Below *p*~T~ \~
2.5 GeV/c the open charm contribution to the non-photonic electron
spectrum, which is the inclusive electron spectrum after subtraction of
the light meson decay background, is much larger than that of beauty.
Thus, it is not possible to determine the open beauty component in this
low *p*~T~ range. This is the *p*~T~ range that contains about 90% of
the electrons from beauty decays. Even in the high *p*~T~ region
(*p*~T~\>3 GeV/c), where beauty is expected to be the leading source of
non-photonic electrons, there is a large uncertainty due to the unknown
charm contribution. Since beauty has a larger *c* (*B*^0^: 462 m,
*B^+^*: 502 m) than charm (*D*^0^: 123 m, *D^+^*: 317 m), we can
accurately split the beauty component of single electron from the charm
component using a precise displaced vertex measurement from the VTX.

The VTX also enables us to measure the *BJ/X* decay by tagging *J*/\'s
with a vertex detached from the collision point. Although this mode has
a small cross section, it gives a clean signal of *B* in wide momentum
range, down to *p*~T~ = 0.

### Ratio of charm and beauty production and its centrality dependence

One of the interesting opportunities opened by a beauty measurement
using the VTX is the extraction of the (*ce*)/(*be*) ratio as function
of the collision centrality. In this ratio, most of the systematic
uncertainties including acceptance, reconstruction efficiency,
luminosity, and number of collisions per event cancel. In addition,
since little or no enhancement of beauty relative to binary scaling is
expected at RHIC energy, the denominator (*b* *e*) may serve as a
precise monitor of the initial parton luminosity, a role similar to that
of Drell-Yan production of muon pairs for J/ suppression measurement by
NA50. This ratio could provide a very sensitive method to observe a
small charm enhancement like it was discussed in the previous section.
As discussed in section 3.5, we could obtain an accuracy of the
centrality dependence of this ratio close to \~1 % in statistical
precision.

### Energy-loss of heavy-quarks

Colored high-pt partons are predicted to lose energy as they propagate
through the dense nuclear medium[^5]. The dominant mechanism is likely
medium-induced gluon radiation[^6],[^7] with a smaller contribution from
elastic collisions with lower-energy partons. Gluon radiation and
energy-loss are exquisitely sensitive to interference effects, since the
gluon formation time is comparable to the time between successive
collisions. Hence before we can quantitatively use the measured
energy-loss as a probe of the dense medium, we need to be confident that
the interference effects in the model calculations are well tested by
data. One powerful strategy is to change the amount of
gluon-interference by using heavy-quarks instead of light quarks.

![](media/image4.jpeg){width="3.3541666666666665in"
height="2.236111111111111in"}

[]{#__RefHeading___Toc66641773 .anchor}Figure 2 Ratio of Jet Quenching
factor QH/QL of heavy quark (QH) and light quark (QL) in high density
QCD medium as function of pT of the quark, from ref. Error: Reference
source not found. The solid line is with no energy cut-off for gluon and
the dashed line is with cut off of 0.5 GeV.

Heavy-quarks are predicted[^8] to lose less energy in the plasma because
of the "dead-cone effect". Qualitatively the large quark mass eliminates
the favored collinear gluon Bremsstrahlung. It also shortens the gluon
formation time and leads to a distinctly different destructive
interference around the heavy-quark's trajectory. Figure 2 shows the
ratio of jet quenching factor Q~H~/Q~L~ for heavy quarks (Q~H~) and
light quarks (Q~L~) as function of the *p*~T~ of the quark calculated in
reference Error: Reference source not found. The smaller energy loss due
to the "dead cone" effect leads to a factor of 2 less suppression of
high *p*~T~ charm quarks compared to light quarks.

Recent studies suggest that the magnitude of the
dead-cone[^9]^,^[^10]^,^[^11] may be smaller than anticipated in
reference Error: Reference source not found, which would lead to an
energy-loss for heavy quarks closer to that for light quarks. Djordjevic
and GyulassyError: Reference source not
found^,Error:\ Reference\ source\ not\ found^ have proposed that the
energy-loss for heavy-quarks is further reduced due to a plasmon
frequency cut-off effect in a thermalized medium. As a result precise
measurement of heavy-quark energy loss through open charm may enable a
measurement of partonic effective thermal masses in the medium.

As the opposite extreme, Batsouli *et al*[^12] have suggested that the
first electron measurements at RHIC can be reproduced by assuming that
charm particles flow hydrodynamically, i.e. the charm particles interact
with the medium with a large cross-section. To distinguish between these
effects and to explore this physics will require measuring the *p*~T~
spectra for open charm at high transverse momentum, out to several
GeV/c. This point is illustrated in Figure 3. The figure, taken from
reference Error: Reference source not found, illustrates that the *p*~T~
distribution of *D* mesons and single electrons from charm have little
difference in the two extreme scenario of no medium effect (shown in
dashed curves) and hydrodynamic model (shown in solid curves) within the
*p*~T~ range accessible by the current PHENIX setup. Obviously, a
measurement at much higher *p*~T~ range is required to distinguish the
models. Such a measurement is not feasible without the VTX upgrade.

![](media/image5.jpeg){width="4.054166666666666in"
height="3.438888888888889in"}

[]{#__RefHeading___Toc66641774 .anchor}Figure 3 Single electron data of
PHENIX compared with two extreme models of charm *p*~T~ distribution.
From ref. Error: Reference source not found.

Using the displaced vertices of kaons and pions we will be able to
measure the high-*p*~T~ spectra of charm directly via the hadronic decay
channels, e.g. *DK*+ In addition, it will also be possible to separate
single electrons from beauty and charm decays. This extends the momentum
range of charm measurement in the inclusive electron channel from
*p*~T~^e^ \< 2.5 GeV/c to *p*~T~^e^ \~ 6 GeV/c into the range where the
effect of finite energy loss of charm quark is expected.

### Open charm reference to J/ suppression and enhancement

In the J/ studies done at CERN by NA38/50[^13] the J/ yields were
usually determined relative to the Drell-Yan di-muon yields with the
argument that the latter should have little final-state nuclear
dependence. But it is not clear how reliable this comparison really is
since the Drell-Yan process involves quarks ($q\overline{q}$
annihilation) while J/ production involves gluons (gluon fusion). It is
likely that the nuclear effects on the initial parton distributions for
quarks and gluons as well as their energy loss in the initial state
before the hard interaction are different. Additionally, the yield of
Drell-Yan dimuon pairs is quite small and thus limits the statistical
accuracy of the measurement. It seems much more natural to compare J/
production to open-charm production, where the initial-state effects are
probably the same. Therefore a robust measurement of open-charm is quite
important for the physics of the J/. At CERN this is now provided by the
NA60 experiment. It has also been suggested by some theoretical
groups[^14] that the effective gluon distributions are process
dependent, and different for e.g. open- and closed-charm production.
These models suggest that comparisons of open and closed charm are
important to establish the extent of higher-twist contributions to
closed charm production.

![](media/image6.jpeg){width="3.734027777777778in"
height="3.0368055555555555in"}

[]{#__RefHeading___Toc66641775 .anchor}Figure 4 The ratio of J/ yield
and open charm yield predicted in ref. [^15]

Recently, a new mechanism for charmonium production in high-energy
nucleus-nucleus collisions has been proposedError: Reference source not
found^,^[^16]^,^[^17]. The basic idea is that charmonium can be formed
by re-combination of *c* and $\overline{c}$quarks when the bulk of the
hadrons are formed. Since about 10 to 20 $c\overline{c}$ pairs are
produced in a single event in central Au+Au collisions at RHIC, this
contribution can be very significant. It has been predicted that the
charmonium yield increases with the square of the open charm yield.
Figure 4 shows a prediction of reference Error: Reference source not
found, one of the recombination models. In this model, the ratio of J/
yield over open charm yield has a minimum at $\sqrt{s}$\~ 40 GeV due to
interplay between J/ suppression in QGP and J/ formation via
recombination mechanism. An accurate measurement of charmonium to open
charm ratio over a broad range of impact parameters and collision
energies is essential to test these models.

### Open beauty and J/suppression

Another important area, especially for J/ measurements, is the
production of beauty quarks. The decay of *B* mesons will produce J/'s
(BR \~ 1.14%) that tend to have somewhat higher *p*~T~ than prompt J/
production. In a scenario where color-screening in a QGP destroys most
of the primary J/'s, it is conceivable that a large fraction of the
observed J/'s comes from *B* decays. An estimate by Lourenco[^18]
several years ago indicated that for central collisions the fraction of
J/'s from *B* decays might be as large as 20% overall, with even larger
fractions at high *p*~T~. Clearly one would like to measure the *B*
cross sections at RHIC energies so that a more reliable estimate of
their contribution to the J/ production can be made, an issue which
would be particularly important should a large suppression of J/'s be
seen in central Au-Au collisions at RHIC. How strong the suppression
actually is will be difficult to quantify without establishing how many
of the remaining J/'s do come from *B* decays.

### Thermal di-lepton and open charm

The hot and dense system that is created in the heavy ion collision
should emit electro-magnetic radiation during its time evolution, either
in the form of real photons, or in the form of virtual photons, which
materialize as lepton pairs. This thermal electro-magnetic radiation
directly probes the dense system. The production rate of the thermal
di-leptons is a steep function of temperature, and thus an accurate
measurement may enable us to determine the initial temperature of the
system.

![](media/image7.png){width="3.5131944444444443in" height="2.975in"}

[]{#__RefHeading___Toc66641776 .anchor}Figure 5 The di-electron
effective mass distribution in PHENIX central arm acceptance in central
Au+Au collision at $\sqrt{s_{\text{NN}}}$= 200 GeV predicted by
RappError: Reference source not found. In the intermediate mass region
(1 \< Mee \< 2.5 GeV), the dominant sources of electron pairs are open
charm and thermal radiation from the QGP and hot hadronic gas.

There are several processes that contribute to the di-lepton continuum.
Qualitatively, the Drell-Yan process dominates the high-mass region,
while thermal pairs from the hadron gas dominate the low-mass region. At
RHIC energies, thermal radiation from the quark-gluon plasma is
predicted to be the major source of di-leptons in the intermediate mass
region of 1\<M~ee~\<3 GeV. In this mass range thermal radiation competes
with a large background from semi-leptonic decays of correlated
$D\overline{D}$pairs. Figure 5[^19] compares predictions for the thermal
di-electron continuum above the resonance to di-leptons from open charm.
The di-electron yield from open charm is comparable to the thermal
di-lepton signal at M~ee~=1 GeV, and is two to three times as large in
the mass range of 1.5 to 2.5 GeV. It is clear that one cannot extract
the thermal dilepton yield without knowledge of open charm contribution.
Knowledge of single electron production from open charm is insufficient
to subtract this contributions, since the mass of the di-lepton also
depends on the correlation between the $D$ and $\overline{D}$ mesons.
Thus it is imperative to directly measure the di-lepton spectrum from
correlated charm pairs in order to observe and to accurately determine
the thermal dileptons from the quark-gluon plasma. This measurement will
only be possible with the VTX upgrade.

### High *p*~T~ phenomena with light flavor in 10 -- 15 GeV/c in *p*~T~

The suppression of the high *p*~T~ particle production is probably the
most direct evidence of formation of very dense matter in high-energy
nucleus-nucleus collisions at RHIC so far. The creation of dense matter
is now firmly established from the high *p*~T~ data in Au+Au collision
and the comparison data in d+Au collisions. The natural next step is to
extend the data, now in *p*~T~ range of up to 10 GeV/c, to reach much
higher *p*~T~ to study the nature of the high *p*~T~ suppression.

In the present PHENIX detector, the *p*~T~ range of the charged particle
measurement is limited to 10 GeV/c in *p*~T~ due to a large background
from photon conversion and decay in flight of light mesons. The present
central arm spectrometer suffers from these backgrounds since it
measures particle tracks only outside of the magnetic field. Thus, it
cannot distinguish a real high *p*~T~ track that originates from the
event vertex from a background track that is produced far from the
vertex either by photon conversion or by decay-in-flight. The VTX
detector will eliminate these backgrounds by providing additional
tracking near the event vertex. In addition, the VTX measurement will
improve the *p*~T~ resolution by about a factor of three (see 3.4) by
measuring the initial emission angle of the track in a slightly
increased magnetic field. Combined, the *p*~T~ range of the charged
particle measurement in PHENIX will be extended to beyond 15 GeV/c or
more, and will be limited only by the statistics.

### Measurement of Upsilon states

Given sufficient RHIC luminosity, we will be able to measure the -states
($b\overline{b}$bound states), and to compare closed and open-beauty
production. It is particularly interesting to measure the relative yield
of the three states, as we can study the suppression of heavy quarkonia
as function of the binding energy in a region of large binding energy
that is not accessible by charmonium production. In addition, unlike
charmonium, the contribution to production due to quark recombination
must be negligible since the number of $b\overline{b}$ pairs produced in
an event is very small. Thus in the production we can directly access
the de-confinement effect in dense matter. As mentioned previously with
the VTX detector, the momentum resolution will be improved by about
factor three, which reduces the mass resolution to \~ 60 MeV so that a
clean separation of the 1S, 2S and 3S states becomes possible. However,
this measurement will only be possible if luminosities significantly
above the RHIC design value of 2×10^26^ cm^-2^ are reached.

## 2.2 Determination of spin structure of nucleon.

### Exploring the spin structure of the nucleon: The past

Most of what we know about the origin of the nucleon spin comes from
Deep Inelastic Scattering (DIS) experiments performed over the last
three and half decades. These experiments used polarized electron or
muon beams in the momentum range 20-200 GeV/c to impinge on stationary
polarized gaseous or solid-state targets. The partonic interaction that
occurs in such experiments is between the virtual photons (coming from
the polarized lepton beams) and the quarks inside the nucleons of the
stationary targets. Naturally, DIS is an excellent probe of the quark
polarization in the nucleons. In the late 1980s, measurements were made
for the first time at higher energies and a significant deficit in the
quark contribution to the nucleon spin was discovered. Often called in
the literature "Spin Crisis", the quest to understand this deficiency
has driven the experimental and theoretical work in the field of nucleon
spin since then. Where is the rest of the nucleon spin? The obvious
place to look is the gluons and to measure their contribution. The
virtual photons in the DIS only interact weakly with the gluons, as
such, one can access the gluon spin dynamics in DIS only through scaling
violations of spin structure functions which requires their measurement
over a large range of x and Q^2^. As of today, such an experimental
facility is unavailable and so one has to consider other techniques and
tools to access the gluon spin.

### Gluon polarization measurement at RHIC:

The new tool that we have been waiting for is the Relativistic Heavy Ion
Collider (RHIC). It enables collisions between polarized proton beams at
high energy (up to 250 GeV/c). The expected luminosities at these top
beam energies are 2x10^32^ cm^-2^ sec^-1^. As of now, 100 GeV/c
polarized protons have been collided with few x 10^30^ cm^-2^ sec^-1^
luminosity. Since protons are abundant sources of gluons, polarized
proton-proton collisions allows a direct exploration of the gluon spin
dynamics at the partonic level. The differences in the hadronic final
states originating from gluon-gluon and quark-gluon interactions in the
polarized proton collisions measured by the detectors when the proton
spins in the two colliding beams are aligned vs. anti-aligned gives us
access to the gluon spin contribution to the proton. For a partonic
interaction of the kind (a+b c+d) occurring in polarized pp collisions,
assuming factorization one can write:

$A_{\text{LL}} = \frac{\Delta a}{a}\frac{\Delta b}{b}a_{\text{LL}}(a + b \rightarrow c + d)$
(1)

Here *a/a* and *b/b* are the ratios of polarized to unpolarized
distributions for parton distributions of *a* and *b* respectively, and
*a~LL~* is partonic analyzing power calculable in pQCD. *A~LL~* is the
double spin asymmetry measured in the experiment as a result of the
polarized proton proton scattering for the final state in which *c* and
*d* are created and measured in the detector. In this particular
example, either *a* or *b* or both could be gluon distributions in the
colliding protons.

In the PHENIX experiment we will measure gluon spin polarization G/G
using many different processes. A partial list includes gg, gq in the
partonic initial state resulting in different final states:

1)  inclusive neutral and charged pions

> $$a_{\text{LL}}(\text{gg},\text{gq} \rightarrow \pi^{0, \pm},X)$$

2)  inclusive photon production (direct or prompt photon production)

> $$a_{\text{LL}}(\text{gg},\text{gq} \rightarrow \gamma + X)$$

3)  charm & anti-charm and beauty-anti-beauty pair production

> $$a_{\text{LL}}(\text{gg},\text{gq} \rightarrow \overline{c}c,\overline{b}b + X)$$

4)  direct photon production along with jet

> $$a_{\text{LL}}(\text{gg},\text{gq} \rightarrow \gamma + \text{jet} + X)$$

For different final states, experimentally we measure the following
double spin asymmetry (a counting rate asymmetry):

$A_{\text{LL}} = \frac{1}{P_{B}P_{Y}} \ast \frac{N_{\text{++}} - R \ast N_{+ -}}{N_{\text{++}} + R \ast N_{+ -}}$
(2)

Where P~B/Y~ are the blue and yellow beam polarizations, *N*~++/+-~ the
counting rates measured with the ++(parallel) and +-(anti-parallel)
orientations of the proton beam spin vectors and R is the ratio of
luminosities for ++ and +- spin orientation collisions. (Ideally, R=1).

### The role of Silicon Vertex Detector:

The different channels with which PHENIX can make measurements of the
gluon polarization cover different kinematic regions in x and Q^2^.
Figure 6 shows the x coverage possible with RHIC p-p running at 200 GeV
center of mass, \~70% beam polarization and \~300 pb^-1^ luminosity
(delivered) with the PHENIX detector for the above mentioned physical
processes under two different scenarios. Here x is the gluon momentum
fraction of the proton momentum, and "coverage" implies we measure the
ratio G/G with \~20% relative uncertainty of its expected value at that
x. The baseline PHENIX detector is capable of covering a range: 0.02 \<
x \< 0.3 (shown in blue). We note that although the coverage extends
over one decade in x, between the different channels there is little
overlap. The coverage extended by the VTX silicon is shown in the same
figure (in red).

The proposed silicon vertex detector will be crucial in the
determination of gluon distribution in two significant ways:

1)  Different measurements will cover the same kinematic regions: this
    would enable the much-needed cross-checks within PHENIX for
    accessing the polarized gluon distribution. The vertex detector
    extends the reach in *x* for many of the measurements and hence adds
    a significant amount of overlap in *x*-range coverage.

2)  By being able to observe displaced vertices at low-pt for
    semi-leptonic decays of charm and beauty, the VTX detector enables a
    larger x-range over which we will make gluon polarization
    measurements. It is estimated that the x reach of the silicon-vertex
    upgraded PHENIX will be 0.01 \< x \< 0.3.

![](media/image8.png){width="4.506944444444445in"
height="3.6618055555555555in"}

[]{#__RefHeading___Toc66641777 .anchor}Figure 6 Expected x-ranges for
polarized and un-polarized gluon distribution measurements in PHENIX
using different channels. The blue bars indicate the PHENIX detector's
existing capability while the red bars indicate the enhanced coverage
provided by the proposed silicon vertex detector upgrade to PHENIX.

Since the two measurements of open charm and beauty and of gamma+jet
crucially depend on the silicon vertex detector more details are
provided on these two channels below.

### The heavy quark physics (open charm and beauty production)

By requiring an additional cut on displaced vertex information coming
from the vertex detector, we gain significantly in the robustness of the
heavy-quark results by improving the purity of the event sample.

We plan to observe charm production through its semi-leptonic decay to
*e*^±^. We will need a good vertex resolution to identify the displaced
vertices in such events. The main backgrounds expected for this physics
include Dalitz decays and photon conversions. This has been studied
(Section 3.2) using a GEANT detector simulation. We estimate that the
SVTX could achieve \~50m DCA resoluiton. Using a DCA cut value \~200 m
for tracks with *p*~T~ \> 1 GeV/c, we should be able to achieve a
significant background reduction. As a result of the DCA cut the purity
of the event sample increases from \~50% to \~90% (see Figure 12 in
section 3.2).

Another possible channel to access gluon distributions is open beauty
production. Beauty production measured at the Tevatron at 1.8 TeV, and
the next-to-leading order pQCD calculation missed the data by factor of
2 or greater. The discrepancy between the experimental data and the
theory has sparked much debate and excitement recently. New data on
beauty production would be crucial, especially at RHIC, since they would
be obtained at different values of s (200 and 500 GeV).

Measurements of beauty production can be performed in the present PHENIX
detector using electron-muon coincidence using the central and forward
muon arms. With the limited acceptance for the detector subsystems, this
results in a narrow kinematics coverage and small detection cross
section. With the VTX detector, we have two additional channels to
measure beauty production at RHIC: the single electron in the central
arm and *B*J/+X. The single electron channel provides us much higher
statistics compared with the -*e* channel.

The main background in the *b* physics measurements is expected from the
charm semi-leptonic decay, Dalitz decays, and photon conversions.
Information provided by the VTX detector will enable a cut on the DCA to
produce a highly pure sample of events involving beauty quarks with less
than \~10% impurity from charm quark events in the low *p*~T~ range (\<
3 GeV) and even purer *b*-sample at higher *p*~T~. Without the VTX this
impurity is expected to be more than 75% (see Figure 19, section 3.2).
The VTX and the DCA analysis of data it will thus produce a reliable
data set highly devoid of charm events and other impurities for the
comparison with theory for beauty production cross section.

The displaced vertex resolution possible with the VTX detector enables
additionally one more measurement: *B*J/+X. *B* mesons could be
identified with J/ decays detected as displaced electron-pair vertices.
This process identifies open beauty production with no charm
contribution and will be a clean probe of the polarized and the
un-polarized gluon distributions.

Finally, a recent theoretical study (I. Bojak, Ph.D. Thesis, April 2000,
Univ. Dartmund) of the expected values of the open charm and open beauty
asymmetries at high energy concluded that they would be of the order of
a few times 10^-3^ at RHIC energies. The open beauty asymmetries are
expected to be slightly larger (private discussions with W. Vogelsang).
False asymmetries related to bunch-to-bunch variation of luminosity in a
collider are potentially a show-stopper for any spin measurement if they
are comparable in magnitude to the asymmetry one is interested in.
However, from the ongoing RUN 3 analysis we already know at RHIC these
false asymmetries can be controlled to be smaller than a few times
10^-4^. Although this situation could potentially get worse with the
RHIC luminosity increase (due to difficulties associated with handling
higher beam currents), additional tools are being discussed at RHIC that
are expected to reduce uncertainties due to such effects by a factor of
\~10 using techniques such as simultaneous spin flips in both RHIC beams
using a spin flipper magnet and beam re-cogging. With such anticipated
developments we will be able to pursue the open charm and open beauty
*spin physics* measurements at PHENIX with the proposed Silicon Vertex
detector.

### Direct photon + Jet measurement:

One of the limitations of the direct photon measurement that is possible
with existing PHENIX detectors, is an imperfect determination of the
partonic kinematics in the event. The uncertainty in the determination
of the x of the gluon exists because we observe only a single photon in
the final state. Event-by-event reconstruction of the event kinematics
is impossible, and one has to rely on the Monte Carlo simulations to
understand the event kinematics coupled to the detector acceptance. This
has been studied (see section 3.3) using a PYTHIA simulation. The
proposed VTX detector enables the tagging of the hadronic activity
(originating from a single quark/jet), hence determination of the jet
axis (Figure 20), and will significantly reduce the uncertainties
stemming from the reconstruction of the parton kinematics (Figure 21).
Our dependence on Monte Carlos is factored out. Additional uncertainties
related to the determination the total jet energy, remain, however one
does better by tagging the jet with the proposed VTX.

PHENIX's limited acceptance in rapidity as well as azimuth has been a
significant hurdle in our measurement of any jet related physics. The
silicon vertex detector with its good hit resolution and large
acceptance will serve as a high-resolution tracker and provide the much
needed jet axis measurement in co-incidence with the direct photon
measurement. Monte Carlo studies indicate a significantly improved
determination of x-gluon (20% relative compared to \~40% without the
VTX). The VTX detector can also be used to detect charged tracks around
the direct photon candidate. This may allow an improved isolation
selection for the direct photon in the event.

The silicon vertex detector is hence crucial in determining the
polarized gluon distribution using the direct photon channel. For this
particular measurement it converts the PHENIX detector in to a high
resolution - large acceptance detector.

### Other advantages of the Silicon Vertex Detector:

There are other advantages of the silicon vertex detector, which we
mention briefly in this section.

#### Background suppression for W physics event sample 

*W* physics at PHENIX allows a unique possibility to distinguish the
flavor (*u* and *d*) dependence of quark structure function and its
polarization: *W*^+^ is produced by collision of $u + \overline{d}$ ,
while *W*^-^ is produced by $d + \overline{u}$. However, if one wants to
explore *W* physics with electron final states in the central arm,
backgrounds from hadrons can be a significant problem. Improved momentum
resolution and (hence) background suppression is the way to reduce the
background. Using information from the silicon vertex detector in the
momentum reconstruction, the moment resolution is improved by a factor 2
or 3. In addition, the large solid angle coverage of VTX will allow us
to apply an isolation cuts for the single electron candidate and thereby
to improve S/B ratio of the W decay electron. In general, an electron
from W decay is isolated from a jet activity, while the backgrounds
(very high *p*~T~ charged particle decays and high *p*~T~ electrons from
heavy quark decay) have associated jet activity around it.

#### Improved correlation measurements between particles

It is expected that the large acceptance of the silicon vertex detector
in rapidity and azimuthal coverage, will enable us understand
correlations between particles produced in the hadron-hadron collisions.
One important measurement is related to the transversity distribution:
Transversity structure function is as fundamental as any other
(un-polarized and polarized structure function of the nucleon), but it
is yet to be measured. It is a helicity odd object, and it needs to be
measured in experiments as a product of another helicity odd object so
that the product is helicity even. Measurements of this kind involve
measuring many particles and their angular correlations in the final
state in addition to possible hadronic jet activity in the primary
interaction. One example of this is the Collins fragmentation function,
which refers to a correlation between hadron distributions around the
jet axis. The orientation of + - (hadron-) pair is also expected to show
correlation with the transverse fragmentation function in single
transverse spin *pp* scattering at RHIC. The Silicon vertex detector is
expected to improve determination of this orientation in spite of the
fact that lack of particle-ID associated with such an event will dilute
the correlation. Through these correlation functions we plan to measure
the transversity distribution. Needless to say, enhanced acceptance,
resolution provided by the silicon vertex detector would be crucial for
such a measurement.

## 2.3 Exploration of the nucleon structure in nuclei

Proton-nucleus collisions not only provide important baseline
information for the study of QCD at high temperatures, they also address
the fundamental issues of the parton structure of nuclei. Since the
discovery of the EMC effect in the 1980\'s, it is clear that the
parton-level processes and structure of a nucleon are modified when
embedded in nuclear matter[^20]. These modifications reflect fundamental
issues in the QCD description of the parton distributions, their
modifications by the crowded nuclear environment of nucleons, gluons and
quarks, and the effect of these constituents of the nucleus on the
propagation and reactions of energetic partons that pass through them.

Of particular interest is the depletion of low momentum partons (gluons
or quarks), called shadowing, which results from the large density of
very low momentum partons. For gluons at very low momentum fraction, *x*
\< 10^-2^, one can associate with them, following the uncertainty
principle, a large distance scale. These high-density gluons then will
interact strongly with many of their neighbors and by gluon
recombination or fusion are thought to promote themselves to larger
momentum fraction, thus depleting small values of *x*. In most pictures
the overall momentum is conserved in this process and so the small *x*
region gluon density is depleted while the moderate *x* region above
that is enhanced. In recent years a specific model for these processes,
called gluon saturation, has been discussed extensively by McLerran and
collaborators[^21]. Gluon saturation affects both the asymptotic
behavior of the nucleon gluon distributions as *x* approaches zero and
the modification of this behavior in nuclei, i.e. shadowing.

At RHIC energies many of the observables are affected by parton
distributions at small x where nuclear shadowing is thought to be quite
strong. However, theoretical predictions of the amount of shadowing
differ by factors as large as three. For example, in the production of
J/ in the large rapidity region covered by the PHENIX muon arms, models
from Eskola et al (Figure 7) predict only a 30% reduction due to gluon
shadowing, while those of Frankfurt & Strikman[^22] (Figure 8) or
Kopeliovich[^23] predict up to a factor of three reduction. Results from
the measurements of the d-Au run should help to clarify how much
shadowing we have, but increased statistics from higher luminosity runs
and more definitive measurements via observables that are sensitive to
gluon structure functions over several channels will be necessary to
test the theory with sufficient power to constrain the underlying QCD
processes.

![](media/image9.png){width="4.079861111111111in"
height="2.6381944444444443in"}

[]{#__RefHeading___Toc66641778 .anchor}Figure 7 - Gluon shadowing from
Eskola[^24] as a function of x for different Q^2^ values: 2.25 GeV^2^
(solid), 5.39 GeV^2^ (dotted), 14.7 GeV^2^ (dashed), 39.9 GeV^2^
(dotted-dashed), 108 GeV^2^ (double-dashed) and 10000 GeV^2^ (dashed).
The regions between the vertical dashed lines show the dominant values
of x~2~ probed by muon pair production from DDbar at SPS, RHIC and LHC
energies.

In particular, it is clear that a precise knowledge of the shadowed
gluon structure functions in nuclei is essential towards understanding
several of the important signatures for QGP in heavy-ion collisions at
RHIC, including open and closed heavy-quark production. Recombination
models for J/ production, which might cause an enhancement of that
production in heavy-ion collisions due to the large density of charm
quarks created in a collision, must be constrained by an accurate
measurement of the amount of charm produced given the shadowing of the
gluon densities in the colliding nuclei.

A number of other physics issues besides shadowing also need to be
understood. Energy loss of partons in the initial state is thought to
have a small effect at RHIC since the energy loss per fm, in most
models, is thought to be approximately constant and small compared to
the initial-state parton energies at RHIC. On the other hand, partons in
the final state could show some effects of energy loss since their
momentum is lower, while heavy-quarks are expected to lose less energy
than light partons due to the dead-cone effect[^25]. These issues are
very important in the high-density regions created in heavy-ion
collisions, but need a baseline for normal nuclear densities from
proton-nucleus collisions. Another general feature of most produced
particles comes from the multiple scattering of initial-state partons,
which causes a broadening of the transverse momentum (Cronin effect) of
the produced particles.

In general, all processes suitable for the measurement of gluon spin
structure in nucleons are also ideal for probing the gluon distributions
in nuclei. The reach in Bjorken *x* is indicated in Figure 8,
superimposed on calculations of the ratio of nuclear to nucleon gluon
structure functions.

![](media/image10.png){width="4.034722222222222in" height="3.15625in"}

[]{#__RefHeading___Toc66641779 .anchor}Figure 8 - Gluon shadowing
predictions along with PHENIX coverage. The red bars indicate the
additional range provided by the vertex upgrade, while the blue bars
cover the PHENIX baseline. The three theoretical predictions are for
different Q transferred, blue, green and red lines are Q = 10, 5 and 2
GeV/c respectively, from Frankfurt and Strikman[^26].

The red bars indicate the additional coverage provided by the vertex
upgrade compared to the baseline of PHENIX. The vertex upgrade extends
the *x*-range from the anti-shadowing region into the shadowing domain
and therefore will provide a measurement of shadowing and establish the
shape of the shadowed structure functions versus *x*.

Drell-Yan measurements, which provide a direct measure of the anti-quark
distributions in nucleons or nuclei, have always been limited in the
past in their reach to low *x* by the inability to separate the
Drell-Yan muon pairs below the J/ in mass from copious pairs from
open-charm decays in that mass region. For example, in FNAL E866/NuSea,
information extracted from the Drell-Yan process was limited to masses
above 4 GeV.

![](media/image11.png){width="4.843055555555556in"
height="2.3361111111111112in"}

[]{#__RefHeading___Toc66641780 .anchor}Figure 9 - Dimuon mass spectrum
from E866/NuSea[^27] showing the mass region used in their analysis
which excludes masses below 4 GeV. Lower masses were excluded because of
the large backgrounds from open charm in that region.

On the other hand, PHENIX, with the addition of a vertex detector,
should be able to identify and quantify the portion of the lower mass
dimuon continuum from charm decays and therefore isolate the Drell-Yan
process at these lower mass and lower *x* values. In the
central-rapidity barrel region values as low as *x~2~* \~ 0.7x10^-2^
could be accessed. This will still be a challenge because of the small
cross sections and yields for Drell-Yan at RHIC, but has the potential
of providing information on the anti-quark distributions at much smaller
values of *x*. At the same time one would also learn more about charm
production and the correlation of the charm pairs through the charm
pairs found in the continuum.

In summary, the silicon vertex barrel, which covers the PHENIX central
arm mid-rapidity range ( \|*y*\| \< 0.35 ), addresses the following
physics in dA reactions :

-   Charm and beauty at high p~T~ and mid-rapidity via high-*p~T~*
    electrons and also exclusive decays such as $D \rightarrow K\pi$ and
    $D \rightarrow K\text{ππ}$.

-   A gluon structure measurement in the anti-shadowing region as a
    baseline for shadowing measurements at small *x*.

-   Charm measurements at mid-rapidity as a baseline for J/ production,
    i.e. for comparisons of open and closed charm which should share the
    same initial-state effects in nuclei.

-   Accurate measurement of nuclear dependence of charm cross section

-   Beauty cross sections at mid-rapidity as a constraint on the
    contributions of $B \rightarrow \frac{J}{\psi}$to J/production.

-   Comparison of light and heavy-quark *p*~T~ distribution to determine
    differences in energy loss and Cronin effects.

-   Better separation in high-luminosity measurements of measurements of
    the three states.

-   Low-mass electron pairs and anti-quark shadowing at small *x*
    values.

For many of these topics the physics picture that can be obtained is
significantly strengthened with the planned addition of an end-cap
silicon vertex detector as described in Appendix A.

# 3. Physics measurements with the VTX detector

## 

The proposed VTX detector provides us the tool to measure new physics
observables that are to date not accessible at RHIC or available only
with very limited accuracy. These include a precise determination of the
charm production cross section and transverse momentum spectra -
particularly at high *p*~T~, a measurement of beauty, and the detection
of recoil jets in direct photon production. In this section, we discuss
how the proposed VTX detector makes these measurements possible, or
significantly improves our capability to address these observables.

Before discussing the simulation results and the expected performance of
the VTX for each of the observables, we briefly explain the design of
the proposed VTX detector and discuss the required performance. More
technical details of the implementation of the VTX detector are
presented in the section 4. In the last sub-section, we summarize the
expected rate of physics signals and the physics reach that will become
available with the VTX detector.

## 3.1 Design Considerations and the VTX detector geometry

### Design Considerations

The design considerations for the detector are

-   ability to match tracks reconstructed in the central arms to hits or
    track segments from the silicon vertex detector.

    -   sufficient position accuracy so that the displacement resolution
        of the track with respect to the collision point is less than
        the c of charm and beauty decays, i.e. a resolution less than
        100m, preferably at the level of 30-50 m.

    -   high resolution predominantly in r direction, i.e. the main bend
        plane of the magnetic field, matched to the central arm
        resolution.

A variety of simulations and first principle calculations have shown
that the displacement resolution is dominated by the position accuracy
of the two inner most detector layers and by the amount of
multiple-scattering between the collision point and the two position
measurements. Assuming that the multiple scattering occurs at the
location of the first layer, the Distance to the Closest Approach (DCA)
of a trajectory to the beam axis in the main bend plane can be measured
with a resolution given approximated by:

$$\sigma^{2_{\text{DCA}}} \approx \frac{\left( \sigma_{1^{2}}r_{2}^{2} + \sigma_{2}^{2}r_{1}^{2} \right)}{(r_{2} - r_{1})^{2}} + \theta_{\text{ms}^{2}}\frac{r_{1}^{2}}{\text{sin}^{2}\theta}$$

Here , and *r*~1~, *r*~2~ are the *r* resolution and radial position of
the first and second layer, respectively. The average
multiple-scattering angle, denoted by ~ms~, is given by the beam pipe
thickness and the first detector layer. The first term quantifies the
contribution due to the finite position resolutions, while the second
term is the effect of the multiple scattering. Given standard silicon
detector segmentation of 50 to 100 m in *r* and a typical thickness of 1
to 2 % of a radiation length, both terms contribute to the final
resolution. For our \"strawman\" layout of the VTX, which is discussed
below, typical DCA resolution from this estimate is \~ 40 m: a value
confirmed by detailed simulations.

It is evident from the equation for the DCA resolution that in order to
minimize the DCA resolution, the first layer should be as close to the
collision point as is practical, which at RHIC is about 2 cm, and the
first layer plus beam-pipe should be as thin as possible.

![](media/image12.png){width="2.901388888888889in"
height="2.825in"}![](media/image13.png){width="2.825in"
height="2.825in"}

[]{#__RefHeading___Toc66641781 .anchor}Figure 10 (a) Cross section of
the silicon vertex tracker (VTX) along the beam axis. The inner pixel
hybrid layer is located at a radial distance of 2.5 cm from the beam
pipe and extends over \~22cm in beam direction. The silicon strip outer
layers are located at 6, 8 and 10 cm. All three extend over \~26 cm in
beam direction. The Be beam pipe with 2 cm radius is also shown. (b) Cut
through the silicon vertex detector in the xy-plane transverse to the
beam axis. The VTX is assembled in two half shells with small acceptance
gaps at top and bottom. The different layers of each half shell have 5,
7, or 9 rows of silicon detectors, depending on the radial location of
the layer.

### VTX detector geometry

After exploring different configurations, we decided to perform all
feasibility studies with the detector layout depicted in Figure 10. The
layout features four concentric barrels of silicon detectors with a
length of approximately 30 cm along the beam axis. The outer three
barrel layers are silicon strip detectors placed at radial positions of
*r~4~*=10 cm (barrel 4), *r~3~*=8 cm (barrel 3), and *r~2~*=6 cm (barrel
2). The inner barrel is composed of a silicon pixel device and is
located at *r~1~*=2.5 cm (barrel 1). The beam-pipe has a design radius
of 2.0 cm and is made of 500 m thick Be.

The pixel detectors for the inner barrel layer have a segmentation of 50
m by 425 m. The outer layers are assumed to have 80 m 3cm strips. This
choice together with the radial location guarantees that the occupancy
of the innermost strip layer (barrel 2) remains about 10% even in
central Au-Au collisions. In the low occupancy environment of pp
collisions a stereoscopic readout of the strip layers reduces the
effective channel size to 80m 1000m.

These detectors have been implemented as our \"strawman design\" into
the GEANT simulation of the PHENIX detector. At this point no details of
cooling, mechanical support, cables etc. are put into the simulation,
however these materials are approximated by an effective thickness of
the detector layers. From a survey of existing silicon detectors we
conclude that a thickness of 2% of a radiation length per layer should
be easily achievable while 1% of a radiation length will be challenging.
We have chosen these two values for this effective thickness, 1% and 2%
of a radiation length, to bracket the potential range of thickness and
performed simulations with both values.

### Detector Occupancy

The occupancy of the each layer is calculated by using a GEANT model of
the VTX detector integrated into the standard PHENIX simulation program,
PISA. We use HIJING event generator to generate central Au+Au collision
event, and feed the generated events into PISA with the VTX detector. In
the simulation, we use a simplified model of the VTX signal generation.
Charge sharing among the pixels and strips is accounted by the length of
track segment projection onto the pixel or strip area. In this
simplified simulation, no effect from charge diffusion in the sensor is
taken into account. Since the size of charge diffusion (\~ 10 m) is much
smaller than the strip width (80 m), the dominant part of charge sharing
effect is included in the simulation.

[]{#__RefHeading___Toc66641830 .anchor}Table 1 Occupancy of the VTX
layers for central Au+Au collisions at 200 GeV. HIJING event generator
and a GEANT model of the VTX detector is used to calculate the
occupancy.

  ---------- ---------- ------------ ------------------ ------------------
  layer      radius     Detector     Occupancy          

  Layer 1    2.5 cm     Pixel        0.53 %             

  Layer 2    6.0 cm     Strip        10.8% (x-strip)    11.6% (u-strip)

  Layer 3    8.0 cm     Strip        6.6 % (x-strip)    7.0% (u-strip)

  Layer 4    10.0 cm    Strip        4.5 % (x-strip)    4.7 % (u-strip)
  ---------- ---------- ------------ ------------------ ------------------

The result of the simulation is summarized in Table 1. The occupancy is
lowest at about 0.5% for the first pixel layer. The second layer, or the
first strip layer, has the highest occupancy of about 11%. The
calculated occupancy is about twice of the value if there is no charge
sharing effect.

The rather high value of occupancy at the second layer, shown in the
table, is a concern. This can undermine our ability of a clean DCA
measurement in the highest multiplicity events of Au+Au collisions due
to ambiguity of the track finding. However, since the VTX simulation
software is still under development and therefore we presently can not
quantitatively evaluate the impact of the occupancy to the DCA
measurement. Although the second layer has a relatively high occupancy,
the occupancy is lower in the outer two layers and it is very small in
the first pixel layer. In the present design, there are total of 3 strip
layers and 1 pixel layers, i.e. it is redundant with respect to track
finding, in particularly within the acceptance of the PHENIX Central
arm. Since the DCA measurement minimally requires two layers, the two
extra Silicon strip layers in the present design provide redundancy as
well as the standalone tracking needed in the -jet measurement. Using
information from all four layers will permit appropriate cuts in the
tracks so that the backgrounds and inaccurate measurements of the DCA
due to the high occupancy at the first strip layer can be substantially
reduced.

We are currently finalizing the detector configuration based on the
simulation. One possible alternative configuration is to reduce the
number of strip layers from 3 to 2, and then to expand the radius of the
strip layers. Using the same number of Silicon sensors and read-out
chips, the detector can be re-configured to have 2 strip layers at R=10
cm and R=14 cm. In this configuration, the occupancy of the inner strip
layer at R=10 cm is only 4.5%, and the outer layer is only 2.3%. This
configuration does not have the high occupancy problem of the straw-man
design, but it lack one layer of redundancy. A detailed Monte Carlo
study is required to determine the relative merit of the two detector
models. Substantial progress is being made on a realistic reconstruction
software chain of the VTX detector. We will study the performance of the
VTX detector in several configurations, including the present design and
the alternative configuration described here. We will decide the
optimized configuration of the detector by summer 2004 based on the
simulation study.

### Central Track -- VTX matching

In order to make full use of the VTX capabilities, tracks reconstructed
in the central arms have to be matched to hits or track segments in the
VTX. In the following we estimate the fraction of ambiguous track
matches for the most difficult case, namely for central Au-Au collisions
at 200 GeV. For *pp* or more peripheral Au-Au collisions track matching
should not be a problem.

In central Au-Au collisions the charged particle density has been
measured and is *dN/d* \~ 600 at =0. In the following we double this
number to account for hit splitting, noise, and background hits. In the
pixel detector the occupancy then is about 0.7% per pixel or 0.2 hits
per milli-steradian. This is a conservative estimate. We expect that
merging hits to clusters can eliminate the effect of hit splitting and
that most of the noise and background hits can be removed by correlating
information from several planes. Thus, more optimistically the hit
density may be closer to 0.1 per mili-steradian and consequently the
following occupancy estimates may be reduced by a factor 2.

The pointing resolution of reconstructed tracks in the central arm
spectrometers is well known. It is given by the performance of the drift
chamber, which has a single point spatial resolution of 150 m in azimuth
and 2 mm in inclination. Providing a reference point, *P*, at a
reference radius, *R*, in the drift chamber active volume, an angle in
the bend plane, , can be defined as the angle between a straight line
projection from the collision vertex to *P*, and the bend plane vector
of the reconstructed track at *P*. The momentum (in GeV/c) of a track is
related to by *p* = 87 mrad GeV/c / . Here, 87 mrad GeV/c is the
effective field integral, *K*~1~, of the trajectory to point *P*.
Utilizing this relationship, the momentum resolution can be related to
the intrinsic angular resolution of the drift chamber, and the angular
resolution due to multiple scattering from the collision vertex to point
*P*, ~ms~, as:

$\left( \frac{\delta p}{p} \right)^{2} = \left( \frac{\sigma_{\alpha}}{K_{1}}p \right)^{2} + \left( \frac{\sigma_{\text{ms}}}{K_{1}\beta} \right)^{2}$

Using the measured widths of distributions of the square of the
reconstructed mass for identified protons, pions, and kaons, as a
function of momentum, the values of and ~ms~ have been extracted from a
simultaneous fit of all three of these particle species from the RHIC
200 GeV run. The fit result yields = 0.86 mrad and ~ms~ = 0.84 mrad,
averaged over positive and negative particles. The results are
independent of centrality. Added in quadrature, the bend-plane angular
resolution is 1.20 mrad. The angular resolution of the drift chamber in
the non-bend plane is 2.70 mrad if the information from the event vertex
is used; here the *z* resolution of the PHENIX beam-beam counter, which
is 6 mm, was assumed for the vertex.

We assume that in central Au-Au collisions the VTX information will
allow to determine the interaction point to better than 1010 m^2^ in the
bend-plane and to better than 50 m along the beam direction. With this
vertex accuracy the VTX determines the original direction of the track
with an uncertainty of 0.7 mrad in azimuthal and 5 mrad inclination
direction. To match the central tracks in angular space we need to
account for the central track resolution and multiple scattering in the
4 silicon layers (assume 2% X~0~ per layer and 1 GeV/c momentum). If we
assume 2 matching window the search area is 8 mrad in azimuth and 12
mrad in inclination. The solid angle of this search area is 0.384
milli-steradian and thus the expected random match probability is 7.8%.
Requiring hits from the different VTX layers will reduce the random
match.

This estimate is based on the vertex position and the hit information
from the pixel detector. If tracks or track segments can be
reconstructed in the VTX, the number of random matches can be further
reduced. The reduction will depend on the level of track reconstruction
in central collisions that will be possible with the VTX alone. Any
tracking will reduce the number of hits in the pixel detector to a
smaller number of tracks. Basic track reconstruction will allow charge
matching and more sophisticated analysis may even allow momentum
matching to the central arms. Quantification of the potential reduction
requires detailed Monte Carlo studies which are under way.

## 3.2 Open Charm and Beauty Measurement

### Open Charm measurement from semi-leptonic decay

Open charm and beauty spectra and yields are a sensitive probe of the
early stages of heavy-ion collisions, and are keys for the physics goals
of gluon spin structure and for structure function studies in *pA*
reactions. For heavy-ion collisions, the goal is to improve the accuracy
and precision of the charm measurement, and to extend the reach to
higher *p*~T~ to measure the energy-loss of open charm. The yield of
beauty in heavy-ion collisions should be dominated by the initial hard
collisions and hence will serve as a critical benchmark for the first
stage of reaction.

For open charm our strategy is to use semi-leptonic decays to electrons
in a wide *p*~T~ range and to complement this at high *p*~T~ with
hadronic decay channels. The four layers of the central silicon barrel
provide an accurate measurement of the trajectory and impact parameter
of tracks near mid-rapidity. Single electrons at different momenta were
simulated and tracked through the GEANT implementation of PHENIX
including the straw-man vertex detector. The simulation was run assuming
zero magnetic field. The hits from the electrons were tracked back to
calculate the transverse distance-of-closest approach (DCA) to the known
point-of-origin. For all cases the DCA resolution is better than or
comparable to the c of charm and beauty decays.

![](media/image14.jpeg){width="4.024305555555555in"
height="3.8090277777777777in"}

[]{#__RefHeading___Toc66641782 .anchor}Figure 11 DCA distribution for
electrons from Dalitz, charm and beauty decays simulated through four 1%
Si layers on the left and four 2% layers on the right.

The power of this resolution is seen by comparing the distribution of
DCA from charm, beauty and Dalitz decays of ^0^ in Figure 11. The
spectra were generated from p+p events (PYTHIA) passed through GEANT.
The design thickness for the inner pixel layer is 1% of radiation length
(X~0~) and for the outer barrel layers is 1.7% X~0~. Hence for these
simulations we bracket the range of possibilities by running simulations
with either 1% or 2% X~0~ per layer. In the bottom panels of Figure 11
are the DCA distributions for electrons above 1 GeV/c. A DCA cut of 200
m removes the majority of Dalitz contribution from the electron yield.
Note that this is the momentum of the electron and given the large
Q-value of the *D*-decay, these electrons predominantly come from
low-momentum *D*'s. Since beauty decays have longer lifetimes, the
electrons from *B* decays dominate at large DCA values. By fitting the
full DCA distribution with the expected shapes from the different c we
should be able to simultaneously extract integrated charm and beauty
yields for electron momenta above 1 GeV/c.

Below 1 GeV/c the extraction is more difficult, but even down to 500
MeV/c charm dominates the DCA distribution above 200 m for a thickness
between 1 and 1.5% of a radiation length. In particular, the vertex
detector will provide a dramatic improvement over the previous
measurement^15^, which was limited to 40% systematic error resulting
from the uncertainties in the background subtraction. Figure 12 shows
the "signal to noise" for the optimistic (1% X~0~) and pessimistic (2%
X~0~) cases compared to the measurement without the vertex detector
available. This should allow a much cleaner extraction of the
background-subtracted electron spectra for *p*~T~\>0.4 GeV/c than was
previously available, including the charm-specific *d^2^N~e~/dydp~T~*
for electrons up to about 2.5 GeV/c.

![](media/image15.wmf){width="4.0in" height="2.8826388888888888in"}

[]{#__RefHeading___Toc66641783 .anchor}Figure 12 Signal to Background
ratios as a function of minimum electron p~T~ cut. The signal
corresponds to detached electrons from charm decays using a DCA cut of
200m (circles) or no DCA cut (diamonds). The background corresponds to
electrons from Dalitz decays and photon conversions which pass the
corresponding DCA cuts, assuming four layers of Silicon with 1 or 2% of
a radiation length per layer.

Figure 13 shows that there is a useful correlation between the *p*~T~
cut applied to the electrons and the *p*~T~ of the parent *D* meson. The
points represent the most probable value of the parent *p*~T~ while the
error bar represents the FWHM spread. Using the correlation, one can,
for example, determine the *p*~T~ distribution of the parent *D*-meson
from the decay electron spectrum.

.

![](media/image16.wmf){width="4.472916666666666in"
height="3.2104166666666667in"}

[]{#__RefHeading___Toc66641784 .anchor}Figure 13 Correlation between the
transverse momentum of the D mesons and the minimum p~T~ cut applied to
the electrons (using a DCA cut of 120m). The points represent the most
probable value of the D meson p~T~ while the spread represents the
(asymmetric) full width at half maximum.

### Direct Measurement of *D^0^K^-+^* at high *p~T~*

For higher values of the electron *p*~T~, electrons from *B*-decays
dominate those from *D*-decay and the extraction of the charm
contribution becomes difficult. This can be overcome by a direct
measurement via hadronic decay channels, which only becomes possible
only at high *p*~T~ because of the small solid angle of the central arm
spectrometers of PHENIX.

![](media/image17.png){width="2.977777777777778in"
height="2.0027777777777778in"}![](media/image18.png){width="2.977777777777778in"
height="2.0027777777777778in"}

[]{#__RefHeading___Toc66641785 .anchor}Figure 14 The DCA distributions
in cm for pions with the inner pixel having 1%X~0~ thickness. On the
left is the DCA for direct pions with pt \>1 GeV/c and on the right is
the DCA for pions from *D*^0^ decay.

We have simulated *D*^0^ production using *p+p* PYTHIA events and
tracked them through GEANT as described above. The decay pions and kaons
where then compared to those directly produced in a central Au+Au
background event. Figure 14 shows the DCA distribution for directly
produced pions with a *p*~T~ cut of 1 GeV/c compared to the DCA
distribution for pion daughter particles from *D*^0^ where the parent
*D*^0^ has *p*~T~ above 2 GeV/*c*. The pions from *D*^0^ have a broader
DCA distribution than directly produced pions. Clearly a DCA cut will
remove a larger fraction of the direct pions than pions from *D*^0^
decay.

We have estimated the signal/background (S/B) for a *D*^0^ analysis for
central Au-Au collisions where the S/B is the smallest. In this study
only *D*^0^s with *p*~T~ above 2 GeV/c are were used to better match the
opening angle of the daughters to the PHENIX acceptance. We require that
both the pion and kaon from the decay fall into the acceptance and that
they have not decayed before reaching the outer tracking detectors. We
also assume that kaons are identified by one of the PHENIX PID
detectors, an aerogel plus TOF detector covering the full acceptance of
the west arm, and the existing TOF detector in the east arm. Lifting
this requirement will deteriorate the signal/background by roughly a
factor of 5, depending on the p~T~ of the kaon and the centrality of the
event.

![](media/image19.png){width="2.977777777777778in"
height="2.0027777777777778in"}

[]{#__RefHeading___Toc66641786 .anchor}Figure 15 The invariant mass
distribution for background pairs from central Au+Au events. Each
pion+kaon pair has a pair p~T~ \> 2 GeV/c.

Figure 15 shows the invariant mass for combinatorial background from
pions kaons pairs that have a pair *p*~T~ \> 2 GeV/*c*. Only a few
percent of the combinatorial pairs have an invariant mass near the
*D*^0^ mass of 1.86 GeV. We count the background in a 40 MeV window
around 1.86 GeV. The window corresponds to 2times the rms mass
resolution, which is 1% calculated from the known momentum resolution of
the PHENIX tracking.

To count the signal we scale the number of reconstructed *D*^0^\'s in
the PYTHIA events by the number of binary collisions for a central Au+Au
events. The signal/background (*S/B)* is then studied as a function of a
simultaneous DCA cut on the pions and kaons. Figure 16 shows the *S/B*
for different DCA cuts on pairs detected in the west-arm. The left- and
right-hand panels are for simulations with 1% X~0~ and 2% X~0~ per
layer. With no DCA cut the *S/B* is less than 0.1%, placing a DCA cut of
100m increases the *S/B* to a level of 2-3%. This *S/B* should be
further improved by requiring that the parent particle point back to the
collision vertex.

The statistical significance of the signal can be estimated by
$\frac{S}{\sqrt{B}}$. This ratio can be interpreted as the number of
sigma of the extracted counts in the signal over the fluctuating
background. It increases with the square root of the number of events.
Using the run assumptions described in section 3.5, we will
approximately collect 200M central Au+Au events within a 10 cm collision
window in a running period. Under these assumptions the combined
(*D*^0^+*D*^0^) S/B for different DCA cut strategies for pairs detected
in the west-arm of PHENIX is shown in Figure 17.

![](media/image20.png){width="2.977777777777778in"
height="2.0027777777777778in"}![](media/image21.png){width="2.977777777777778in"
height="2.0027777777777778in"}

[]{#__RefHeading___Toc66641787 .anchor}Figure 16 The *S/B* for D^0^K
with a pt \>2 GeV/c for central Au+Au events into the west-arm of
PHENIX. On the left is the simulation for 1%X~0~ thickness per layer. On
the right is simulation for 2%X~0~ thickness per layer.

![](media/image22.png){width="2.977777777777778in"
height="2.0027777777777778in"}![](media/image23.png){width="2.977777777777778in"
height="2.0027777777777778in"}

[]{#__RefHeading___Toc66641788 .anchor}Figure 17 The S/B for
D^0^+D^0^-\>K with a pt \>2 GeV/c for central Au+Au events into the
west-arm of PHENIX. On the left is the simulation for 1%X~0~ thickness
per layer. On the right is simulation for 2%X~0~ thickness per layer.

From Figure 17, we can conclude that the D^0^ peak for particles above
p~T~ \> 2 GeV/c can be extracted robustly. This is the worst case for
the most central collisions where the combinatorial background is
largest. Requiring the parent to point to the collision vertex can
further reduce the background.

Simulations indicate that at higher-pt the acceptance for D^0^ increases
since the opening angle between the daughters is smaller. The background
due to combinatorics decreases. For D^0^s above p~T~ \> 3 GeV/c, even
though the open charm yield is lower, the significance of the
(*D*^0^+*D*^0^) peak maintains a level of 7sigma in central Au+Au
collisions.

### Open Beauty Measurement

*B* meson production, while more rare than *D* production, is somewhat
simpler to measure with the VTX detector because of the larger *c*. The
main challenge is the relatively low rate. We have at least two methods
to measure *B* with the VTX detector:

-   Semi-leptonic decays: Since beauty mesons have a larger lifetime
    than charm mesons, it is possible to extract the beauty yield at low
    transverse momentum from the distribution of decay distances. At
    large transverse momentum beauty decays dominate the DCA
    distribution.

-   The decay channel *B* J/produces J/ that are displaced from the
    collision.

For momenta greater than 3 to 4 GeV/*c* electrons with displaced
vertexes are dominated by beauty decays. This is clearly seen in Figure
18. By placing a DCA cut on the order of 150 m we should be able to
cleanly separate electrons from beauty from all other sources. Note
however that this clean separation is only possible with the VTX
detector even in this high *p*~T~ region. Although the high *p*~T~
region is dominated by beauty, there is a significant contribution from
charm component, and the separation of these two components is possible
only with the DCA measurement. With an accurate determination of the *b*
component, the charm component will also accessible up to 6 GeV/*c*
using a simultaneous fit of the DCA distribution. As discussed in the
previous section, the high *p*~T~ charm component will also be measured
directly in *DK* decay.

The signal to background ratio for beauty decays at high momentum is
shown in Figure 19. The effect of the DCA cut is even more favorable
than for charm.

![](media/image24.jpeg){width="4.152777777777778in"
height="4.245833333333334in"}

[]{#__RefHeading___Toc66641789 .anchor}Figure 18 DCA distribution for
electrons from Dalitz, charm and beauty decays simulated through four 1%
or 2% Si layers

![](media/image25.wmf){width="4.188888888888889in"
height="3.0180555555555557in"}

[]{#__RefHeading___Toc66641790 .anchor}Figure 19 Signal to Background
ratios as a function of the minimum electron p~T~ cut. The signal
corresponds to detached electrons from beauty decays using a DCA cut of
200m (circles) or no DCA cut (diamonds). The background corresponds to
electrons from Dalitz decays and photon conversions which pass the
corresponding DCA cuts, assuming four layers of Silicon with 1 or 2% of
a radiation length per layer

## 3.3 Photon and jets measurement in polarized p+p

Direct photon emission a key process to measure the gluon distribution
of the nucleon and the polarization of the gluons. At RHIC energies,
quark-gluon Compton scattering, *q*+*g* *q*+ is the dominant
parton-level process in the production of high p~T~ direct photons. In
*pp* collisions the cross section of this process is directly
proportional to the quark and gluon densities multiplied by the pQCD
cross section. Thus measuring the direct photon together with the recoil
jet is a direct and clean way to measure the gluon density and
polarization as function of the momentum fraction *x*. With the present
PHENIX setup, direct photons are measured with the finely segmented
electro magnetic calorimeters (EMCal) in the central arms. However, due
to the limited coverage of the central arm tracker, most of the recoil
jet cannot be measured. Therefore we can only measure the direct photon
averaged over the recoil jet kinematics.

In *p+p*, *p+A*, and light ion collisions, the VTX detector works as a
stand-alone, large solid angle charged particle tracker. The expected
momentum resolution for tracks reconstructed solely by the VTX detector
is about 10% for a 1 GeV/*c* track. This resolution is sufficient to
reconstruct the recoil jets in wide rapidity range (\|\|\<1). With the
knowledge of the recoil jet we can constrain the initial kinematics
(*x*~1~ and *x*~2~) of incoming partons and thus determine the gluon
density and polarization as function of *x*.

We have studied the potential improvements due to the VTX detector in a
Monte Carlo simulation. In the simulation, the direct photon events have
been generated using the PYTHIA event generator. The recoil jet is then
reconstructed from the charged tracks within the VTX detector acceptance
(\|\|\<1.2) but in opposite azimuthal direction of the direct photon. In
the first step of the algorithm, tracks with momentum greater than 1
GeV/*c* at an azimuth angle opposite to the direct photon *(\| -- \| \>*
*/2*) are selected. Then, the direction of the jet is estimated as the
momentum weighted average of the selected tracks, as

$$\eta^{\text{jet}} = \frac{\sum_{}^{}{\eta^{i}p_{T}^{i}}}{\sum_{}^{}p_{T}^{i}},\varphi^{\text{jet}} = \frac{\sum_{}^{}{\varphi^{i}p_{T}^{i}}}{\sum_{}^{}p_{T}^{i}}$$

Next, the tracks with momenta above 1.0 GeV/c and within the cone of
radius
$R = \sqrt{(\eta^{\text{jet}} - \eta^{i})^{2} + (\varphi^{\text{jet}} - \varphi^{i})^{2}} < 0\text{.}5$are
selected. In a second iteration the recoil jet axis is corrected with
the same algorithm, using the tracks within the cone. This procedure is
iterated until the direction of the axis no longer changes.

![](media/image26.png){width="5.897916666666666in"
height="4.351388888888889in"}

[]{#__RefHeading___Toc66641791 .anchor}Figure 20 In each panel, the
green histogram shows the pseudo-rapidity, ~q~-distribution of the final
hard scattered partons, which initiated the recoil jet; the blue
histogram shows the ~q~-distribution of recoil jets within the barrel
VTX acceptance; and the red histogram show the (^jet^
-~q~)-distribution, where ^jet^ is for the pseudo-rapidity reconstructed
for the recoil jets. Different panels are for the event samples with
direct photon of different transverse momenta, starting from 4-5 GeV/c
in the upper left to 9-10 GeV/c in the lower right panel.

Figure 20 illustrates how well the direction of the recoil jet is
determined by this simple algorithm. In the figure, the pseudo-rapidity
*~q~* of scattered quark (obtained from the event generator) are plotted
as green histograms. The blue histograms in the figure show the
distributions of *~q~* for events in which the recoil jet is
reconstructed within the VTX acceptance. The red histograms show the
difference *~q~ - ^jet^* between the true pseudo-rapidity of the recoil
quark and that of reconstructed jet. The large uncertainty of the recoil
jet kinematics, as seen from the wide distribution of *~q~*, is much
reduced by the reconstruction of the recoil jet direction.

From the measurement of *^jet^* and the transverse momentum *p~T~* of
the direct photon, the kinematics of the initial partons can be
determined. Under the assumption that the *p~T~* of the direct photon
and the recoil jet is the same, the fractional momenta of initial
partons *x*~1~ and *x*~2~ are determined from the following relations:

$$\begin{array}{r}
x_{1} + x_{2} = \frac{2}{\sqrt{s}}(E^{\text{jet}} + E^{\gamma}) = \frac{2p_{T}}{\sqrt{s}}(\text{cosh}(\eta^{\text{jet}}) + \text{cosh}(\eta^{\gamma})), \\
x_{1} - x_{2} = \frac{2}{\sqrt{s}}(p_{Z}^{\text{jet}} + p_{Z}^{\gamma}) = \frac{2p_{T}}{\sqrt{s}}(\text{sinh}(\eta^{\text{jet}}) + \text{sinh}(\eta^{\gamma}))
\end{array}$$

Thus *x~1~* and *x~2~* are calculated as

$$\begin{array}{r}
x_{1} = \frac{p_{T}}{\sqrt{s}}(\text{exp}(\eta^{\text{jet}}) + \text{exp}(\eta^{\gamma})), \\
x_{2} = \frac{p_{T}}{\sqrt{s}}(\text{exp}( - \eta^{\text{jet}}) + \text{exp}( - \eta^{\gamma}))
\end{array}$$

![](media/image27.wmf){width="2.595833333333333in"
height="2.5833333333333335in"}![](media/image28.wmf){width="2.5680555555555555in"
height="2.5680555555555555in"}

[]{#__RefHeading___Toc66641792 .anchor}Figure 21 Correlation between x
reconstructed and true *x*-value from PYTHIA. In the plot on the left,
![](media/image1.wmf) and no jet information has been used. The plot in
the right panel is obtained, using the reconstructed jet axes in the
barrel VTX.

The two panels of Figure 21 shows the correlation between the
reconstructed *x* and its true value known from the event generator. If
the recoil jet direction is not known, left panel, the best estimate for
*x* based on the photon p~T~ is only loosely correlated to the true *x.*
However, with the recoil jet reconstruction, right panel, there is a
narrow correlation between the reconstructed *x* and its true value.

How well initial parton kinematics, *x~1~* and *x~2~*, can be extracted
is summarized by Figure 22. Here, the widths (RMS) of *x*(true) *--
x*(reconstruct))/*x*(true) are shown as function of *x~1~*. In the range
of *x*\>0.04, the x-values are determined with an accuracy of \~20%. The
respective accuracy for the measurements without knowledge of the jet
axis deteriorates by a factor \~2 to 3.

![](media/image29.png){width="4.145833333333333in" height="3.875in"}

[]{#__RefHeading___Toc66641793 .anchor}Figure 22 The relative widths
(RMS) of the (x(true) -- x(reconstruct))/x(true) distributions, using
the reconstructed jet axes in the barrel

## 

## 3.4 Improved momentum resolution and pt resolution

In the present PHENIX detector, drift chambers that are located outside
of the central magnet measure the momentum of the charged particles.
Since there is little magnetic field at the location of the drift
chambers, charged particles traverse them on almost straight
trajectories. As discussed in 3.1 the momentum *p* of a particle is
related to the bend angle measured at the drift chamber approximately as
87 mrad/*p* for *p* in GeV/c.

The momentum resolution of the central detector will be much improved
with the VTX detector. This is because in the present PHENIX central arm
spectrometers the effective field kick of 87 mrad GeV/c is only about
40% of the total angular deflection in the magnetic field. The field
integral at the location of the drift chamber is about 0.7 Tm, which
gives mrad */p.* Since the VTX measures the initial direction of the
particles the full value of is measured rather than the angle at the
edge of the magnetic field. In addition, a second field coil, which has
been installed in 2003, allows increasing the field integral to roughly
1 Tm. With this field integral the total field kick increases to 300
mrad GeV/c. The improvement in momentum resolution is directly given by
the ratio of the field kicks 300 mrad / 87 mrad \~ 3.

The higher momentum resolution with the VTX detector will improve the
high *p*~T~ measurements. At present, a momentum resolution of about
1%/*p* has been achieved. With the VTX detector, the resolution of a 30
GeV/c track can be reduced from 30% to about 10%. In addition, the track
confirmation close to the vertex provided by the VTX will eliminate the
decay and conversion background, which currently limits the *p*~T~ reach
of the PHENIX charged particle tracking to *p*~T~ \< 10 GeV/*c*.

The improvement of the momentum resolution may have a significant impact
on the data quality in the higher e^+^e^-^ mass region around the
states. With the better momentum resolution also the mass resolution
decreases to a level that the members of the family, the resonances ~1S~
(9.46 GeV), ~2S~ (10.02 GeV) and ~3S~ (10.36 GeV) can be clearly
separated. This is shown schematically in Figure 23. The VTX together
with the increased magnetic field reduces the resolution at the states
from \~170 MeV to \~60 MeV for the e^+^e^-^ decay channel, thus allowing
to separate the individual states. We note that this measurement will be
a significant challenge and only possible if sufficiently high
luminosities expected for RHIC II are available for extended running
periods.

![](media/image30.png){width="4.4944444444444445in"
height="3.0430555555555556in"}

[]{#__RefHeading___Toc66641794 .anchor}Figure 23 - Separation of Upsilon
states in the di-electron spectrum with a vertex detector (yellow) and
without (black). The number of s in this plot represents our expectation
for a Au-Au run with a recorded effective luminosity of \~1 nb^-1^ (see
chapter 3.5).

## 

## 3.5 Event rate estimates

In this section we estimate the event rates of selected physics
processes corresponding to the major goals of the VTX detector. First,
we summarize the common assumptions that go into estimating yields for
the physics signals that the VTX detector will make available. We start
with integrated luminosity estimates, based on the luminosity evolution
at RHIC expected by the BNL Collider Accelerator Division. Then we fold
in estimates of all of the practical efficiency factors that reduce the
yields measured by PHENIX. The obtained "effective luminosity" is then
used to estimate the signal yields.

The efficiency factors are summarized in Table 2 for the p-p, d-Au and
AuAu cases. The first three factors, (1) to (3), are the factors that
reduce the CA-D delivered luminosity to the recorded luminosity that is
written on data tape by PHENIX, and therefore they are common for all
three beam species. These factors are based on the actual performance of
RHIC and PHENIX during RUN2 and RUN3, and to be conservative we assume
no improvements of these factors in the future. The largest loss of the
recorded luminosity comes from the vertex cuts, factors (1) and (2) in
the table. Here we used longitudinal length of the collision diamond of
=20cm and a vertex cut of \|z\|\<10 cm since the inner-most layer of the
VTX detector covers \|z \|\< 11 cm. The combined reduction of these two
factors is gives about 28%. With 60% PHENIX uptime, which was achieved
in RUN3, the recorded luminosity is 17% of CA-D delivered luminosity.

The effective luminosity is further reduced by the fraction of "good
data" that can be used for offline analysis (the factor (a) ) and the
offline reconstruction efficiency (the factors (b) and (c)). Again,
these numbers are based on actual PHENIX performance and reconstruction
efficiency (tracking plus electron identification) for single electrons
in central arms in the RUN2 Au+Au data analysis. The reconstruction
efficiency includes the loss due to the dead channels in the central arm
detectors. The efficiency depends on the beam species, and it decreases
from *pp* to dAu to AuAu. This reduction is caused by occupancy
dependent efficiency losses, which are also based on the actual
performance in RUN2 data analysis. The reconstruction efficiency factors
are shown for both single electron (factor (b)) and electron pairs
(factor (c)).

We should emphasize that the reality factors given in Table 1 are all
based on achieved performance of RHIC and PHENIX and we assume no
improvement in the future. Therefore the effective luminosity presented
here is a very conservative estimate and potential improvements will
increase the effective luminosity usable by the VTX detector. In
particular, improvement in diamond size of the beam and the efficiency
of the storage RF would greatly increase the effective luminosity.

In Table 3 we list the delivered integrated luminosity, the recorded
integrated luminosity with the VTX (delivered integrated luminosity
times factor (4) in Table 2), and the effective integrated luminosity.
For the delivered integrated luminosity, we used the CA-D projection of
the RHIC luminosity in year 2008 RUN and assume constant effort, which
means 19 weeks of physics data taking per year. Since there is a very
large variation of the CA-D luminosity projection, we use the average of
the most pessimistic estimate and the most optimistic estimate. This
luminosity estimate is consistent with the five year extended beam use
proposal presented by PHENIX to the Physics Advisory Committee (PAC) in
the fall 2003. The most optimistic luminosity figure is about a factor
of 2 larger than shown in the table.

[]{#__RefHeading___Toc66641831 .anchor}Table 2 Table of efficiency
factors that must be applied to delivered pp, dAu and AuAu luminosities
to calculate expected signal yields. The single and two track
reconstruction efficiencies are for electrons in the central arm.

  ----------------------------- ------------ -------------- --------------
  Quantity                      p-p factor   D+Au factor    Au-Au factor

  \(1\) Storage RF efficiency   75 %         75 %           75 %

  \(2\) Event vertex cut (±10   38 %         38 %           38 %
  cm)                                                       

  \(3\) PHENIX uptime           60 %         60 %           60 %

  \(4\)                         17%          17%            17%
  L^recorded^/L^delivered^                                  
  =(1)×(2)×(3)                                              

  \(a\) Good run fraction       80 %         80 %           80 %

  (b)Single track efficiency    85 %         80 %           50 %

  \(c\) Two track efficiency    72 %         64 %           25 %

  Total (single                 12 %         11 %           6.8 %
  track)=(4)×(a)×(b)                                        

  Total (two track)=(4)×(a)×(c) 10 %         8.8 %          3.4 %
  ----------------------------- ------------ -------------- --------------

[]{#_Ref54638032 .anchor}

Table 3 Table of effective luminosities from a 19 week production run,
after reality factors are taken into account. The delivered luminosities
use the average of the most pessimistic and most optimistic C-AD
estimates of how the luminosity will evolve by 2008-2009. The signal
yield for a given process is found by multiplying the cross section for
the process by the effective luminosity and by the detector acceptance.
For d-Au and Au-Au collisions and the effective Ldt columns, the
nucleon-nucleon luminosities are shown in the parenthesis).

+-------+---------+---------+------------+------------+--------------+
| beam  | $$\     | de      | recorded   | Effective  |              |
|       | sqrt{s_ | livered | Ldt        | Ldt        |              |
| sp    | {\text{ | Ldt     |            |            |              |
| ecies | NN}}}$$ |         |            |            |              |
+-------+---------+---------+------------+------------+--------------+
|       |         |         |            | Single     | Double track |
|       |         |         |            | track      |              |
+-------+---------+---------+------------+------------+--------------+
| p-p   | 200     | 160/pb  | 27/pb      | 18/pb      | 15/pb        |
+-------+---------+---------+------------+------------+--------------+
| d-Au  | 200     | 40/nb   | 6.8/nb     | 4.4/nb     | 3.5/nb       |
|       |         |         |            | (1.7/pb)   | (1.4/pb)     |
+-------+---------+---------+------------+------------+--------------+
| Au-Au | 200     | 2.2/nb  | 370/b      | 150/ub     | 74/b         |
|       |         |         |            | (5.8/pb)   | (2.9/pb)     |
+-------+---------+---------+------------+------------+--------------+
| p-p   | 500     | 540/pb  | 93/pb      | 63/pb      | 54/pb        |
+-------+---------+---------+------------+------------+--------------+

In Table 4, the estimated signal yields of selected physics processes
are summarized. The "Yield" column of the table shows the raw signal
yield calculated as the product of the cross section, the geometrical
acceptance of the central arms, and the effective luminosity given in
Table 3. However, most of these raw signal yields cannot be measured or
cannot be separated from other competing process without the VTX
detector. The column "no VTX" indicates which of the physics signals can
be measured without the VTX detector (marked as "Yes") or not (marked as
"No"). If the signal can be measured with limitations or with a large
systematic uncertainty, the column is marked as "Limited". For example,
in charm decay electron measurement (*ce*), the first row (1\< *p*~T~
\<2 GeV/c) is marked as "Yes" since charm is the dominant source of
non-photonic electron in this *p*~T~ bin. The next row (2\< *p*~T~ \<3
GeV/c) is marked as "Limited" since there is a large uncertainty due to
the beauty contribution. All other rows are marked as "No" since it is
not possible to separate charm signal from the larger beauty signal for
*p*~T~\>3 GeV/c without the VTX detector. In these *p*~T~ bins, the
measurement of beauty decay electron (*be*) are marked as "Limited"
since we cannot separate *b* and *c* signal in a model independent way,
but the beauty contribution is larger than the charm contribution.

For the yield estimate of single electron from open charm (*ce*), the
momentum distribution of the charm decay electron is calculated using
PYTHIA event generator. The generator is tuned to re-produce the low
energy charm data from fixed target experiments and single electron data
at the ISR. The electron spectrum predicted by the tuned PYTHIA
simulation agrees well with PHENIX data at $\sqrt{s_{\text{NN}}}$=130
GeV and 200 GeV. The corresponding total charm cross at
$\sqrt{s_{\text{NN}}}$=200 GeV is 650 b per nucleon-nucleon collisions.
The single electron spectrum is then scaled assuming the binary scaling,
and then multiplied by the geometrical acceptance and the effective
luminosity to give the expected yield (sum of *e*^+^ and *e*^-^) shown
in the "Yield" column in the table. The expected yield in low *p*~T~
region (*p*~T~ ≤ 3 GeV/c) is consistent with the observed charm decay
electron yield in RUN2 Au+Au data. Since this estimate comes from a
scaled *p+p* PYTHIA simulation, it corresponds to a scenario with no
charm enhancement nor any energy loss. If there is a substantial energy
loss of charm in high *p*~T~, the actual yield of charm decay electron
could be smaller than the value in the table.

The yield of single electron from open beauty is estimated in a similar
way using PYTIA generator, assuming that total beauty cross section
is$\sigma_{b\overline{b}}$ = 3.8 b per N-N collisions. This cross
section is estimated by tuning the PYTHIA calculation of *b* production
with *b* production data from the Tevatron (1.8 TeV) and
$\text{Sp \{}\overline{p}S$collider (630 GeV) and then extrapolating
down to lower energies at RHIC (200 GeV). Binary scaling of the cross
section is assumed for the Au-Au estimates.

For both the charm and beauty decay electron measurements, the signal
yields with DCA \> 200 are shown in the column labeled "with DCA cut".
With the DCA cut, beauty is dominant over charm for *p*~T~ \>2 GeV/c,
and can be separated from the charm signal. In the lowest *p*~T~ bin
(1.0\<*p*~T~\<2.0 GeV/c), charm is still dominant over beauty by about
factor 5 with this DCA cut. The *b/c* ratio is improved to \~1/2 with
tighter DCA cuts (DCA\>400), as shown in the table, and *b/c* ratio
becomes about 1 with DCA\>800 (see Figure 18). Using the DCA
distribution, we can statistically separate the *b*-decay signal from
charm over the range 1\<*p*~T~\<6 GeV/c. The table shows that even with
the pessimistic assumptions used in the estimate, we will have
sufficient statistics for a *b/c* signal separation in this *p*~T~
range. Although the e/ separation power of the RICH detector is reduced
above its Cereknov threshold for pions (*p*~T~\>4.7 GeV/c), the
RICH+EMCAL combination has a sufficient *e*/ separation up to this
*p*~T~ range.

As discussed earlier, one of interesting measurement with the VTX is the
ratio of (*ce*)/(*be*) and its centrality dependence. Since most of the
systematic uncertainties cancelled in this ratio, the measurement is
primarily limited by the *b/c* separation from the DCA measurement and
the statistics of *be*. The expected yield of *b* and *c* signal with
and without the DCA cuts in Table 4 shows that we can reach \~1%
statistical precision in the ratio measurement.

A summary the physics program addressed with the VTX detector and how it
compares to the capabilities without the VTX is given in Table 5. For
many of these physics topics, a measurement is not possible without the
VTX detector or very marginal. For the processes that PHENIX can measure
without the VTX detector, the VTX will substantially extend the
kinematical range of the measurement. In addition, the accuracy and the
precision of the measurements are improved.

[]{#__RefHeading___Toc66641833 .anchor}Table 4 Event rate calculated for
selected physics processes. The effective integrated luminosity used in
the calculation is shown in Table 3. For the meaning of "no VTX" column,
see the text. In both of Au+Au and p+p, the collision energy
$\sqrt{s_{\text{NN}}}$ is 200 GeV per nucleon pair. The yields include
the anti-particle channels. The DCA cut value for the single electron
measurement is DCA\>200 . For the lowest pT bin, the number with
DCA\>400 is shown in parenthesis.

+--------------------------+-------+------------------+---------------+
| Process                  | no    | Yield            | Yield with    |
|                          | VTX   |                  | DCA cuts      |
+--------------------------+-------+------------------+---------------+
| AuAu*ce*                 |       |                  |               |
+--------------------------+-------+------------------+---------------+
| 1.0\<*p*~T~\<2.0 GeV/c   | Yes   | 3M               | 150K (40K)    |
+--------------------------+-------+------------------+---------------+
| 2.0\<*p*~T~\<3.0 GeV/c   | Li    | 130K             | 6K            |
|                          | mited |                  |               |
+--------------------------+-------+------------------+---------------+
| 3.0\<*p*~T~\<4.0 GeV/c   | No    | 5K               | 0.3K          |
+--------------------------+-------+------------------+---------------+
| 4.0\<*p*~T~\<5.0 GeV/c   | No    | 1K               | 50            |
+--------------------------+-------+------------------+---------------+
| 5.0\<*p*~T~\<6.0 GeV/c   | No    | 0.2K             | 10            |
+--------------------------+-------+------------------+---------------+
| AuAu*be*                 |       |                  |               |
+--------------------------+-------+------------------+---------------+
| 1.0\<*p*~T~\<2.0 GeV/c   | No    | 200K             | 50K (20K)     |
+--------------------------+-------+------------------+---------------+
| 2.0\<*p*~T~\<3.0 GeV/c   | No    | 70K              | 15K           |
+--------------------------+-------+------------------+---------------+
| 3.0\<*p*~T~\<4.0 GeV/c   | Li    | 17K              | 3K            |
|                          | mited |                  |               |
+--------------------------+-------+------------------+---------------+
| 4.0\<*p*~T~\<5.0 GeV/c   | Li    | 4K               | 0.7K          |
|                          | mited |                  |               |
+--------------------------+-------+------------------+---------------+
| 5.0\<*p*~T~\<6.0 GeV/c   | Li    | 1K               | 0.2K          |
|                          | mited |                  |               |
+--------------------------+-------+------------------+---------------+
| Au+Au*DK*                |       |                  |               |
+--------------------------+-------+------------------+---------------+
| *p*~T~ \>2 GeV/c         | No    | 4                | 1000          |
|                          |       | 900. (S/B\~0.1%) | (S/B\~3%)     |
| *p*~T~ \>3 GeV/c         | No    |                  |               |
|                          |       | > 2900 (S/B\~1%) | 600 (S/B      |
|                          |       |                  | \~5%)         |
+--------------------------+-------+------------------+---------------+
| Au+Au*BJ*/*ee*           | No    | 100              | 50            |
+--------------------------+-------+------------------+---------------+
| *ppce*                   |       |                  |               |
+--------------------------+-------+------------------+---------------+
| 1\<*p*~T~\<3 GeV/c       | Yes   | 10M              | 0.5M          |
+--------------------------+-------+------------------+---------------+
| *p*~T~\>3 GeV/c          | No    | 20 K             | 1K            |
+--------------------------+-------+------------------+---------------+
| *ppbe*                   |       |                  |               |
+--------------------------+-------+------------------+---------------+
| *p*~T~\>1 GeV/c          | No    | 0.9M             | 0.2M          |
+--------------------------+-------+------------------+---------------+
| *pp*+jet                 |       |                  |               |
+--------------------------+-------+------------------+---------------+
| 4\<*p*~T~\<5 GeV/c       | No    | 300K             | N.A.          |
+--------------------------+-------+------------------+---------------+
| 5\<*p*~T~\<6 GeV/c       | No    | 150K             | N.A.          |
+--------------------------+-------+------------------+---------------+
| 6\<*p*~T~\<7 GeV/c       | No    | 70K              | N.A.          |
+--------------------------+-------+------------------+---------------+
| 7\<*p*~T~\<8 GeV/c       | No    | 40K              | N.A.          |
+--------------------------+-------+------------------+---------------+
| 8\<*p*~T~\<9 GeV/c       | No    | 20K              | N.A.          |
+--------------------------+-------+------------------+---------------+
| 9\<*p*~T~\<10 GeV/c      | No    | 12K              | N.A.          |
+--------------------------+-------+------------------+---------------+
| *ppBJ*/*ee*              | No    | 560              | 280           |
+--------------------------+-------+------------------+---------------+

[]{#_Ref54757390 .anchor}

Table 5 Summary of physics measurement gained by the VTX detector. The
column "without VTX" shows the present capability of PHENIX, while the
measurement range with the VTX detector is shown in the column "with
VTX". If the process is not measurable, it is marked as "No".

+-----------------+-----------------+-----------------+-----------------+
| Process         | Physics         | Without VTX     | With VTX        |
|                 | Objectives      |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| *ce*            | Charm energy    | 0.5 \< *p*~T~   | 0.3 \< *p*~T~   |
|                 | loss            | \< 2.5 GeV/c    | \< 6 GeV/c      |
+-----------------+-----------------+-----------------+-----------------+
| *D* *K p*~T~\>2 | Charm energy    | No (2           | \> 7            |
| GeV/c)          | loss            | significance in | significance in |
|                 |                 | central Au+Au)  | central Au+Au   |
+-----------------+-----------------+-----------------+-----------------+
| Total charm     | Charm           | \~ 20 %         | \~ 10 %         |
| yield           | production      |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| (*ce*)/(*be*)   | Search for      | No              | \~ 1 %          |
| ratio           | thermal charm   |                 |                 |
|                 | produciton      |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| *be*            | Beauty          | *p*~T~\>3 GeV/c | 1 \< *p*~T~ \<  |
|                 | production      | with model      | 6 GeV/c         |
|                 |                 | dependence      |                 |
|                 | Beauty energy   |                 |                 |
|                 | loss            |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| *BJ*/           | Beauty          | No              | / \~ 10 - 15 %  |
|                 | production      |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| Total beauty    | Beauty          | No              | \~ 10 %         |
| yield           | production      |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| High *p*~T~     | Light quark     | *p*~T~ $$ 10    | *p*~T~ \< 15    |
| charged         | energy loss     | GeV/c           | -20 GeV/c       |
+-----------------+-----------------+-----------------+-----------------+
| *pp* *ce*       | *G(x)*          | 0.03 \< *x* \<  | 0.01 \< *x* \<  |
|                 |                 | 0.08            | 0.15            |
+-----------------+-----------------+-----------------+-----------------+
| *pp be*         | *G(x)*          | No              | 0.02\< *x* \<   |
|                 |                 |                 | 0.15            |
+-----------------+-----------------+-----------------+-----------------+
| *pp* +jets      | *G(x)*          | No              | 0.04\< *x* \<   |
|                 |                 |                 | 0.3             |
+-----------------+-----------------+-----------------+-----------------+
| *pA (dA)* *c/b* | Nuclear         | 0.03 \< *x* \<  | 0.01 \< *x* \<  |
|                 | shadowing of    | 0.3             | 0.3             |
|                 | G(x)            |                 |                 |
+-----------------+-----------------+-----------------+-----------------+

# 4. VTX Detector system

## 4.1 Overview

The VTX detector system is composed of 4 layers of silicon detectors, an
inner layer with silicon pixel hybrid detectors and three outer layers
with silicon strip detectors. A 3-D view of the detectors is shown in
Figure 24 and its cross sectional views are shown in Figure 10 in the
previous chapter. The geometrical dimensions are summarized in Table 6.

![](media/image31.png){width="4.4375in" height="4.4375in"}

[]{#__RefHeading___Toc66641795 .anchor}Figure 24 GEANT model of the VTX
detector. It consisted of the inner-most pixel layer and three outer
strip layers.

For the inner layer we will use silicon pixel detectors. The technology
is the ALICE1LHCb sensor-readout hybrid, which was developed at CERN for
the ALICE and LHCb experiment. The 200 m thick silicon sensor holds
32256×4 cells, or pixels, each with an active area of 50425 m^2^. The
sensor is bump bonded to four matching readout chips of 150 m thickness,
and each of the read-out chips has 32256 individual amplifier
discriminator channels. The readout chip also holds the electronics to
pipeline the data flow. We call a sensor bump-bonded to 4 readout chips
a sensor assembly. Two sensor assemblies are bonded on to a kapton
aluminum readout bus, which itself is supported by a carbon fiber
structure. The bus is connected to a unit called pilot module, which
provides all service voltages, control and timing signals, and reads out
the pixel data. The pilot module transmits the data via optical fiber
from the detector for further processing.

A unit of two sensor assemblies and one pilot module form a half ladder,
the basic building block of the detector. Two half ladders form a full
ladder and span approximately 22 cm in beam direction. Five such ladders
on each side of the beam pipe result in almost full azimuthal coverage.
A total of 10 ladders or 20 half ladders complete the inner layer. The
combined materials of silicon sensor, readout chip, readout bus and
mechanical structure including cooling add up to about 1.2% of a
radiation length.

The outer layers employ silicon strip sensors. The sensor, developed by
the BNL Instrumentation Division, allows stereoscopic readout on a
single sided sensor. Each sensor is about 3.436.46 cm^2^, with 2384
active strips of 80 m width and 3.1 cm length in beam direction
(x-projection) and a similar number of strips at an angle of 4.6^0^ to
the beam direction (u-projection). Due to the stereoscopic readout the
effective pixel size is 801000 m. Four sensors are mounted in a ladder
that subtends the full 25.8 cm longitudinal extent of the barrel. A
total of 42 ladders are required to cover the azimuth acceptance as
shown in Figure 24.

[]{#__RefHeading___Toc66641835 .anchor}Table 6 Summary of main
parameters of the 4 VTX layers.

+-------------+----------------+-----------+--------+-------+--------+
| VTX         | Layer          | R1        | R2     | R3    | R4     |
+-------------+----------------+-----------+--------+-------+--------+
| Geometrical | R (cm)         | 2.5       | 6      | 8     | 10     |
| dimensions  |                |           |        |       |        |
+-------------+----------------+-----------+--------+-------+--------+
|             | z (cm)         | 21.8      | 25.8   |       |        |
+-------------+----------------+-----------+--------+-------+--------+
|             | Area (cm^2^)   | 280       | 890    | 1240  | 1600   |
+-------------+----------------+-----------+--------+-------+--------+
| Channel     | Sensor size    | 1.28 1.36 | 3.43   |       |        |
| count       |                |           | 6.46   |       |        |
|             | R z (cm^2^)    |           |        |       |        |
+-------------+----------------+-----------+--------+-------+--------+
|             | Channel size   | 50 425    | 80 m 3 |       |        |
|             |                | m^2^      | cm     |       |        |
|             |                |           |        |       |        |
|             |                |           | (eff   |       |        |
|             |                |           | ective |       |        |
|             |                |           | 80     |       |        |
|             |                |           | 1000   |       |        |
|             |                |           | m^2^)  |       |        |
+-------------+----------------+-----------+--------+-------+--------+
|             | Sensors/ladder | 2 8       | 4      |       |        |
+-------------+----------------+-----------+--------+-------+--------+
|             | Ladders        | 10        | 10     | 14    | 18     |
+-------------+----------------+-----------+--------+-------+--------+
|             | Sensors        | 160       | 40     | 56    | 72     |
+-------------+----------------+-----------+--------+-------+--------+
|             | Readout chips  | 160       | 480    | 672   | 864    |
+-------------+----------------+-----------+--------+-------+--------+
|             | Readout        | 1,310,720 | 61,440 | 8     | 1      |
|             | channels       |           |        | 6,016 | 10,592 |
+-------------+----------------+-----------+--------+-------+--------+
| Radiation   | Sensor         | 0.2%      | 0.4%   |       |        |
| length      |                |           |        |       |        |
|             |                |           |        |       |        |
| (X/X0)      |                |           |        |       |        |
+-------------+----------------+-----------+--------+-------+--------+
|             | Readout        | 0.16%     | 0.7%   |       |        |
+-------------+----------------+-----------+--------+-------+--------+
|             | Bus            | 0.14%     |        |       |        |
+-------------+----------------+-----------+--------+-------+--------+
|             | Ladder &       | 0.7%      |        |       |        |
|             | cooling        |           |        |       |        |
+-------------+----------------+-----------+--------+-------+--------+
|             | Total          | 1.2%      | 1.8%   |       |        |
+-------------+----------------+-----------+--------+-------+--------+

Each strip sensor is wire-bonded to and read-out by twelve read-out SVX4
ASICs, six per orientation, and there are 128 channels on each SVX4
chip. Fermilab and LBNL have developed these chips for other silicon
vertex detectors. The twelve SVX4s servicing each sensor are mounted on
two beryllium oxide readout cards (ROC's). The six SVX4s per ROC are
readout by two identical, custom, digital ASICs, one per orientation.
These chips compress and parallelize the data sufficiently to meet
PHENIX readout speed requirements. Power, serial control, timing and
readout for a ladder are all carried on the ROC's, which are bussed
together via wire-bonding at their edges (one bus per orientation). This
bus runs the length of a ladder and out of the acceptance to a Pilot
Module, which transmits the data via an optical fiber for further
processing. The present estimate is that the mechanical support, ROC's
and sensor add up to about 1.8% of a radiation length.

Table 6 summarizes the main parameter of the VTX layers. The detector
system is discussed in more detail in the following sub sections.

## 4.2 Hybrid pixels

The inner layer of the vertex tracker will be build based on silicon
pixel devices designed for the ALICE experiment at CERN. The ALICE
collaboration has developed and is now constructing a silicon pixel
detector for its inner tracker. This detector system has to fulfill
similar requirements as the inner layer of the vertex detector proposed
for PHENIX. We therefore plan to develop and built the inner layer for
PHENIX in close collaboration with ALICE.

  ----------------------------------------------------- ----------------------------------------------------
  ![](media/image32.png){width="2.8027777777777776in"   ![](media/image33.png){width="2.857638888888889in"
  height="1.6277777777777778in"}                        height="1.0708333333333333in"}

  \(a\)                                                 \(b\)
  ----------------------------------------------------- ----------------------------------------------------

[]{#__RefHeading___Toc66641796 .anchor}Figure 25 (a) Cross section of a
pixel detector half ladder designed for the ALICE experiment. The hybrid
pixel detector itself consists of a readout chip that is connected via
solder bump-bonds to a sensor chip. Every sensor pixel has a
corresponding individual signal processing electronic in the readout
chip. They are interconnected with small solder balls ("bump-bonds") in
a flip-chip process. Eight pixel detector assemblies are wire-bonded to
a readout bus structure that runs along the detector on top of the
sensors. The half ladder is mounted onto a mechanical support with
includes embedded cooling lines to remove about one Watt of power
dissipated by the readout chip. (b) Arrangement of two sensor assemblies
with four chips each to form a PHENIX pixel detector half ladder. A bus
connects all readout chips. A pilot module outside of the acceptance of
the sensors interfaces the readout of the half-ladder to the data
acquisition system.

For PHENIX the pixel devices will be arranged in ladders, each ladder
carries 4 sensor assemblies, each with 4 readout chips bump-bonded to
one sensor chip. Two of these assemblies, comprising a half stave, are
wire-bonded to a Kapton-aluminum bus on which power, control and data
lines run. This is illustrated in Figure 25. A pilot module that is part
of the half stave but outside of the sensors\' geometrical acceptance
processes the incoming control signals and outgoing data of a half
stave. It carries an analog pilot chip for the power and reference
voltage supplies of the pixel readout chips, a digital pilot chip for
their controls and readout, and an optical link chip and transmitter for
the data transfer to the acquisition system.

### Sensor

The pixel detector sensors are designed in a planar technology of
CANBERRA and produced as p-in-n structures on 5" silicon wafers of 200 m
thickness. A pixel cell is defined by p^+^ implants in one side of the
n-type silicon. The pixel dimensions are 50 m by 425 m. Every sensor
pixel has a contact pad for bump-bonding to the matching electronics
pixel on the readout chip.

The array of 32 by 256 pixels is read-out by a single readout chip. The
array is surrounded by a guard ring electrode that protects the
detection area from leakage currents deteriorating the signals generated
by charged particles in the depleted silicon. The guard ring also
encircles a "snake" structure for quality tests of the bump bonding
during the mass production of the assemblies. Those "snakes" have
matching structures and contact pads for probing access on the readout
chip. A scribe line defines the outer dimensions of the device for the
wafer dicing and also contains alignment marks. Figure 26 shows a
photograph of a corner of such sensor.

A sensor chip as produced for ALICE pixel detector prototypes and the
NA60 pixel vertex spectrometer is of 12.8 by 13.6 mm^2^ size and has
array of 32 by 256 pixels. On a PHENIX pixel sensor chip, four such
sensor pixel arrays are implemented in a linear arrangement on a single
substrate[^28]. The long side of the pixels is parallel to the long
direction of the chip. The 200 m thick sensors deplete typically at 12V
applied to the aluminized n^+^ implanted continuous back plane. During
operation in the experiment, the sensors are over-biased. The leakage
currents are as low as a few nA in well diced material but can go up to
a few A without any danger to the sensors' functionality.

Several sensor chips are arranged on the production mask of a 5" wafer.
Dedicated p-in-n diodes between the sensor chips are production-specific
to the CANBERRA technology and serve the quality survey in the foundry.

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[]{#__RefHeading___Toc66641797 .anchor}Figure 26 Photograph of a corner
of a pixel detector sensor chip, seen through a microscope. A guard
electrode surrounds the array of pixel implants. The scribe line defines
the outer dimensions of the die.

### Readout chip

The pixel detector front-end electronics ("readout chip") results from a
research and development effort at CERN that started more than a decade
ago[^29]. The recent chip "ALICE1LHCb" is a mixed analog-digital ASIC
designed in CERN\'s EP-MIC group and the ALICE and LHCb teams for an
application in the Silicon Pixel Detector of the ALICE experiment and
the RICH photo detection of the LHCb experiment at the LHC[^30]. It is
also being applied in the vertex spectrometer of the NA60 experiment at
the SPS[^31]. The chip is designed in a 0.25 m process with radiation
tolerant design layout techniques. Each chip has 32 by 256 pixels of 50
m by 425 m size. It is designed to be bump-bonded with solder balls of
about 20 m diameter to a silicon sensor that contains an array of sensor
pixels with matching size and pitch. The chip provides a binary output
signal for every pixel that indicates a charge release by a traversing
particle. The threshold of the pixels\' discriminators and various other
parameters of the front-end electronics can be adjusted and programmed
individually for every pixel. An analog pilot chip provides the
reference levels for the readout chip. Typical thresholds for particle
detection are below 2000 e^-^, while the electronic noise is below 200
e^-^ equivalent noise charge. For single pixel hits the mean sensor
signal from minimum ionizing particles in 200 m Si is about 16000 e^-^
so that a superb signal-to-noise ration is achieved. Each ALICE1LHCb
chip is readout by clocking out 256 32-bit words at a frequency of 10
MHz.

### Interconnection of Sensor and Readout Chip ("Bump Bonding")

The term "bump-bonding" denotes the micro-interconnection of electrical
structures with small "balls" of metals or alloys. It is essential for
the construction of modern hybrid structures with two-dimensional arrays
of high-density designs. Bump-bonding and flip-chip interconnection
techniques were already introduced in the late 1960s. They became
commercially available only about 15 years ago. Bonding with dimensions
smaller than approximately 50 m is still offered by only a rather small
number of vendors or specialized laboratories, and becomes challenging
at below 20 m for specialized applications.

The Technical Research Centre of Finland (VTT), Microelectronics
Department of the Information Technology Division, is the vendor of
choice at CERN for the production of flip-chip assembled pixel detectors
for the ALICE and LHCb experiments. VTT offers an integrated package of
bump-bond deposition, wafer thinning and flip-chip bonding[^32]. Key
features of the process are:

-   200-mm (8\'\') wafer capability.

```{=html}
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```
-   Tin-lead solder alloy bumps are used for mechanical strength of the
    bonded assemblies.

-   Bump deposition by electroplating.

-   Optional thinning (back grinding) of bumped readout wafers from
    native thickness of 750 m down to 150 m.

-   Clean dicing with front side protection using either photo resist or
    tape.

-   Flux less flip chip bonding. Alignment accuracy better than m

-   Bump size down to smaller than m diameter.

-   Throughput 3-4 assembly bondings per hour.

Statistics from the recently finished production of bump-bonded
assemblies for the NA60 pixel vertex spectrometer, with chips of 750 m
and sensors of 300 m thickness, illustrates that the industrial process
of VTT is able to produce good yield for 20 m bump bonds.

In 2003, a grand total of 132 single-chip pixel detector assemblies were
produced in multiple batches for NA60 at VTT. Out of those, 115
assemblies passed the acceptance test, i.e. had less than 1 % dead or
noisy pixels. An example is shown in Figure 27. The average yield of
accepted assemblies was 87 %. Several large batches, especially towards
the end of the production, had a significantly higher yield than this
average and reached even 100 % of accepted assemblies. In the same
process, first pixel sensor assemblies were successfully produced for
the ALICE experiment. Each of the assemblies contains five readout chips
placed on a silicon sensor substrate of about 14 mm by 70 mm size that
has five matching sensor pixel arrays implemented. The processing
included the thinning of the readout chips to 150 m before they were
bump-bonded to the sensor.

  ---------------------------------------------------- ----------------------- -----------------------
  ![](media/image35.png){width="5.999305555555556in"                           
  height="1.8305555555555555in"}                                               

  \(a\)                                                \(b\)                   \(c\)
  ---------------------------------------------------- ----------------------- -----------------------

[]{#__RefHeading___Toc66641798 .anchor}Figure 27 Test result of a
typical high-quality ALICE1LHCb assembly for the NA60 experiment: (a)
Test pulse injection into readout chip: 8 out of 8192 pixels are dead,
the rest of the pixel array responds. (b) Source measurement with Sr^90^
to test the bump bonding quality: 3 out of 8192 bonds are open (or
pixels do not respond electrically). (c) Image of a beta source with
shadow of the depletion voltage contact needle on the silicon sensor.

The requirement for thinnest possible detectors especially in the
internal layers of the vertex detector, to minimize multiple scattering
and photon conversion, demands the thinning of the readout chips. The
native thickness of electronics wafers is 750 m when they leave the
foundry. Since they are processed only from one side, in a layer of only
a few micron depths, a large fraction of the bulk can be removed without
affecting the electrical properties of the chip. Sensor wafers are
processed from both sides to establish the p-in-n structures, and have
to be directly produced in their final thickness. At VTT, a procedure
has been developed to thin readout chips in a way that conforms to the
mechanical stability requirements for bump-bonding and flip-chip
assembly. After the electrolytic deposition of solder bumps on a full
readout wafer, and before the flip-chip process is performed, the
wafer\'s surface is first protected with a removable film. The backside
is then grinded mechanically in several steps. Finally, wet chemical
etching or chemical mechanical polishing removes the defect layer. The
minimum thickness achieved with 8\'\' wafers is 150 m, with thickness
variations of less than 5 m.

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[]{#__RefHeading___Toc66641799 .anchor}Figure 28 Map of working pixels
from a source measurement of a thin ALICE pixel sensor assembly. The
sensor assembly consists of five thinned readout chips of 150 m
thickness that are bump-bonded to a 200 m thick silicon sensor
substrate. The fraction of working pixels is indicated for every chip

A small number of thin sensor assemblies have been produced so far for
the ALICE experiment, prior to the start of the mass production. The
test production yielded several well working sensor assemblies. Figure
28 illustrates a test result from one thinned sensor assembly with five
readout chips[^33].

### Readout Bus

The Pixel bus is a printed circuit sandwich made from Kapton and
aluminum/copper layers to provide power and control signal for the pixel
readout chips, and to bring signals out to Pixel pilot module. The
connections between readout chip and pixel bus are made by wire-bonding.
The metal layers are arranged in vertical steps along the long side of
the bus in order to be able to wire-bond the readout chips to the bus.
The dimension of the pixel bus will be about 40 cm long, where pixel
pilot modules are placed and 1.4 cm wide which is same as the width of
pixel readout chip. In the current design, the pixel bus is composed of
five metal layers: ground, power, signal lines and a layer for detector
bias and auxiliar passive components. The cross section of the pixel bus
is seen in Figure 29.

![](media/image37.png){width="6.03125in" height="2.129861111111111in"}

[]{#__RefHeading___Toc66641800 .anchor}Figure 29 Cross section of the
structure of the pixel bus. Two technical solutions are being
investigated. Option (a) contains a high-density double-layer of signal
lines, with a mean line pitch of 70 µm.\
Option (b) uses a reduced line-density on two signal double-layers with
an average line pitch of 140 µm.

"Horizontal lines" on one component of the signal double-layer are
running parallel with the long direction of the pixel bus to rout the
signals to the Pilot module. "Vertical lines" on the other component are
connect to bond pads on the side of the bus for the wire-bonding to the
readout chips. Through-hole connections between the horizontal and
vertical lines to interconnect the two signal layer components. Since
four ALICE1 chips must be read out in parallel to meet PHENIX timing
requirement, 190 signal and control lines are needed in the horizontal
layer, which corresponds to 70 m line pitch in a single signal layer as
seen in Figure 29(a). The capabilities of industrial partners are being
explored for a production of such fine pitch aluminum lines. However,
technology to make lines with 60 m pitch in a copper layer is
commercially available. For this reason, a five-layer pixel bus with
copper lines for the horizontal and vertical layers, and other lines
made from aluminum will be our back-up solution. The material budget for
the back-up option will be 0.236 % radiation length. To make a further
reduction of the material budget possible, the effort to produce a pixel
bus with exclusively aluminum lines will be continued. Due to the
technical difficulty with producing 70 m pitch aluminum lines, the
addition of another signal layer in the pixel bus will be an option. The
cross section of the pixel bus made exclusively from aluminum metal
layers is seen in Figure 29(b). For this option, the signal line pitch
will be 140 m and the thickness for the pixel bus will be 0.139 %
radiation length.

### Pilot module

The pilot multi-chip module carries three chips that support the readout
and control of the pixel readout chips of every half-ladder: An analog
and a digital pilot chip, and a link driver chip with optical
transceiver. The components are arranged on a multi-layer printed
circuit with copper lines and interconnections.

The key component on the Pilot module is the digital pilot chip. The
role of the digital pilot is to read the data from the ALICE1LHCb chip.
Upon pixel chip readout being initialized, each ALICE1LHCb presents 256
sequential words of pixel data on a 32-bit bus synchronously at a 10MHz
clock. Thus, 25.6μs is required to read the data from a single chip. In
the PHENIX data acquisition system, the readout is ultimately performed
in 40μs to achieve a maximum throughput of 25 kHz. A sequential readout
of the 8 chips on two half ladders requires 204μs to empty the pixel
chip data into the pilot, and hence does not meet our timing
constraints. To satisfy the readout time requirement of PHENIX, we must
readout for pixel chips in parallel, thus 432-bit data will be
transmitted to the Pilot module. We are currently investigating several
options of the Pilot module design to handle four times more data bits
than the ALICE Silicon Pixel Detector (SPD) has.

One solution could be to read out each of the parallel branches with one
of the existing ALICE pilot ASICs. Since in the PHENIX vertex detector
environment free space is available between the end-cap detectors and
the magnet poles ("nose cones"), unlike in the extremely tight ALICE
Inner Tracker region, such a solution with multiple ALICE pilot chips
can be considered. It would require about four times the space of an
ALICE pixel pilot module (external dimensions: \~80 mm by 13.8 mm), and
also four times more optical fiber lines to read or control data from
the half ladder. For the ALICE design, three fibers (clock, control,
data link) are connecting to the Pilot module.

The other solution is based on a new pilot chip. It may be implemented
either as a new version of the ALICE pilot ASIC or a rad-hard FPGA
adapted to PHENIX. These two options are being investigated in
collaboration with the ALICE SPD group. The ASIC option uses the same
design rules and radiation tolerant technology as the Pilot ASIC that is
presently already functional. A first version of the modified digital
pilot chip which handles 232 bit data inputs will be submitted as part
of a multi project wafer at CERN to IBM in May 2004. This option
requires only twice the space than the present design of the ALICE pixel
pilot module, and twice the number of optical fibers. The same PILOT
design can be implemented in a rad-hard FGPA with potential advantages
in schedule, costs and the flexibility to provide extra functionality,
e.g., zero-suppression.

### Front End Modules 

The pilot module transmits its data via optical fiber. A front-end
module (FEM) will communicate with the pilot module on one side, and the
PHENIX DAQ and slow control system on the other side. Since the pilot
module transmits the data via optical fiber, the FEM can be located in
electronic racks away from the vertex region. Each FEM may receive data
from several pixel half ladders and thus reduce the number of Data
Collection Modules (DCM) needed to interface to the PHENIX DAQ. In order
to allow simple manipulations of the data, the FEM will pipe the data
through an FPGA. This FPGA will add data headers and trails to for
standard PHENIX data packages. Optionally the data may be further zero
suppressed at the bit-level at this stage to reduce the data volume that
need to be transferred. The design of the FEM is very similar to FEM\'s
that are currently employed in the PHENIX readout system.

We are investigating to what extent the FEM\'s may also be used to
extract information from the vertex tracker for the second level
trigger. The basic idea is to let the FPGA group the data into super
pixels, which provide rough hit information. The hit information from
all FEM\'s could then be transmitted to a local trigger processor to
calculate trigger primitives in real time. The hit information could be
correlated with other information, like electron identification in the
PHENIX RICH and EMCal, by more elaborate algorithms, while the event is
analyzed by the PHENIX second level trigger processors farm. In
principle, if the data of the silicon strip detectors is also passed
through similar modules at the same location the information of all
layers of the vertex detector could be correlated and a rough secondary
vertex tracking may be feasible.

[Assembly of pixel detector ladders and the barrel detector
layer:]{.underline}

The assembly of the pixel detector modules will be performed in a
two-step procedure that yields half-ladders and is outlined here. All
components that go into the assembly (sensor ladders, pixel bus, pilot
module, power cable) have passed specific quality acceptance tests.

In the first step, the two sensor ladders are geometrically aligned on
an assembly fixture, with the sensors facing up. Glue is deposited on
the sensors. The pixel readout bus is then aligned with respect to the
sensor ladders and brought into contact with the glue. It is important
that especially the area under the bond pads of the pixel bus is
properly glued, in order to yield mechanical stability for the
wire-bonding. The glue must be electrically insulating and elastic
enough to reduce mechanical stress that occurs with temperature cycling
during the operation of the pixel detector. Due to the fragility of the
sensor ladders, no pressure can be applied during the gluing process.
The curing temperature must be low enough to exclude damage to the
solder bump bonds. A power cable, and the pilot module in about 40 cm
distance at the other end of the pixel bus, can be glued in a similar
way, with the corresponding contact pads of the components aligned.

In the second step, the interconnections between readout chips and pixel
bus are established by wire-bonding. Also the sensor bias connection
using dedicated wire-bonding pads as well as the interconnections
between pixel bus and pilot module are established.

Finally, the fully assembled and tested pixel detector half-ladders are
mounted onto the VTX barrel support with a tool that lifts the
half-ladders from their assembly fixtures and places them in their final
positions. On the barrel support, thin aluminum grounding foils are
already installed, which establish a well-defined electrical potential
to the back side (bulk) of the pixel readout chips. The glue between
pixel chips and grounding foil is therefore required to be electrically
conductive. It must also provide good thermal conductivity for the heat
transfer to the cooling system that is embedded in the mechanical
support. Since no mechanical pressure can be applied, a candidate
technology is a glue that hardens quickly under exposure with UV light
that is emitted from a light guiding tool at the side of the ladder once
the final contact between ladder and support has been established. An
electrically insulating glue with good thermal conductivity and adhesion
to the support material is required between the grounding foil and the
barrel support.

### Pixel detectors operating in the NA60 experiment:

Hybrid pixel detectors as described above are already being applied in
the NA60 experiment at the SPS at CERN. NA60 studies the production of
open charm and prompt dimuons in collisions induced by proton and heavy
ion beams on nuclear targets. For this task, several novel detector
systems were added to the dimuon spectrometer and zero-degree
calorimeter, which were previously used in the NA50 experiment. The main
upgrade is a new silicon pixel vertex spectrometer, which contains a
tracking telescope, shown in Figure 30 that is built from ALICE1LHCb
pixel detectors. Ninety-six single-chip pixel assemblies are arranged on
16 tracking planes with 4 or 8 chips that are operated on pixel busses
on ceramic substrates. The readout electronics utilizes the pilot
prototype chip that was developed for the ALICE Pixel Detector, and the
driver chip developed at CERN for the optical link.

In the year 2002, during the construction phase of the NA60 pixel
detector modules, a sub-set of three tracking planes was operated in the
experiment and used to track particles in low-energy Pb-Pb collisions.
The run confirmed the feasibility of the detector concept in both
technical aspects of the module construction and the vertex
reconstruction performance[^34]. One half of the telescope was then
characterized in a test beam run in September 2003. The full telescope
with 16 detector planes was installed and operational in the NA60
experiment during the physics run with high-energy Indium beams in Fall
2003 (Figure 31). The full readout chain has been working well in the
NA60 data acquisition system.

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[]{#__RefHeading___Toc66641801 .anchor}Figure 30 The vertex spectrometer
of the NA60 experiment comprises a 16-plane pixel detector telescope
mounted in a 2.5 T dipole magnetic field in 7 cm to 32 cm distance
downstream of the targets. Every plane is built from four or eight
ALICE1LHCb single-chip pixel detector assemblies, which are mounted on
ceramic printed circuit boards

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[]{#__RefHeading___Toc66641802 .anchor}Figure 31 Average-multiplicity
event in collisions of a 158\~AGeV/c Indium beam with a segmented Indium
target, reconstructed with 16 pixel detector planes during the physics
run of NA60 in Fall 2003.

## 4.3 Silicon Strip Detector

We plan to instrument the outer three layers of the VTX with silicon
strip detectors of a novel design. The sensors developed by the BNL
Instrumentation Division provide two-dimensional position sensitivity
with single-sided processing. A first set of prototypes has been
produced and tested using the VA2 readout chip, which was not well
matched to the sensor. The next generation of prototypes is under
development. They will be readout by SVX4 chips, which were developed
for silicon strip detectors by FNAL and LBL. If the test results are
satisfactory the SVX4 will be our choice for the readout of the sensors.
In the final readout system the SVX4 chips would be arranged on readout
cards (ROC's) and mounted directly on the sensors. The ROC's would also
provide the data bus, power distribution, and all necessary control
signals.

### Strip Sensors

Principle Design

The sensor is a finely grained detector with 80m1000m pixels. Each pixel
region has two serpentine-shaped metal strips (Figure 32) that collect
charge that diffuses after an ionizing particle transverses the silicon.
Any one hit will deposit charge on two serpentines. A metal strip
connects those serpentines that are in a straight line (X-direction),
while a second strip connects serpentines that are at a 4.6 degree angle
(U-direction). This provides a stereoscopic X-U readout and thus
two-dimensional information from one side of the sensor.

![](media/image41.jpeg){width="5.992361111111111in"
height="2.7576388888888888in"}

[]{#__RefHeading___Toc66641803 .anchor}Figure 32 A schematic view of p+
cathode structure of the pixels.

Figure 33 shows a schematic view of the prototype strip sensors and
their geometrical dimensions. The total size of the sensor is
34.3mm64.6mm. Each sensor is divided into two sides of separate
sensitive areas with a dimension of 30.7mm×30.0mm. The active areas are
segmented into pixels of 80m1000m, which are connected to X- and
U-strips as discussed above. Each strip sensor has a total of 1536
channels, 2384 channels per side, half of them in X- and the other half
in U-direction. First prototypes where produced with 250 and 400 m
thickness. These detectors have been tested in the laboratory and in
beam. The next generation of prototypes is being developed and we expect
to test their performance in the first half of 2004.

![](media/image42.png){width="5.956944444444445in"
height="4.958333333333333in"}

[]{#__RefHeading___Toc66641804 .anchor}Figure 33 A schematic view of the
prototype silicon strip sensor.

### Laboratory tests of the strip sensors 

The initial tests of the prototype sensors have shown good results.
Figure 34 shows the measured current and capacity as a function of the
bias voltage. Full depletion is achieved at a bias voltage of \~80 V. At
this voltage the capacitance of each strip is \~10 pF and the leakage
current is less than 10 nA.

To test the sensors in more detail, the Instrumentation Division in BNL
has constructed a laser test setup. During the R&D phase the laser setup
allows to studies of the properties of the sensors and to find the
optimum operation condition, which includes the depletion voltage, the
charge collection efficiency, the response to the carrier drift process,
electric field profile inside the sensor and so on. The transient
current technique (TCT)[^35] \[1\] is applied to obtain the electrical
properties of the sensors. The technique is based on the analysis of the
current and/or charge pulse shapes, which arise from electron-hole pairs
created inside the detector by injecting the fast laser light. During
the mass production of sensors, the existing setup or a newly developed
setup based on our experience will provide the basic tool for quality
control of the strip sensors and later of the assembled detector
ladders.

![](media/image43.wmf){width="3.12992125984252in"
height="2.5515748031496064in"}![](media/image44.wmf){width="2.765354330708661in"
height="2.351574803149606in"}

[]{#_Ref54530969 .anchor}

Figure 34 Current and capacity characteristics of a prototype sensor.

shows the schematic layout of the laser test setup. The picture of the
laser test setup is shown in Figure 36. A nano-second pulsed laser
coupled into a focuser through an optical fiber is operated with a pulse
generator. Two types of laser are used in the laser tests. One is a red
laser with the wavelength of 635 nm and the penetration depth of 3 μm in
silicon, and the other is an infrared laser with the wavelength of 1060
nm and the penetration depth of 800 μm in silicon. The red laser is used
to study the separate collection of electrons and holes. The infrared
laser is used to study the response of the detector to the charge
deposition of a minimum ionizing particle (MIP). The focuser was fixed
to a XYZ motorized stage. The precision of the laser spot positioning
with the motorized stage is 0.5 μm. The laser spot size achieved after
focusing is about 10μm in diameter. The current laser test setup is
controlled with manual controllers and will be upgraded to have an
automatic control with a LabVIEW compatible multi-axis motor drive.

![](media/image45.png){width="4.639583333333333in"
height="2.7756944444444445in"}

[]{#__RefHeading___Toc66641806 .anchor}Figure 35 Schematic layout of the
laser test setup.

![](media/image46.jpeg){width="4.444444444444445in"
height="3.3465277777777778in"}

[]{#_Ref54530872 .anchor}

Figure 36 The laser test setup for the strip sensor.

### Sensor Prototypes in Test Beam

To test the prototypes in beam, the sensors were mounted on readout
cards designed to read out signals from one side of the sensors (Figure
37). Each plane consists of a silicon strip sensor, six readout chips, a
base-board, two fan out boards (pitch adaptors) and two SMT boards. A
bias voltage was applied in the sensor backplane (ohmic side) through
the base-board. An analog multiplexer readout chip with 128-channel
charge sensitive preamplifier-shaper circuits, VA2 chip of Ideas
ASA[^36], was used to read out signals from the sensor. The
preamplifier-shaper has a 1-3 μsec peaking time and a nominal gain of 30
mV/pC. The SMT board was designed to operate the VA2 chips and read out
multiplexed analog signals through an interface with a VME data
acquisition system. Three detectors planes with 400 μm thick sensors and
four with 250 μm thick sensors were constructed.

![](media/image47.png){width="3.561111111111111in"
height="2.676388888888889in"}

[]{#_Ref54543695 .anchor}

Figure 37 The prototype detector

The sensor performance in terms of charge sharing properties, detection
efficiency and position resolution has been evaluated with a ^90^Sr
β-source and in the test beam at KEK. The beam test was performed at T1
beam line in KEK-PS, which delivered a positively charged particle beam
with momentum of 0.5 - 2.0 GeV/*c*.

Charge sharing property in x-strip and u-strip can be characterized by
the asymmetry, A~Q~ = ( Q~x~ - Q~u~ ) / ( Q~x~ + Q~u~ ), where Q~x~ and
Q~u~ represent collected charges in x-strip and in u-strip,
respectively. For an optimum two-dimensional position sensitivity, one
expects that A~Q~ on average is zero with a narrow width. The results of
the A~Q~ measurements are plotted in Figure 38. The source test shows
the A~Q~ distribution peaking at zero with a width of about 0.18. This
demonstrates that the principle of two-dimensional position sensitivity
by charge sharing works. In the beam tests A~Q~ exhibited a dependence
on the incident angle of the beam normal to the sensor surface, θ~inc~.
For θ~inc~ = 15 degrees and 30 degrees narrow distribution with a peak
at zero were observed. However, at θ~inc~ = 0 degrees broad
distributions which did not peak at zero were found. This deficiency was
traced back to the line width (8m) and gap spacing (5m) of the p+
electrode structure in a single pixel. For the second-generation
prototype sensors a narrower line width (5m) and gap spacing (3m) was
chosen to overcome this problem.

![](media/image48.png){width="6.0in" height="1.6888888888888889in"}

![](media/image49.png){width="6.0in" height="1.8486111111111112in"}

[]{#__RefHeading___Toc66641809 .anchor}Figure 38 Charge correlations in
between x-strips and u-strips found in tests with a radioactive source
and with beams of charged particles.

The position resolution was measured from the residuals of hits on
reconstructed particle trajectories. As is shown in Figure 39 the rms
width of the residual distribution for a single strip is about 40 m.
After de-convoluting the fit bias and the contribution of multiple
scattering, the intrinsic position resolution of the detector is 23 - 25
m. This is consistent with the expected resolution for a strip detector
of 80 m pitch (80/$\sqrt{\text{12}}$=23.1).

![](media/image50.jpeg){width="6.0in" height="2.272222222222222in"}

[]{#__RefHeading___Toc66641810 .anchor}Figure 39 Hit residuals from
tracks found using the silicon strip sensors in a test beam experiment.

In this beam test, a reliable measurement of the efficiency of the
sensors was not possible. In part this is due to the imperfections in
the charge sharing, but more prominently the readout chain suffered from
a severe common mode noise, which lead to a small signal-to-noise ratio
and prohibited an efficient hit detection. At present only the lower
limits for the efficiency can be quoted, they are 98%, 96%, and 88% for
three 400 μm thick sensors and about 60% for two 250 μm sensor. The
detection efficiencies and the signal-to-noise ratios are under study
and are expected to be improved by optimizing the operational condition
of the detector and by introducing a more appropriate readout chain
based on the SVX4 chip.

### The Second Prototype Sensor and Tests with SVX4 Readout Chip

The second prototype sensor was designed to have 5 μm line width and 3
μm gap spacing of the p^+^ electrode structure in a single pixel. The
sensor is expected to have better charge-sharing property, compared with
the first prototype sensor with 8 μm line width and 5 μm gap spacing.
The second prototype sensor has been processed by the BNL
Instrumentation Division. Four sensors with 400 μm thickness were
fabricated in the end of January, 2004. Four sensors with 500 μm
thickness will be fabricated by the end of March, 2004.

The detector composed of the second prototype sensor and the electronics
hybrid with the SVX4 readout chips is under preparation. The study of
the signal-to-noise ratio in the detector is essential for the strip
detector development. The design of the detector is similar to the first
prototype detector shown in Figure 36. The VA2 chips and the SMT board
in the first prototype detector are replaced to the electronics hybrid
shown in Figure 40, which is developed for CDF Run2b Silicon Detector.
Three of four SVX4 chips mounted in the hybrid are used to readout 384
X- or U-strips of the sensor. One hybrid received from the CDF
collaboration is used for the detector. The hybrid is operated by using
a test board described below, which is a simplified version of the
PHENIX DAQ.

The SVX4 chip is designed for the usage of an AC-coupling strip sensor.
Possible problems in the detecor of the DC-coupling sensor and the SVX4
chip are the saturation of the preamplifier by the integrated leakage
current and the noise due to the fluctuation of the leakage current. We
plan to study the signal-to-noise ratio by DC-coupling between the
sensor and the SVX4 chip at the first stage. We expect that the
preamplifier saturation is solved by resetting the preamplifier during
the period corresponding to the RHIC beam abort gap and the noise
fluctuation is overcome by the Real-Time Pedestal Subtraction (RTPS)
feature implemented in the SVX4 chip, which allows us to subtract the
average pedestal event-by-event.

We will also study the signal-to-noise ratio by AC-coupling between the
sensor and the SVX4 chip if DC-coupling between the sensor and the SVX4
is found problematic. The study can be made by inserting SMD capacitors
and resisters between the sensor and the SVX4 chip. This AC-coupling
scheme solves the matching issue of the sensor and the SVX4 chip in
principle. Once the specification of the SMD components is fixed, we can
transfer the specification to a small chip with capacitors and resisters
called "RC chip", which Hamamatsu has experiences to make.

### SVX4 readout chip

The strips will be read out with the SVX4 chip developed by
Fermilab/Berkeley collaboration. The SVX4 is implemented in the 0.25 m
TSMC process and is inherently rad-hard. It is a 128-channel chip with a
46-deep pipeline cycled by the beam-crossing clock, thus providing the
LVL1-latency required by the PHENIX DAQ. LVL1-accepted events are stored
for future pipelined readout. The SVX4 allows up to 8 bits of analog
information, although the number of bits are programmable. Several
pedestal-subtraction steps offer robust protection against common-mode
noise. On-board zero suppression is provided for, but can be turned off
(see discussion below). The SVX4 also provides for four-deep multi-event
buffering required by the PHENIX DAQ. Fermilab has a complete
wafer-testing station and has indicated a willingness to take on the
required wafer testing of our chips. A test board has been developed at
ORNL that has allowed us to verify compatibility of the SVX4 with the
PHENIX DAQ (serial programming, clock & fast control and data read-out).
Integrated SVX4/sensor tests will begin next month.

In fall 2003 FNAL cancelled the Tevatron Run-II silicon upgrade
projects. There are already sufficient SVX4 chips that have been
produced to meet our needs. We are in negotiations with FNAL for the
purchase of these chips. In the present plan, we will purchase 18 wafers
of the SVX4 chip, which should produce about 5,000 good chips based on
the measured good chip yield. This is more than twice of what we need
(2016 good chips plus spares).

### Sensor Readout Card (ROC) / Readout Bus

CDF has implemented readout of a silicon detector using 2cm x 4cm BeO
circuit boards holding four SVX4 chips operating in a daisy-chain mode
to reduce signal bus requirements, see Figure 40. We have chosen a
similar implementation, but we require six SVX4 chips in a 3cm x 3cm
area to readout both orientations (768 channels) of half of a sensor.
Using a nomenclature common to a number of other PHENIX subsystems the
circuit boards hosting the SVX4s are termed Readout Cards (ROC's). There
are 2 ROC's per sensor, 4 sensors per ladder and 42 ladders for a total
of 336 ROC's (and 2016 SVX4s).

In addition to six SVX4s, each ROC has one custom, digital ASIC (or
perhaps a rad-hard FPGA), known as the ROC Control Chip (RCC). The
technology choice between an ASIC or a rad-hard FPGA will be made based
on radiation dose measurements and space constraints. Since these chips
are purely digital they can be completely tested inside an FPGA
implementation (greatly simplifying any necessary revisions) and a
technology choice can be postponed.

The RCCs are relatively simple, with a block diagram shown in Figure 41,
below. They effectively serve as a state-driven de-multiplexer,
directing the serial and clock & fast control inputs and the data
outputs, depending on the SVX4 state selected (*Initialize*, *Digitize*
or *Readout*) and on the geographical address of the ROC. They also hold
digitized data awaiting readout (the SVX4 itself buffers four
un-digitized events tagged with a Level-1 accept signal). The simplicity
of this chip has two important consequences: 1) The chip's size will
likely be determined by the required number of I/O pins (\~ 50 signals,
primarily differential LVDS), with 5mm^2^ likely to be sufficient. 2) If
expected dose or space limitations require the use of an ASIC we expect
it to be relatively straightforward to convert from the FPGA
implementation to an ASIC, although the layout of an ASIC version would
need to take the radiation environment into account.

The SVX4 cannot read out one event and digitize another at the same
time. But, in order to conform to the PHENIX DAQ requirements, the
system must be prepared to be read out a second event immediately after
a prior event is read out. The RCC is therefore required as a buffer to
hold data read out from the SVX4s immediately after digitization so that
they will be prepared to read out a second event by the time the entire
ladder is read out. Furthermore, it also serves to minimize the effects
of single-point failures (one broken SVX4 could take out all of the
chips in its serial path).

The connection of the SVX4 to the sensor may be complicated by two
factors: 1) the SVX4 is designed to be AC coupled, but the strip-pixel
sensor is DC coupled, 2) the input pitch of the SVX4 is 48 m and the
strip pitch is 80 m.

There are two consequences of the difference in coupling. The first is
that the leakage current from the sensor will rapidly saturate the SVX4
input preamp. The preamp dynamic range is 200 fC, which will saturate in
20 sec. However, we can issue a preamp-reset signal once per RHIC abort
gap (\~13 sec) allowing a hit rate per strip-pixel of \~2MHz before
saturating between resets. The leakage current also increases the system
noise. However, the SVX4 uses correlated sampling, measuring the
pedestal on the first quarter of every clock cycle and the signal on the
remaining three-quarters of the cycle. Therefore the noise increase is
only due to the jitter on the injected electrons over a single 106 nsec
cycle (6000 electrons \~ 80 electrons) which is less than 0.1% of the
expected signal size. Furthermore, the leakage current can be reduced by
cooling the sensors. Sensor/SVX4 tests with and without external
capacitive coupling will be made to test this conclusion.

Some sort of pitch adapter is required to bring the bonding pads of the
sensor and the SVX4 into registry. To save space it may make sense to
incorporate the pitch adapter directly into the sensor. One possible
option is shown in Figure 42, below. This would eliminate dead space at
the sensor z-boundaries and would also not consume precious real estate
with a pitch adapter. Furthermore, this significantly increases the
length of the PC board edge at the z-boundary, where the ROC's are
placed adjacent to each other. Since the ROC's completely cover the
sensor, and since they require ground-planes, power planes and control
signal traces, it is possible to simply daisy-chain those contacts
across the ROC boundaries to form a bus without any extra material. By
bringing the signals in from the side there is more than sufficient room
for the ROC-to-ROC signal and power connections, see Figure 43, below.
(The signal connections are comprised of 8 data lines and 20 control
lines (all differential) which take up 1.2 cm given 100/100 m
trace/space). This leaves nearly 2cm for power and ground connections.

The primary trace count on the ROC's is due to the connections from the
bus to the RCC and from the RCC to the SVX4s. A possible top-level trace
layout is shown in Figure 44, showing that two trace layers (in addition
to some surface traces) should be sufficient.

### Pilot Module

The ROC's need to receive timing and control signals and they need to
send out data. The space available at the end of the ladders (2x3 cm)
and the inaccessibility of this area both argue to put as little
intelligence there as possible. Thus a pilot module, wire-bonded to the
ROC bus at the end of each ladder will drive signals to a remote
Front-End Module, described below. Signals may be driven off the Pilot
Module either on copper (w/ e.g., the rad-hard LVDS transceiver
developed by FNAL for this purpose for the CDF Silicon detector) or on
fiber (with e.g., the Texas Instruments TLK1501, a very-low power 16-bit
serializer/de-serializer chip plus an optical link, an option being
considered for a number of LHC detectors). The fiber option is
especially attractive (reduced cable plant, lack of electrical
connection and consequent grounding concerns, and the ability to put the
FEM's in a truly remote location), but the feasibility of this option
needs to be addressed further.

### Front-End Module

The Front-End Module (FEM) will serve as the interface between the
ladders and the PHENIX DAQ (Serial Control (Arcnet), Clock & Control
(Granule Timing Module), and the Data Collection Module). The FEM's will
be outside of the detector acceptance. They will have the hardware
necessary to link to the different pieces of the PHENIX DAQ and to the
Pilot Modules. They will also have on-board FPGA-based intelligence to
parse the GTM and Arcnet control signals and format the event data. The
code for the GTM and Arcnet control parsing is largely implemented in
the SVX4 test board developed at ORNL. The data formatting code is
particularly simple, and is almost entirely a subset of code developed
for previous PHENIX subsystems. It consists of setting the appropriate
control bits, constructing the event header and trailer, and moving the
16 bits of channel data (which comes in as two 8-bit words on opposite
phases of a clock) onto a single 16-bit word clocked on the leading edge
of a clock. A block diagram of the entire strip FEE is shown in Figure
45 below.

### Zero Suppression

The SVX4 allows for on-chip zero suppression. However, the PHENIX DAQ is
not designed to handle zero-suppression prior to the DCM because the
pipelined architecture assumes a fixed length data packet. However, the
use of this feature has some significant advantages, as described below.

The digitization of the SVX4 ADCs proceeds in parallel and takes 256
clock cycles, regardless of zero-suppression. The data is then read into
the RCCs where it is buffered awaiting the signal that the Data
Collection Modules are ready to receive data. The data from each channel
consists of an 8-bit address and an 8-bit ADC value. Both data transfer
steps on the ROC (out of the SVX4s and out of the RCCs) use 8-bit buses
which transfer the address on the leading edge of a clock signal and the
ADC value on the trailing edge. So at both stages each channel's data is
transferred in one clock cycle.

The readout of each SVX4 on the ROC needs one clock cycle for a header
word and one clock cycle per hit channel (128 \* occupancy). The
occupancy can be considered to be 1 if zero suppression is disabled.
Read out and digitization can be driven by clocks of different multiples
of the beam frequency (9.4 MHz) and must be completed within 0 sec (375
clock cycles). This can be expressed by:

256/M + 6\*(1+128\*occupancy)/N \< 375 clocks,

where M is the digitization frequency in units of the beam clock
frequency, and N is the readout frequency (defined similarly). If we
assume M = N = 1 (e.g., readout and digitization frequencies both equal
9.4 MHz) then the maximum occupancy that would fit in the PHENIX
bandwidth requirement is 14.7%. It is true that if we use readout and
digitization frequencies equal to four times the beam clock frequency
(37.6 MHz, or M = N = 4) we can pass the SVX4 data without zero
suppression into the RCC. However, the readout of the ladder, as shown
below, gives a more stringent requirement.

To read out an entire ladder, which has 48 ROC's, and which similarly
must be completed in 40 sec, we find:

48\*(1+128\*occupancy)/X \< 375 clocks,

where X is the RCC readout frequency in units of the beam clock
frequency. Assuming X = 4 we find that the maximum occupancy is 28%. The
consequence is that we would need to either a) use on-chip
zero-suppression, b) use a significantly higher readout speed, or c)
have more output links per ladder. We have chosen to use the on-board
zero suppression feature of the SVX4 because 28% is more than double the
maximum expected luminosity for the inner barrel in central AuAu
collisions. Therefore zero-suppressed events *should* always fit in the
required length of time (although a mechanism to pass up an error
condition will still need to be developed). A further advantage is that
with zero suppression turned on we can limit the maximum clock frequency
into the SVX4 to 9.4 MHz.

![](media/image51.wmf){width="4.489583333333333in" height="2.5875in"}

[]{#__RefHeading___Toc66641811 .anchor}Figure 40 CDF Hybrid with
dimensions shown. This board contains four SVX4 chips, local power
filtering and traces for power, ground and data/control signals and is
functionally equivalent to the proposed ROC.

![](media/image52.wmf){width="5.995138888888889in"
height="4.589583333333334in"}

[]{#__RefHeading___Toc66641812 .anchor}Figure 41 RCC block diagram. This
chip, implemented as either a rad-hard FPGA or a fully digital ASIC,
serves primarily as a simple, state-driven de-multiplexer. Additionally,
a FIFO is used to buffer digitized data allowing simultaneous
digitization and readout.

![](media/image53.jpeg){width="4.3875in" height="5.076388888888889in"}

[]{#__RefHeading___Toc66641813 .anchor}Figure 42 The top panel shows the
sensor and some representative strips. One possibility for pitch
adaptation is alos shown; an on-board pitch adapter, realized through an
extra metallization layer on the sensor (bottom panel), brings the
signal traces to -edge of ladder. This eliminates dead space along the z
coordinate of the ladder and simplifies the ladder connections.

![](media/image54.wmf){width="4.7in" height="1.89375in"}

[]{#__RefHeading___Toc66641814 .anchor}Figure 43. ROC top layer w/ major
components (SVX4, RCC) and bus connections shown. There are a relatively
small number of additional passive components required, as shown in the
CDF implementation in Figure 40. Two ROC's read out one sensor, a total
of eight are incorporated in one ladder. The figure is drawn to scale.

![](media/image55.wmf){width="3.892361111111111in"
height="2.0208333333333335in"}

[]{#__RefHeading___Toc66641815 .anchor}Figure 44 ROC signal trace
layers. The figure is drawn to scale with bus widths given with a
100/100 m trace/spacing assumption.

![](media/image56.wmf){width="5.992361111111111in"
height="4.188194444444444in"}

[]{#__RefHeading___Toc66641816 .anchor}Figure 45 FEE Block Diagram.

### Si strip production/testing/assembly schedule

The Si strip wafers will be manufactured by a commercial vendor;
Hamamatsu of Japan and Sintef of Norway are currently under
consideration (see Figure 44). At the vendor the wafers will undergo
resistance and doping tests and then be diced into sensors. Further
quality assurance (QA) tests including visual inspection, initial I-V
test, and registration in our database, will be performed on all sensors
produced upon receipt at RIKEN. Sub-samples of the sensors will be sent
to SUNY Stony Brook and UNM for further QA tests including I-V, C-V, and
laser pulse tests of each strip. RIKEN will adapt its automated probe
station for Si pixel detectors to accommodate testing of strip
detectors. SBU and UNM are in the process of negotiating with the high
energy particle physics groups (D0 and CDF, respectively) at their
institutions to use their testing facilities and if they fail, manual
equipment will be set up and employed by post-docs & students. Assuming
a testing rate of one sensor/day the entire process should take a
maximum of four months divided between the three institutions to produce
enough good sensors including spares. With the experience of groups
responsible for QA testing and assembly of Si trackers at D0, CDF, STAR
and PHOBOS serving as guidance, the detailed testing procedure will be
developed.

![](media/image57.png){width="6.129166666666666in"
height="5.129861111111111in"}

[]{#__RefHeading___Toc66641817 .anchor}Figure 46　 Strip detector
production flow chart

As previously stated, enough SVX4 readout chips for Si strip detectors
already exist at FNAL. Further processing of SVX4 chips will occur at
FNAL, including thinning and metallization, initial QA tests, and dicing
prior to purchase by PHENIX. An integrated SVX4/sensor test at ORNL will
occur by April 2004 to determine the viability of this particular
readout combination (see Table 7). A slightly modified version of the
test board developed at ORNL will be used for future system tests
provided this milestone is successfully passed.

ORNL has also assumed primary responsibility for development and
prototyping the BeO ROC's. Each ROC reads out one-half of a Si strip
sensor with six SVX4 chips and has one rad-hard FPGA (or possibly a
custom digital ASIC) to serve as local intelligence to direct SVX4
initialization, digitization and readout. Power planes, ground planes
and control signals, already present on the ROC's, are daisy-chained
across the ROC's to form the strip bus. A first test of a fully
functional prototype ROC (all components, but no attempt at
miniaturization or thinning) is slated to occur by Oct. 2004 (see Table
7).

[]{#__RefHeading___Toc66641836 .anchor}Table 7 Si strip detector test
schedule

  ---------- ------------------------------------ -----------------------
  **Date**   **Test**                             **Location**

  Apr. 2004  Si Sensor/SVX4 on the testboard      ORNL/RIKEN/BNL

  Oct. 2004  Full ROC (SVX4/FPGA/strip bus)       ORNL

  Dec. 2004  Si sensor/full 1^st^ round ROC       RIKEN

  Jul. 2005  Si sensor/full 2^nd^ round ROC       RIKEN & SBU

  Jul. 2006  1^st^ full ladder                    RIKEN
  ---------- ------------------------------------ -----------------------

PCB fabrication for the ROC will occur at a commercial vendor, e.g.
Zentrix, from the gerber file produced by ORNL. Mounting and
wire-bonding of the SVX4s and ASICs will also occur at a commercial
vendor, using a parts list with x-y locations specified for each
component by ORNL. ORNL will be the technical point of contact
throughout the entire production, assembly and testing of the Si strip
ROC's. Because a ROC mounted on the Si barrel will be extremely
difficult to replace once installed in PHENIX, very strict quality
controls are necessary during testing of the production boards. This
tight QA procedure will involve an initial system test. Since there are
less than 400 ROC's and all chips will pre-qualified, the duration of
these tests will likely be limited by the startup time for the test
system, although that system should be largely developed during the
testing of pre-production prototype ROC's. This initial test will be
followed by an extended burn-in period and a re-testing. Presumably,
students and postdocs would participate in this process. With 336 ROC's
in the final system, a requirement for 10% good spares and an
anticipated initial failure rate of 10% a total of 400 ROC's will be
manufactured. Qualified ROC's will be sent to RIKEN and SBU where they
will be mated with qualified sensors. RIKEN is about to purchase an
automatic wire bonding machine which is operational in the middle of May
2004, while Stony Brook is in the process of procuring one. An initial
test of the sensor plus ROC assembly is scheduled for Dec. 2004 at
RIKEN.

Each ladder receives its serial programming, clock & control signals and
sends its data signals through a pilot module mounted at the end of the
ladder to a remote front-end module. This module is relatively simple,
basically only serving to drive signals into and out of the active area
with as little mass and volume as possible to the downstream processing
system. These modules will be fabricated and assembled by a commercial
vendor, similar to the ROC's. Pilot modules will be tested at ORNL with
known-good ROC's and sent to RIKEN and SBU for assembly onto a ladder.

Qualified ROC/sensor assemblies and qualified pilot modules will be
assembled into ladders and undergo complete system tests at RIKEN and
SBU. A first full ladder test should be ready by the middle of 2006.
Table 1 summarizes the test schedule for Si strip detectors.

The QA procedures and criteria for acceptance and failure of the strip
sensors and the ladders will be developed drawing on the significant
amount of experience already in place at UNM and Stony Brook (in the
high energy physics groups) involved in CDF and D0/ATLAS, respectively.
RIKEN plans to train some of their young student scientists under the
guidance of the Stony Brook D0 group preparing for their L0 Si detector
upgrade during the middle and latter half of the 2004.

The details of QA criteria for the strips and ladders will be developed
in due course in consultation with the vendors, the understanding of
each of the components as prototypes are made, and in consultation with
the experienced groups in high energy physics in this field. The QA
criteria for the strips and the ladders will be separated in to two
categories: The criteria for dimensional or mechanical properties and
electrical properties.

The QA for mechanical properties will include physical dimensions of
sensors and ladders, thicknesses and the widths along the length of the
strips and ladders, edge chipping due to cuts and related tolerances,
alignment at various joints including metallization with implant. These
other such criteria can be tested using a detailed visual inspection
or/and optical metrology.

The QA for the electrical properties will include measurements of
following properties to be within a certain tolerance limits. They
include for example, the CV and IV curves, the leakage current on strips
(I~strip~), the inter-strip resistance (R~int~), and the inter-strip
capacitance (C~int~) at a specific frequency.

Both types of tests, mechanical and electrical, will be further
separated in to three types:

1.  Key tests: These will be performed on every sensor and every ladder
    assembly. These are most important because they determine the
    minimum performance of the strips and ladders as individual
    entities.

2.  Subset test: These will be performed on a defined fraction of strip
    sensors and ladders, which pass the key tests. The main goal of
    subset tests is to verify compliance with specification in depth.
    Typically, the fraction of sensors and ladders that will undergo
    this tests will be higher during the early stages (or prototypes)
    and in the production stage depend on the overall experience of the
    quality of production and some key correlations to be developed at a
    later stage with the vendor QA data. The subset tests will be done
    with the automated probe stations under computer control.

3.  Diagnostics tests: These will be done on a fraction of strips and
    ladders on a fraction of units passing the Key tests, and also on
    the units flagged

The frequency of subset tests and diagnostic tests will be determined as
we proceed through the prototyping process.

Two other issues not mentioned up to now but assumed is that all testing
will be done in a controlled environment, i.e. in clean rooms meeting
criteria specified by the vendor. All personnel handling the sensors and
ladders shall undergo training & practice in all phases of manipulation
involved in the process. There will also be a clean & dry storage
facility for ladders not being tested or used. The clean rooms will
control the temperature and humidity. The second issue is keeping a good
record of the environmental conditions for each tested sensor and ladder
in a complete database. The database will include will include not only
the results of the QA associated with a particular sensor/ladder but in
addition the temperature and humidity, date, testing center, and any
other comments that the testing crew deems important at the time of the
test.

RIKEN will copy the laser test setup from BNL Instrumentation for this
purpose and an identical setup will be moved / set up at BNL Chemistry
for final QA tests before the completed ladders are assembled onto the
barrel frame.

## 4.4 Mechanical Structure and Cooling {#mechanical-structure-and-cooling .unnumbered}

A conceptual design of the silicon vertex detector was commissioned by
the LANL group to HYTEC, Inc. HYTEC is the mechanical designers for the
ATLAS silicon group and has 15 years of design experience with silicon
vertex detectors. For PHENIX they have also designed the station-1 muon
detectors and the station-2 spider and also did the finite element
analysis of the station-3 octants. The VTX mechanical conceptual design
was finished and the report is summarized in this section.

\[<http://p25ext.lanl.gov/~hubert/phenix/silicon/HTN-111003-0001.pdf>\].

The next steps following this conceptual design are to fully specify the
requirements for the VTX mechanical support and cooling. These
requirements will incorporate the integration needed for all the upgrade
PHENIX detectors in the inner region, including the VTX barrel described
in this proposal, the end-cap described in Appendix A, and the HBD/TPC
to proposed later. Hence there are two major mechanical engineering
tasks contained in this proposal: 1) the internal support and cooling of
the VTX detector (described in this section) and 2) the integration of
the VTX detector into the inner region of PHENIX (described in the next
section).

For the internal support and cooling of the VTX detector, the major
results of the conceptual design are:

-   The use of sandwich composites will satisfy the radiation length
    requirements and provide the required stiffness.

-   The outer frame structure should be a single diameter encompassing
    both the barrel and end-caps.

-   The modular clamshell design can satisfy the stability requirements
    provided the connection issues are studied further.

-   An octagon arrangement is suggested to facilitate utility routing
    and fabrication.

-   Structural end disks at either end of the structure are recommended
    to prevent deformation

-   The ladders should have a simple support at one end and floating
    support at the other end to minimize thermal strains

The R&D issues identified are:

-   Building prototypes of ladder assemblies to verify calculations.

-   Building full-scale prototype to test static and dynamic stiffness.

-   Develop connections of modules.

-   Develop support design.

-   Refine calculations and develop full concept for 0 deg operation if
    necessary.

### Design Criteria

The goal of the study is to establish a feasible design and to identify
outstanding design issues. The study is based on a preliminary list of
design requirements and a straw-man layout of the detector structure. To
adequately address all structural and mounting issues a fully integrated
design, which includes the barrel detectors and future end-caps
extension, is needed. This design needs to address all integration
issues not only for the barrel and the end-cap vertex trackers, but also
with other potential PHENIX upgrades.

The design requirements of the conceptual study were,

-   Modular Design

    -   End-caps detectors can be mounted independently at a later time

    -   Support structure separated vertically into two half shells

-   Detector Coverage

    -   Hermetic design

    -   Four barrel layers

    -   Four end-cap layers in each forward section

    -   Fiducial volume \< 20 cm radius, z \< 40cm

-   Radiation length goal \< 1% per layer

-   Room temperature operation desirable, 0 deg Celsius if needed

-   Dimensional stability \< 25 microns

In the conceptual study, the ALICE1LHCb pixel hybrids for the inner
layer and silicon strip detectors with SVX4 readout for the three outer
layers provide the basis for cooling and radiation length analysis of
the barrel detector. At the time, for the end-caps a modified ALICE type
chip that has 1/5 to 1/10 of the number of pixels was assumed[^37].
These choices resulted in a estimated heat load of typically 0.7 W/cm^2^
for the barrel and 0.1 W/cm^2^ for the end-caps.

### Structural Support

The selection of materials for the support structure is based upon the
above criteria where the most important material properties are high
radiation length, low density, high stiffness, and availability. Out of
three candidates (i) beryllium, (ii) graphite fiber reinforced plastic
(GFRP), and (iii) Carbon-Carbon, the GFRP was chosen for the study
because of its wide availability, works well in sandwich composites, and
has good radiation length and strength properties.

#### Structural Analysis

The structural analysis includes two studies, a first study using finite
element analysis models and the resulting modal frequencies to look at
dynamic stiffness of tracker concepts and a second study to look at the
static stiffness with mass loaded structures. The lower modal frequency
limit is set at 70 Hz on a fully loaded structure so that the natural
frequencies due to environmental conditions such as pumps, traffic, etc.
do not couple into the structure and cause instabilities greater than 25
microns.

![](media/image58.png){width="5.997916666666667in"
height="1.5319444444444446in"}

[]{#__RefHeading___Toc66641818 .anchor}Figure 47 Design concepts studied
for the vertex detector support structures. The center most concept with
the constant outer diameter shell had the highest fundamental frequency.

![](media/image59.jpeg){width="2.875in"
height="2.0069444444444446in"}![](media/image60.jpeg){width="2.873611111111111in"
height="1.975in"}

[]{#__RefHeading___Toc66641819 .anchor}Figure 48 　First mode shape that
dominated the dynamic structural stiffness analysis

Various support structures shown in Figure 47 were studied. The center
most structure has the highest frequency limit.

The dumbbell shaped structure has the lowest mode frequencies below 53
Hz while the concept with the uniform shell with constant outside
diameter has the lowest fundamental mode at 132 Hz, well above 70 Hz. In
Figure 48 the associated first mode shape of the concept that has the
highest fundamental frequency is shown

The static analysis under gravitational load is shown in Figure 49 for
the concept with the uniform shell. A 1.0 G load is applied vertically
to the fully loaded structure. The maximum displacement is 14.5 microns
and the maximum stress is 130 psi. These satisfy the design criteria so
the uniform shell with constant diameter has been chosen as the concept
to be pursued.

![](media/image61.jpeg){width="2.748611111111111in"
height="1.8930555555555555in"}![](media/image62.jpeg){width="2.748611111111111in"
height="1.8930555555555555in"}

[]{#__RefHeading___Toc66641820 .anchor}Figure 49 Displacement and
principle stress from a 1.0g gravity load on a full mass loaded
structure

### Detector Ladders and Cooling 

The mechanical design draws on a ladder concept for supporting both the
inner layer of pixel and the outer strip detector layers. The pixel
detectors and strip detector array are arranged in a longitudinal
fashion, and at a slight cant angle, which provides a small amount of
overlap for hermeticity. The pixel and silicon strip detector both
contain on-board electronics, thus necessitating cooling along the
Z-axis of the detectors, thus the ladders simultaneously must provide
mechanical support and cooling.

The barrel region is about 30cm in length and thus the ladders need
supported only at their ends. Open ring like structures at the two ends
of the ladders, Figure 50, provide attachment points for the ladders and
serve to combine the staves into two halves of a clamshell. Figure 50
also illustrates the cross section of a ladder structure, it is composed
of a thermal plane (Carbon-Carbon) onto which the pixel modules or strip
detectors are mounted. The thermal plane collects the distributed
electronic heat, as well as providing a conductive path to the cooling
tube. All elements are bonded with thermally conductive, rigid setting
adhesives. The omega shaped piece holding the cooling tube on to the C-C
thermal plane provides significant stiffness to the ladder.

![](media/image63.jpeg){width="2.748611111111111in"
height="1.8854166666666667in"}![](media/image64.jpeg){width="2.126388888888889in"
height="0.7576388888888889in"}

[]{#__RefHeading___Toc66641821 .anchor}Figure 50 3D model of the barrel
region on the left and the ladder structure on the right showing a
cooling tube mounted on a C-C thermal plane and the sensor and
electronics on the underside.

#### Cooling Analysis

The total heat load that must be removed from the vertex detector is
approximately 2.2 kW, which is dominated by power dissipation in the
barrel detectors. There are generally two choices for the coolant
system, single-phase and two-phase. In a single-phase system the coolant
is circulated through pipes in a closed system. In a two-phase system
the coolant arrives as a liquid and then evaporates into the detector
volume where it is collected and removed. The two-phase system has the
advantage that it is a more efficient coolant and a lower total mass is
required. However, the two-phase system is more difficult to implement
because of issues concerning more sophisticated temperature and pressure
control. The single-phase system is simpler in implementation and design
and therefore chosen to be the baseline design.

An important issue in the design of the mechanical structure is the
operating temperature. In the initial design requirements we stressed
the importance of room temperature operation and the design presented
here is based on this assumption. However, the design engineers have
developed the concepts that will allow operation at 0 deg by using
suitable coolants that can operate at these lower temperatures. A more
detailed study of the enclosure and thermal stresses would need to be
done to confirm the concepts at reduced operating temperature. After
this study was concluded, it was noted that the outer 3 layers of the
barrel might perform better at 0 deg because of the mismatch between the
SVX4 chip which is an AC coupled device and the strip sensor which is a
DC coupled device. The concern centered on leakage currents from the
sensor that could saturate the SVX4 chip. The other option is to reset
the chip regularly during the empty beam-crossing at RHIC.

The selection of coolants was based on previous experience in the design
of the ATLAS detector and the choice was to use one of several
perfluocarbon candidates, commonly called fluorinerts. These fluids can
be used in either a single or a two-phase system and are environmentally
acceptable. Based on a number of considerations the fluorinert C5F12 was
chosen as the baseline.

In comparison to the ATLAS detector the heat load is very modest and a
single-phase system can be used. Since the barrel is only 30 cm long the
design assumes that the ladders need only be supported at the ends and
the cooling structure can serve as the means of joining the two half
ladders of the pixel layers.

The concerns with this approach center on,

-   Out of plane distortions from thermal strains due to different CTE's

-   Gravity sag

-   Mass of the structure exceeding radiation length guidelines

A series of calculations were done on the thermal aspects of this
concept by using the outer barrel ladders since the greatest total heat
load, 27 W, exists there. Using a temperature rise of 2 deg C as the
maximum allowed temperature rise in the ladder the results indicate a
good solution exists with an Al tube diameter of 3mm and a wall
thickness of 0.2 mm.

The result for the out-of-plane distortions for room temperature
operation is quite acceptable, 0.18 microns. For the possible design
requirement of 0 deg operation the out-of-plane distortions increase
because of the difference in CTE's of the C-C and silicon but is still
acceptable at 3.5 micron. Bowing along the length of the ladder due to
thermal strain because of the temperature gradient at room temperature
is an acceptable 6.8 microns. However, if the detector is cooled, the
bowing increases to over 80 microns. This is more than desirable so
addition R&D is necessary.

![](media/image65.jpeg){width="2.8722222222222222in"
height="1.6118055555555555in"}![](media/image66.jpeg){width="2.997916666666667in"
height="1.53125in"}

[]{#__RefHeading___Toc66641822 .anchor}Figure 51 Left panel shows the
out of plane distortions and the right panel shows the bowing for the 0
deg solution.

Figure 51 illustrates the 0 deg solution. While the temperature drop for
the coolant is still the same as at room temperature the reference
temperature is always 25 deg since that is the temperature of assembly.
The increased bowing is due to reducing the operating temperature to 0
deg.

For the gravity sag the general bowing of the ladder is acceptable at
18-20 microns.

### Radiation Length

The radiation length budget for the ladder describe above exclusive of
the sensor and electronics consists of:

-   Composite thermal backplane

-   The cooling tube and tube support

-   The omega piece

-   The coolant

The combined radiation length is 0.7% with the single largest
contributor being the tube support (0.28%). The liquid coolant
contributes 0.074%, cooling tube \~0.1%, and the omega piece and C-C
facings \~ 0.2%.

## 4.5 Detector integration into PHENIX  {#detector-integration-into-phenix .unnumbered}

Once the individual detector components and the mechanical support
structures become available, the VTX system needs to be assembled,
integrated into the PHENIX setup, and connected to the support and
ancillary systems as well as to the DAQ. These steps are critical for
the successful completion of the project and need to be addressed well
in advance and in close contact with the developments of the detectors
and support structures.

### VTX detector assembly 

Each step from delivery of sensors and readout chips, to the assembly of
detector ladders, to their final mounting in the mechanical support
structure, will require intensive quality control and testing of the
components. Special equipment, infrastructure and expertise are
necessary to complete these tasks. We have started to plan the necessary
steps and to optimize the use of expertise within our collaboration and
the institutions that we cooperate with.

### Error Budget

Our general philosophy will be to utilize fixtures wherever possible to
allow the assembly of the VTX to be within the tolerances established by
simulations. This will be accomplished by adhering to a strict error
budget. The errors can be separated into intrinsic errors due to the
strip width and assembly errors. The intrinsic error due to strip width
is simply width/12 = 23m for an 80 m micron strip. The assembly errors
are due to the following,

a.  locating the sensors to the precision alignment pin holes on the
    ladders

b.  placing the ladders onto the structural frame

c.  placing the assembly into the hermetic enclosure.

By using precision fixtures we will minimize these assembly errors to \<
10 m each. A precision drill fixture can be used to drill the pin hole
on the ladders and in the structural frame. The structural frame will be
held rigidly in a fixture that will allow positional changes during
ladder installation.

### Ladder Assembly - pixels

The goal of the assembly procedure of the ladders is to insure that the
sensors are accurately located on the cooling supports with respect to
the alignment pins. This will allow manual placement of the ladders on
the structural assembly. The bump bonding will be done at an industrial
facility, VTT. All necessary steps in testing of the bump bonded sensors
will be carried out at CERN or at facilities of the RIKEN institute. For
the silicon pixel detectors the major steps that need to be taken are,

-   Test sensor assemblies which include one sensor and 4 readout chip.

This test will require a full miniDAQ and cooling system at each testing
facility. Since the readout buss will not be attached yet, a probe
station will be used. A fixture will be required that will allow the
chips to be cooled without being glued.

-   Attach readout bus to pilot card and test.

-   Attach readout bus and pilot card to sensor assemblies and test.

-   Assemble half ladders, combining readout bus, two sensor assemblies
    and pilot module and test. This is the most critical mechanical
    operation in assembling the VTX. The sensors must be attached to the
    ladder with an accuracy of \<10 m.

This can be done by either a very sophisticated fixture such as the one
designed by the ALICE group or by an accurate pick and place machine.
The alignment pins will be the fiducials.

### Ladder Assembly -- strips

.

For the testing of the strip sensors and the SVX4 chips, we will benefit
from the knowledge of the BNL Instrumentation Division and the
cooperation with the FNAL silicon laboratory. The ORNL group, which is
developing the ROC, will work together with other groups, including
University of New Mexico, to test and assemble the ROC's. The University
of New Mexico group draws on knowledge and experience gained during
similar work for the ATLAS and CDF vertex detectors

For the silicon strip detectors the major steps that need to be taken
are:

-   Fully test sensor at the BNL laser test stand.

-   Fully test the SVX4 chips at the Fermilab electronics test facility

-   Test bare readout card

-   Mount SVX4s on ROC's

-   Test ROC assembly. This will require cooling fixtures for the chips
    and miniDAQ's at all fabricating institutions

-   Attach ROC's to sensor

-   Send to wire bonding facility, commercial (?)

-   Test ROC/sensor combo

-   Assemble ROC/sensors into ladders. This will be done in manner
    similar to that done for the pixel detectors.

-   Attach pilot modules to ladder

-   Test complete ladder, needs complete cooling system and miniDAQ.

### Half detector assembly

All fully tested ladder assemblies, pixel and strip will be received by
the BNL/Stoney Brook and retested to insure that nothing was damaged in
transport. The ladders will be inserted into the structural assembly
beginning with the innermost layer proceeding to the outermost layer.
The structural assembly will be securely held in an accurate holding
fixture that will allow the structural assembly to be rotated so the
ladders can be placed on the pins and fastened into place by either
screws or glue and an accurate survey can be conducted and recorded. A
final test of the completed half detector will be done under a full
system test, full cooling and readout. If ladders are shipped to the
assembly in small lots then much of the VTX assembly can be done in
parallel to the ladder production.

### Integration into PHENIX

#### Mechanical mounting

The mechanical mounting of the detector will be done by BNL PHENIX
Operations, in close collaboration with HYTEC. The current concept would
be similar to the existing PHENIX MVD mounting. This will support the
VTX detector directly on the copper nose cones with attachments to the
ends of the detector. The two halves of the split barrel will be either
hinged together at the top or the bottom, or be mounted independently.

The development of this concept will require careful consideration of a
number of issues, including precision and stability requirements,
accommodation of future detectors (e.g. silicon vertex detector end-caps
to cover the muon detector acceptance, and a micro Time Projection
Chamber (TPC) in the acceptance of the central arms), the attachment and
routing of cables, fibers and hoses. Figure 52 shows how the vertex
tracker is placed with other proposed upgrade detector in PHENIX in a
small space inside of the PHENIX central magnet.

![](media/image67.png){width="5.997222222222222in"
height="4.634027777777778in"}

[]{#__RefHeading___Toc66641823 .anchor}Figure 52 The inner region of
PHENIX central magnet with the envelopes of proposed upgrade detectors.
The silicon vertex tracker (SVXT), a micro TPC, and nose cone
calorimeters are shown.

#### Support and Ancillary Systems

Additional platforms installed on top of the PHENIX central magnet yoke
will be required to support electronics racks and cooling system
equipment. These racks will include space for low voltage and bias
supplies, and whatever readout electronics for the silicon detectors.
The platforms must also provide area for cooling system pumps, and
compressors or chillers. In addition, these platforms will be used for
ancillary systems in future detector upgrades in the central magnet such
as the HBD.

#### Beam pipe

A new beryllium beam pipe with a smaller 4 cm inner diameter and 500 m
nominal thickness will be critical to perform the anticipated
measurements. The inner surface of this pipe may need to be NEG
(non-evaporative getter) coated to help reduce beam induced vacuum
instabilities. This technology is currently being implemented in the
upcoming RHIC run. The new beam pipe will need to taper out to match the
standard 5 in diameter lines of the RHIC rings.

### DAQ 

The VTX readout system will be matched to the requirements of the PHENIX
high rate data acquisition (DAQ) system. The current DAQ system has a
bandwidth corresponding to approximately 12.5 kHz level 1 (L1) trigger
rate with a planned upgrade to 25 kHZ. Currently each front-end module
(FEM) sends uncompressed events of fixed length to Data Collection
Modules (DCMs) through a gigabit optical link. Each DCM has four sets of
optical receivers, FPGAs and digital signal processors (DSP), which
zero-suppress and buffer the events from four FEM's. An additional DSP
is used to merge the data from the four sets. The DCMs and FEM's
pipeline events with the capability to buffer at least 4 or 5 L1
triggers. Since the FEM data is of known length no data flow control
between FEM's and DCMs is necessary in this design and only the DCM
participates in the busy logic.

Because the VTX will deliver substantially larger data volumes than the
currently operated detectors and it will be necessary to zero suppress
the data at the front-end before it is transmitted to DCM\'s. As a
consequence some of the current DCM-functionality must be taken over by
the pilot modules on the detector and the FEM's off the detector. In
particular, after the zero suppression, the FEM data will no longer be
of fixed length and therefore the FEM's must participate in the busy
logic.

Since the new requirements are common to most of the planned PHENIX
upgrades detectors we have launched an R&D effort to develop the new
DCM\'s independent of this proposal. We anticipate that the development
will be completed within 2 years, in time to produce new DCM\'s for the
VTX detector. Once the new DCM\'s are completed the PHENIX Electronics
Facilities and Infrastructure (EF&I) and Online Computing Systems (ONCS)
groups will guide the electronic integration and readout of the VTX.

# 5. R&D

With the help of institutional contributions it was possible to maintain
a small, but well focused, effort over the past two years to explore
technologies for silicon detectors suitable for PHENIX. The results of
these investigations are the basis of the present proposal. The outcome
and corresponding technology choices, which are the ALICE silicon pixel
hybrid detectors and a BNL silicon strip sensor with SVX4 readout, have
been discussed in section 4. More recently the R&D effort has shifted
towards adapting the technologies to the PHENIX requirements. In part
this is possible due to the support PHENIX received following a request
to BNL management for generic R&D funds. Several key issues remain open
and need to be address. The issues fall into two categories, the first
one concerns the readout speed of the pixel ladder and the second one
the readout scheme for the strip detectors.

The readout speed of the ALICE1 pixel chip is limited to 10 MHz, which
means that it takes 25.6 s to read one chip. A sequential readout of all
chips on a ladder, like it is done in ALICE, is out of question since it
does not meet the PHENIX design specification to read each detector in
40 s. Several options to overcome this limitation are under study. They
all involve parallel readout on the ladders, which requires the
development of a new readout bus for the ladder to replace the existing
ALICE one. This is a main focus of the R&D ongoing at the RIKEN
Institute. In addition, a different scheme for the digital pilot must be
used. We are investigating three options:

-   Four Alice pilot cards per ladder

-   Modified pilot card with new digital pilot ASIC based on the ALICE
    technology

-   Modified pilot card with new digital pilot based on rad-hard FPGA
    technology

Design studies for the ASIC option are underway in close collaboration
with the ALICE group. A modified ASIC will be developed at CERN together
with the designers of the original pilot chips. A promising alternative
which would avoid the ASIC development is the use of radiation hard FPGA
technology which recently became available and is intrinsically more
flexible. A first design of the FPGA code is completed and is currently
being evaluated. We plan to make the final technology choice in the
second half of 2004.

The second issue concerns the readout of the BNL silicon strip sensors.
First prototypes sensors have been tested in the laboratory and in beam.
The performance is very encouraging, however, some limitations have been
found which we believe result from poor signal-to-noise ratio resulting
from the initial sensor design and the readout electronics used. The
next generation of improved prototypes will be tested with the SVX4, our
preferred choice for the readout chips, in early 2004. Based on the
information at hand and multiple discussions with the experts at FNAL,
ORNL, and BNL instrumentation this combination should provide the
necessary performance.

A key issue for the use of the SVX4 readout chip is the development of
an appropriate readout card (ROC) that matches the PHENIX
specifications. A first schematic design has been developed, which
integrates six SVX4 chips, two custom ASIC readout controller (RCC) and
the readout and control bus on one card matching the a strip sensor in
size. The development of a prototype is about to start, and we expect to
test a full version by October 2004.

For many parts of the VTX, the technology choices have been made, and
R&D is focusing on prototyping the designs. We need to pursue and
complete these topics over the next year to start EDIA and construction
of the VTX in FY05. Generic R&D funding through both RIKEN and from the
DOE will be required to complete these tasks. In detail the projects
are:

*Inner Pixel layer*

-   Pixel Bus, multiple layers, fine lines on Kapton

    -   Uses ALICE bus as starting point

    -   Draws on rapid advances in signal interconnect technology

    -   Design and prototyping completed by Sep 2004

    -   RIKEN manpower

-   Pilot Module

    -   Uses ALICE pilot card as starting point, containing existing
        ALICE analog PILOT and optical chips, and either the new FPGA or
        ASIC digital pilots.

    -   Technology decision by Sep 2004

    -   RIKEN, ISU manpower

-   Pixel FEM

    -   First prototype complete by Oct 2004

    -   SBU manpower

*Outer Strip Layers*

-   Readout card for SVX4

    -   First test of full prototype by October 2004

    -   RIKEN, ORNL manpower

-   Serpentine strip sensor

    -   Second prototype tested with SVX4 by April 2004

    -   RIKEN manpower

*Auxiliary System and Integration*

-   Specifications of mechanical design

    -   List of design parameters by July 2004

    -   BNL/LANL/HYTEC manpower

-   Design study

    -   LANL/HYTEC manpower

# 

# 6. Project management and responsibilities 

The organization and management of the proposed effort is embedded in
the management structure of the PHENIX experiment, which is part of the
BNL RHIC project. The new organization must satisfy a number of
requirements including a clear interface to the existing RHIC and PHENIX
management structure, clear roles and responsibilities within the
existing PHENIX subsystem structure. Particular attention has to be paid
to the fact that a significant portion of the project is supported by
foreign contributions. Clear deliverables, responsibilities for
deliverables and the accountabilities of the participating funding
Agencies have to be defined. These responsibilities will be formalized
in memoranda of understanding (MOU\'s) between PHENIX and the
participating institutions. In this section, we outline our proposed
management organization and delineate responsibilities within the
project.

## 6.1 Project background {#project-background .unnumbered}

The proposed project is part of a detailed upgrades program to enhance
the physics capabilities of PHENIX over the next 8 years. Realizing this
plan will enable PHENIX to remain competitive well beyond the turn on of
LHC expected for 2008, as well as to advance our understanding of QCD by
fully exploiting the unique spin physics capabilities of RHIC. The plan
covers a broad range of measurements in AA, pA, and pp and its goal is
to provide key measurements which currently can either not be addressed
at RHIC or only with limited accuracy.

The development of the PHENIX upgrade program started in response to the
recent NSAC long-range plan, which was developed in 2000. The strategy
was consolidated at a workshop in Montauk, NY March 2001 and at BNL
August 2002. Since then individual upgrades have been followed up in
detail within four PHENIX study groups.

The PHENIX upgrades plan was first presented to BNL management in a
proposal seeking funds to initiate a broad-based R&D effort to develop
the detector technology necessary to realize our goals. BNL charged a
Detector Advisory Committee (DAC) to review the R&D plan. After the
review December 19-20, 2002, at BNL the committee named the PHENIX
silicon vertex tracker a high priority in the future development of
PHENIX. Some quotes from this report:

\"Physics Motivation: ... Charm has emerged as valuable probe of QCD
dynamics ... The measurement of hadrons with open charm requires
excellent vertex identification, which can only be achieved with state
of the art silicon vertex detectors ...\"

\"PHENIX Microvertex Tracking Detector: The extension of the
capabilities of the PHENIX detector to provide a direct measurement of
charm and open beauty will have major impact on a number of physics
questions both in AA and pp collisions. This upgrade is therefore a very
high priority in the future development of PHENIX."

"It is likely that a detector system with adequate performance can be
constructed using existing technology and it is therefore possible and
desirable that a detailed proposal for this upgrade be in place in time
for inclusion in the planning process for FY05 construction funds.\"

Responding to the DAC review, the silicon study group developed a PHENIX
internal letter of intend proposing a two component silicon vertex
tracker system, one component - a barrel detector - extending the
capabilities of the PHENX central arm detectors and the other - a
end-cap detectors - extending the physics reach of the muon detector
system. This LOI was reviewed in March 2003 at a joint meeting of the
PHENIX detector council (DC) and executive council (DC). Following their
recommendations PHENIX management (PM) endorsed both projects and
charged the silicon study group to develop a proposal for a silicon
barrel detector for immediate presentation to DOE through BNL.

The DAC met again on Nov 22-23 2003 and reviewed a preliminary version
of the VTX proposal. The committee report stated that "the Collaboration
has made impressive progress.... and a viable design is close." They
made seven recommendations that we have since addressed in this
proposal: 1) concern on the occupancy of the 2^nd^ layer, 2) explore the
possibility of reducing the number of technologies, 3) need for a system
test between svx4 and strip sensor to evaluate signal/noise, 4) utilize
the Si expertise at BNL, 5) define more the organization structure and
responsibilities, 6) include more details in the schedule on the system
tests during prototyping and details on the final assembly and QA of the
sensors, electronics and ladders, and 7) document the schedule for
performing a "ladder" test which includes sensor, electronics, bus,
readout and mechanical ladder. Each of these concerns has been addressed
in this proposal.

## 6.2 The management plan for the VTX {#the-management-plan-for-the-vtx .unnumbered}

### PHENIX management structure

The VXT project is part of the PHENIX project and as such integrated
into the PHENIX management structure as described by the PHENIX bylaws.
The PHENIX Detector Council (DC) will advise PHENIX management on the
design, construction, and integration of the VXT. The DC is co-chaired
by the operations manager (E.O\'Brien) and the upgrades manager (A.
Drees). The VTX subsystem manager will serve as a member of the DC.

### PHENIX subsystem leadership

We expect that the proposed VTX project will be funded through two
agencies, the DOE Office of Nuclear Physics (DOE-NP) and the RIKEN
Institute. A successful completion of the VTX will require close
collaboration and well-defined responsibilities and scope of the
contributions of both agencies in terms of deliverables. The
deliverables and foreign contributions are outlined below. Within
PHENIX, the responsibility for the VTX subsystem will be shared by the
subsystem leader, Yasuyuki Akiba (RIKEN) and his deputy, Craig Ogilvie
(ISU). The subsystem leader reports to PHENIX PM and will represent the
VTX in the PHENIX DC.

Simultaneously, Ogilvie will serve as the DOE contract project manager
(CPM), and will have the fiscal and construction responsibility for the
DOE funded deliverables as outlined in this proposal. This involves
appropriate planning, budgeting, and reporting. Akiba will serve as
RIKEN counterpart and have similar responsibilities for the RIKEN funded
deliverables.

### Role of BNL

Because we expect that all DOE funding for this effort will be directed
through the BNL Physics Department, BNL line management will have
ultimate fiscal and management responsibility for the construction of
the VTX and for its subsequent operation.

![](media/image68.wmf)

[]{#__RefHeading___Toc66641824 .anchor}Figure 53 Management chart of the
VTX project. The fiscal responsibilities for the individual tasks are
specified in bold letters. The intitutions participating in each task
are given in italic. In PHENIX the DAQ is a separate subsytem and
therefore not connected to the VTX management.

Included in the management chart is the position of Lead Electronic
System Engineer. This person has responsibility to oversee the
electronics integration of both strips and pixels and will be funded
with construction dollars. The ideal candidate is one with extensive
experience with Si detector projects.

More details on the management personnel can be found in Table 8.

[]{#__RefHeading___Toc66641837 .anchor}Table 8 Professional Background
of the lead managers in the VTX project.

+------------+----------------+---------+----------+------------------+
|            | People         | VTX FTE | VTX FTE  | Experience       |
|            |                | 2004    | after    |                  |
|            |                |         | 2004     |                  |
+------------+----------------+---------+----------+------------------+
| Management | Subsystem      | 100%    | 100%     | Managed          |
|            | Leader         |         |          | construction and |
|            |                |         |          | installation of  |
|            | Yasuyuki Akiba |         |          | RICH for PHENIX, |
|            | (RIKEN)        |         |          | approximate      |
|            |                |         |          | budget \$10M.    |
|            |                |         |          | Physics Working  |
|            |                |         |          | Group convenor   |
|            |                |         |          | for PHENIX       |
+------------+----------------+---------+----------+------------------+
|            | Deputy         | 50%     | 100%     | Led PHENIX       |
|            | Subsystem      |         |          | Silicon study    |
|            | Leader         |         |          | group. Managed   |
|            |                |         |          | construction,    |
|            | Craig Ogilvie  |         |          | installation of  |
|            | (ISU)          |         |          | multiplicity     |
|            |                |         |          | counter for E866 |
|            |                |         |          | AGS. Physics     |
|            |                |         |          | Working Group    |
|            |                |         |          | convenor for     |
|            |                |         |          | STAR and PHENIX  |
+------------+----------------+---------+----------+------------------+
|            | Project System |         | 100%     | Full-time        |
|            | Engineer       |         |          | electrical       |
|            |                |         |          | systems engineer |
|            | TBD            |         |          | with Si detector |
|            |                |         |          | experience to    |
|            |                |         |          | oversee          |
|            |                |         |          | electronics      |
|            |                |         |          | integration of   |
|            |                |         |          | strips and       |
|            |                |         |          | pixels           |
+------------+----------------+---------+----------+------------------+
|            | Inner Layer    | 50%     | 100%     | Leading RIKEN    |
|            | Manager        |         |          | group at CERN    |
|            |                |         |          | testing and      |
|            | Hiroaki        |         |          | assembling pixel |
|            | Ohnishi        |         |          | detector for     |
|            |                |         |          | NA60 and ALICE   |
+------------+----------------+---------+----------+------------------+
|            | Outer Layer    | 50%     | 100%     | Several years    |
|            | Manager        |         |          | experience in    |
|            |                |         |          | PHENIX, managed  |
|            | Abhay          |         |          | design and       |
|            | Deshpande      |         |          | installation of  |
|            |                |         |          | the New Trigger  |
|            |                |         |          | Counter.         |
+------------+----------------+---------+----------+------------------+
|            | Auxillary      | 50%     | 100%     | Several years in |
|            | Systems and    |         |          | PHOBOS as RHIC   |
|            | Integration    |         |          | Liaison.         |
|            | Manager        |         |          | Responsible for  |
|            |                |         |          | day-to-day       |
|            | Robert Pak     |         |          | operations in    |
|            |                |         |          | PHOBOS.          |
+------------+----------------+---------+----------+------------------+
|            | Software       |         | 100%     | Oversee          |
|            |                |         |          | simulations,     |
|            | TBD            |         |          | reconstruction,  |
|            |                |         |          | DCA, efficiency  |
|            |                |         |          | calculations.    |
+------------+----------------+---------+----------+------------------+

### Specification of deliverables

Figure 53 shows the construction and organization chart for the VTX
project. The VTX is divided into subprojects, which themselves are
divided into tasks. The tasks closely relate to deliverables, which need
to be completed before the VTX construction project can be considered
complete. The proposed fiscal responsibility for each deliverable,
either RIKEN or DOE, is indicated in brackets. Expected institutional
involvement is listed together with the fiscal responsibilities in
Figure 53. The present and future involvement of individual institutions
is discussed in more detail in the next section.

Outer layer silicon strip detectors:

-   Silicon strip sensors designed and tested to specifications (RIKEN)

-   SVX4 readout cards (ROC\'s) developed and manufactured (DOE)

-   Strip sensors integrated with ROC\'s (RIKEN)

-   Pilot modules to readout ROC\'s from detector assembly (DOE)

-   Front-end modules (FEM\'s) to collect data from pilot modules (DOE)

-   Detector ladder, sensors-ROC\'s assemblies with pilot module mounted
    on readout bus (DOE)

-   Commissioning of strip detector ladders (DOE)

Inner layer silicon pixel detector:

-   Tested sensor assemblies which include one sensor and 4 readout
    chips (RIKEN)

-   Readout bus to read data from sensor assemblies manufactured and
    tested (RIKEN)

-   Two sensor ladders mounted on readout bus and tested (RIKEN)

-   Pilot card to readout pixel hybrids from one readout bus produced
    (RIKEN)

-   Half ladders, combining readout bus, two sensor ladders and pilot
    module assembled and tested (RIKEN)

-   Assembly and commissioning of half ladders to full ladders (RIKEN)

-   Front-end modules (FEM\'s) ready to collect data from pilot modules
    (DOE)

DAQ system

-   Data collection modules for pixel and strip detector manufactured
    and tested (DOE)

Auxiliary Systems and Integration

-   System support requirements specified, including heat loads, power
    distribution, mechanical tolerances and ground scheme (DOE)

-   Mechanical support structure designed and manufactured (DOE)

-   Ancillary systems operational, including power distribution and
    cooling system (DOE)

-   Strip and pixel detectors ladders mounted in mechanical support
    (DOE)

-   Full system tested in assembly laboratory (DOE)

-   Commissioning of full detector system (DOE)

-   VTX installed at final location in PHENIX experimental (DOE)

-   Full system test in PHENIX (DOE)

-   Integration into PHENIX DAQ system (DOE)

## 6.3 Manpower for Tasks {#manpower-for-tasks .unnumbered}

The following tables document which tasks people will work on in the VTX
project

[]{#__RefHeading___Toc66641838 .anchor}Table 9 Collaboration members
working on the inner-layer/pixel sub-task.

  --------------- -------------------- ---------------------------------------
                  People               Experience

  Inner Layer     Hiroaki Ohnishi      Leading RIKEN group at CERN testing and
  Manager         (RIKEN)              assembling pixel detector for NA60 and
                                       ALICE

  Pixel Readout   Johann Heuser        1992-1999: Development of pixel
  chips,          (RIKEN)              detectors, RD19 Collaboration, CERN.
  bump-bonding,                        1994-1999: Construction, Commissioning,
  hybrids                              Operation of the DELPHI pixel detector
                                       and DELPHI Silicon Tracker.Since 2001:
                                       Construction, Commissioning and
                                       Operation of the NA60 pixel detector.

  Pixel Pilot     Hiroyuki Kano(RIKEN) Last year at CERN with PILOT team,
  module                               several years developing ASICS

                  Jonathon Crandall    Masters student in EE
                  (ISU)                

  Pixel Bus       Atsushi Aketani      
                  (RIKEN)              
  --------------- -------------------- ---------------------------------------

[]{#__RefHeading___Toc66641839 .anchor}Table 10 Collaboration members
working on the outer/strip sub-task.

+----------+-------------------+---------------------------------------+
|          | People            | Experience                            |
+----------+-------------------+---------------------------------------+
| Outer    | Abhay Deshpande   | Several years experience in PHENIX,   |
| Layer    | (SBU)             | managed design and installation of    |
| Manager  |                   | New Trigger Counter.                  |
+----------+-------------------+---------------------------------------+
| Silicon  | Junji Tojo        | Led PHENIX strip R&D last two years.  |
| strip    | (RIKEN)           |                                       |
| sensors  |                   |                                       |
+----------+-------------------+---------------------------------------+
|          | Yuji Goto (RIKEN) | Convenor of PHENIX Si study group     |
|          |                   | 2000-2003                             |
+----------+-------------------+---------------------------------------+
|          | Zheng Li, Don     | Designed and fabricated several       |
|          | Elliott, Rolf     | similar sensors                       |
|          | Beuttenmuller BNL |                                       |
|          | ID                |                                       |
+----------+-------------------+---------------------------------------+
|          | Naohito Saito     |                                       |
|          | (Kyoto)           |                                       |
+----------+-------------------+---------------------------------------+
|          | Manabu Togawa     | Graduate student in physics           |
|          | (Kyoto)           |                                       |
+----------+-------------------+---------------------------------------+
| Silicon  | Vince Cianciolo   | Several years experience in PHENIX,   |
| strip    | (ORNL)            | managed design and installation of    |
| read-out |                   | FEE for PHENIX MUID                   |
+----------+-------------------+---------------------------------------+
|          | Paul Stankus      |                                       |
+----------+-------------------+---------------------------------------+
|          | Miljko Bobrek     | Several years experience designing    |
|          | (ORNL)            | analog, digital systems, including    |
|          |                   | PHENIX front-end electronics systems. |
+----------+-------------------+---------------------------------------+
|          | Kim               | As above                              |
|          | Castleberry ORNL  |                                       |
+----------+-------------------+---------------------------------------+
|          | Chuck Britton     | As above                              |
|          | ORNL              |                                       |
+----------+-------------------+---------------------------------------+
|          | Bill Bryan ORNL   | As above                              |
+----------+-------------------+---------------------------------------+
|          | Alan Wintenberg   | As above                              |
|          | ORNL              |                                       |
+----------+-------------------+---------------------------------------+
|          | Atsushi Taketani  |                                       |
|          | (RIKEN)           |                                       |
+----------+-------------------+---------------------------------------+
| Silicon  | Miljko Bobrek     | Several years experience designing    |
| strip    | (ORNL)            | analog, digital systems, including    |
| pilot    |                   | PHENIX front-end electronics systems. |
+----------+-------------------+---------------------------------------+
|          | Craig Ogilvie     |                                       |
|          | (ISU)             |                                       |
+----------+-------------------+---------------------------------------+
|          | Gary Sleege (ISU) | Several years experience designing    |
|          |                   | digital systems                       |
+----------+-------------------+---------------------------------------+
|          | John Lajoie (ISU) | Several years designing/implementing  |
|          |                   | PHENIX LVL1 boards and systems        |
+----------+-------------------+---------------------------------------+
|          | Steve Skutnik     | Masters student in Physics            |
|          | (ISU)             |                                       |
+----------+-------------------+---------------------------------------+
| Silicon  | Doug Fields (UNM) |                                       |
| strip    |                   |                                       |
| assembly |                   |                                       |
| testing  |                   |                                       |
+----------+-------------------+---------------------------------------+
|          | Rachid Nouicer    | construction, installation, and       |
|          |                   | commissioning of PHOBOS               |
|          | (BNL Chemistry)   |                                       |
+----------+-------------------+---------------------------------------+
|          | Hubert van Hecke  | From MVD: QA procedures for silicon   |
|          | (LANL)            | detector testing, Silicon strip and   |
|          |                   | pad detector assembly, readout        |
|          |                   | electronics etc                       |
+----------+-------------------+---------------------------------------+
|          | John Sullivan     | As above                              |
|          | (LANL)            |                                       |
+----------+-------------------+---------------------------------------+
|          | Jan Boissevain    | As above                              |
|          | (LANL)            |                                       |
+----------+-------------------+---------------------------------------+

[]{#__RefHeading___Toc66641840 .anchor}Table 11 Collaboration members
working on the auxiliary systems/integration sub-task.

+------------+----------------+---------------------------------------+
|            | People         | Experience                            |
+------------+----------------+---------------------------------------+
| Auxiliary  | Robert Pak     | Several years in PHOBOS as RHIC       |
| Systems    |                | Liason. Responsible for day-to-day    |
| and        | (BNL           | operations in PHOBOS.                 |
| I          | chemistry)     |                                       |
| ntegration |                |                                       |
| Manager    |                |                                       |
+------------+----------------+---------------------------------------+
| Mechanical | Dave Lee       | Leads mechanical design for VTX,      |
|            | (LANL)         | managed the design of the mechanical  |
|            |                | for the SSC/GEM silicon vertex        |
|            |                | tracker managed the R&D, design and   |
|            |                | construction of the PHENIX muon       |
|            |                | system detectors and mechanics        |
+------------+----------------+---------------------------------------+
| I          | C.L. Woody     | Several years integration experience  |
| ntegration | (BNL)          | PHENIX                                |
+------------+----------------+---------------------------------------+
|            | Walt Sondheim  | chief engineer on the Fermilab E789   |
|            | (LANL)         | silicon tracker, chief design and     |
|            |                | integration engineer for the PHENIX   |
|            |                | muon tracker                          |
+------------+----------------+---------------------------------------+

[]{#__RefHeading___Toc66641841 .anchor}Table 12 Collaboration members
working on the software sub-task.

+------------+----------------+---------------------------------------+
|            | People         | Experience                            |
+------------+----------------+---------------------------------------+
| Software   | TBD            | Oversee simulations, reconstruction,  |
| Manager    |                | DCA, efficiency calculations.         |
+------------+----------------+---------------------------------------+
|            | Sasha Lebedev  | Led PHENIX software effort for TEC    |
|            | (ISU)          |                                       |
+------------+----------------+---------------------------------------+
|            | Vladimir Rykov | Several years simulation experience,  |
|            | (RIKEN)        | STAR and PHENIX                       |
+------------+----------------+---------------------------------------+
|            | Hua Pei (ISU)  | PhD Physics, Track projections to vtx |
+------------+----------------+---------------------------------------+
|            | Jeff Mitchell  | Several years experience with PHENIX  |
|            | (BNL)          |                                       |
+------------+----------------+---------------------------------------+
|            | Peter          | Several years experience with PHOBOS  |
|            | Steinberg      |                                       |
|            |                |                                       |
|            | (BNL           |                                       |
|            | Chemistry)     |                                       |
+------------+----------------+---------------------------------------+
|            | Pat McGaughey  | designed the E789 silicon tracker,    |
|            | (LANL)         | Several years experience with PHENIX  |
+------------+----------------+---------------------------------------+

[]{#__RefHeading___Toc66641842 .anchor}Table 13 Collaboration members
working on the DAQ sub-task.

  ------------- ----------------- ----------------------------------------
                People            Experience

  Data          J.S. Haggerty     Responsible for DAQ PHENIX
  acquisition   (BNL)             
  and                             
  interfaces                      

                Andrei Sukhanov   (real-time programming, firmware
                (BNL Chemistry)   programming, triggering, electronics
                                  etc.).

                Axel Drees (SBU)  Led similar effort for PHENIX drift
                                  chamber FEM'S

  FEM           C. Pancake (SBU)  Designed PHENIX drift chamber FEM's
  ------------- ----------------- ----------------------------------------

## 6.4 Institutional involvement {#institutional-involvement .unnumbered}

Currently 13 institutions with a total of 66 collaborators are involved
in the VTX project. The different institutions bring in diverse research
background, physics interests and expertise, which form a broad base to
carry out the proposed project. All groups have taken on specific
responsibilities and will actively participate in the VTX project.
Matching their expertise these group will be involved in construction,
installation, commissioning, operation, and data analysis. Formal
commitments of the involved institutions will be specified in MoU\'s. At
this early stage of the project naturally some groups have been actively
involved and launched R&D through institutional contributions while
others have joined the project only recently. In the following we will
briefly discuss the different groups, their expertise and their
potential involvement. Florida State University and the RIKEN BNL
Research Center have made major contributions to this proposal and will
specify their specific responsibilities in the future. The BNL
Instrumentation Division, KEK, and Niigata join the VTX project because
of their interest in the technological development, but are not members
of the PHENIX collaboration.

### Brookhaven National Laboratory, Chemistry Department (BNL CHEM)

Mark Baker and his group bring in broad experience with silicon detector
technology. In addition to management and physics experience, each group
member brings specific technical skills that will be important for the
successful construction, installation, commissioning and operation of a
silicon detector in the RHIC environment.\
Rachid Nouicer is one of the two primary silicon experts active on
PHOBOS, having participated in the construction, installation, and
commissioning of the detector. He is currently responsible for the
multiplicity barrel, rings, and vertex silicon detectors within PHOBOS
and he led the successful effort to replace damaged ring modules by
building new ones from scratch. Robert Pak is responsible for the
silicon cooling and dry air systems, for the radiation-monitoring
chipmunks, and also the beryllium beam pipe. Andrei Sukhanov is an
expert in data acquisition (real-time programming, firmware programming,
triggering, electronics etc.). Finally, Peter Steinberg played a major
role in the design, development, and implementation in the silicon
detector signal processing algorithms and software chain.

At present the focus of the group is on operations and analysis of the
PHOBOS experiment, but over the next three years, their hardware effort
will increasingly focus on the VTX project. The group will actively
participate in assembly, integration and testing of the strip detector
assemblies and of pixel and strip detector ladders mounted in the
mechanical support. In the longer run the group foresees playing a
leading role in the commissioning and operation of the VTX system in
PHENIX.

### Brookhaven National Laboratory, Instrumentation Division (BNL ID)

BNL\'s Instrumentation Division\'s Silicon Detector Development and
Processing Laboratory (SDDPL) will be involved in the development of
silicon strip detectors for PHENIX Upgrades. The activity will include
detector simulation, design, and processing of prototype detectors.
SDDPL will also be involved in laser scan tests of those prototypes,
these tests will be carried out in close collaboration with the RIKEN
Institute and RIKEN-BNL Research Center. Concerning the mass production
of detectors, SDDPL will develop the detector processing receipt,
produce the final mask set, and help transfer the processing technology
and mask set to a industrial manufacturer. Zheng Li, the group leader of
SDDL, Don Elliott, the Processing Engineer, and Rolf Beuttenmuller, the
Senior Processing Technician will be involved in these activities.

### Brookhaven National Laboratory, Physics Department (BNL PHY)

The PHENIX Group from the BNL Physics Department provides infrastructure
and technical support as part of Systems Engineering and Integration
(SE&I) for the entire PHENIX experiment. It has a staff of mechanical
and electrical engineers and a group of experienced technicians who are
intimately familiar with the detector, and work closely with the BNL
Collider-Accelerator Department for operations and any modifications to
its present design. They designed much of the infrastructure for the
baseline detector, including racks, cable trays, electrical power,
cooling, access, safety systems and numerous other services, and carried
out the installation of all of the present subsystem detectors. This
group will now be closely involved with the design of the infrastructure
and support for the silicon vertex detector, and with its installation
into PHENIX.

The BNL PHENIX group also has primary responsibility for a number of
major subsystems. These include Electronics Facilities and
Infrastructure (EF&I), Online Computing Systems (ONCS) and Offline
Computing. These groups will participate in the electronic integration
and readout of the silicon detector into the PHENIX data acquisition
system, and will be involved with track reconstruction and offline data
analysis.

### Iowa State University (ISU)

As DOE project manager, Craig Ogilvie plays a leading role in the
management of the VTX project. Over the past two years Ogilvie\'s
leadership role in the PHENIX Silicon Vertex Tracker working group was
essential to bring the project to the proposal stage. In addition, the
Iowa State group has been designing a parallel readout for the pixel
detectors that will work within PHENIX's readout time and replaces the
custom designed sequential readout ASIC\'s on the ALICE pixel detector
pilot module. The new parallel readout is implemented in radiation hard
FPGA\'s. The first design of the pixel pilot with parallel readout and
zero-suppression is completed and testing is underway. A MOU is being
negotiated with CERN to be able to include the control code into the new
Pilot. The FPGA design effort is led by Prof Garry Tuttle of the
Electrical Engineering Department and Professors John Lajoie and John
Hill. Gary has extensive experience with the design of digital and
analog systems and Prof. John Lajoie has considerable expertise in fast
digital logic from his prior work on the LVL1 detector in PHENIX. This
work will form the master's theses of two students, Jonathon Crandall in
Electrical Engineering and Steve Skutnik of the Physics Department.
Senior technician Gary Sleege and Harold Skank will help in the final
stages of the design and testing of the pixel pilots. The ISU group will
also work with ORNL on the design of the pilot for the strip layers. In
addition ISU graduate students will be available to help in various
assembly tasks for the VTX project as construction progresses.

### Kyoto University (Kyoto)

Naohito Saito together with Manabu Togawa is involved in the R&D effort
focused on the silicon strip sensors. Especially the beam test at KEK-PS
together with the RIKEN group provided crucial information on the
further development of the of the sensor prototype. The group will
participate further for the evaluation of the sensors. In addition the
group actively participates in the development of analysis techniques
and physics simulations to establish the design of the silicon strip
detectors. The advantage of VTX detector especially in photon-jet
production has been clearly demonstrated in the PYTHIA based
simulations. Such efforts will be continued to further optimize the
physics analysis strategy.

### Los Alamos National Laboratory (LANL)

The Los Alamos group has established three major initiatives for the VTX
upgrade in conjunction with our interest in pursuing new physics with
the muon arms. (A) We have worked with the mechanical design group of
the ATLAS silicon tracker, HYTEC, Inc, to develop a concept for the
mechanical structures for the integrated (barrel and end-cap) design of
the fully completed vertex tracker. Dave Lee, Walt Sondheim, and other
LANL members will continue to lead the effort to bring the concept to a
fully engineered mechanical design and to work closely with other
members of the VTX upgrade group and BNL to ensure effective integration
of the detector into PHENIX. (B) LANL group has also established
collaboration with the FNAL electronics group headed by Ray Yarema to
modify an existing chip design to read out mini-strips of the end-cap
extension. Gerd Kunde will continue that coordination responsibility
since it is vital to the end-cap effort. (C) An ongoing simulation
effort will be very important to these efforts and Pat McGaughey, Hubert
van Hecke, and other members of the LANL team will pursue these
activities.

The LANL group has extensive experience with silicon detectors
including, 1) a measurement of the of the *B* production cross section
and charm production nuclear dependence with a silicon vertex detector,
E789, at FNAL using electronics developed by Ray Yarema, 2) implementing
the SVXH readout chip for the L3 micro-vertex detector at CERN, 3)
extensive prototyping and testing in conjunction with the mechanical and
electronic designs for the GEM/SSC silicon micro-vertex detector, and
management responsibility for GEM; and 4) similar responsibilities for
the MVD. Over the next 3 years the LANL group will gradually reach a
level of effort equivalent to 3 FTE's per year to be devoted to the VTX
upgrade.

### University of New Mexico, Albuquerque (UNM)

The University of New Mexico medium energy physics group can contribute
in several areas of development for the silicon tracker including
simulations, sensor testing, hardware design, and fabrication. The
Nuclear and Particle physics groups at UNM have a long history of
silicon development, including a testing facility currently being used
for the ATLAS sensors and managed by technical staff member Martin
Hoeferkamp, and an extensive simulation and hardware development program
for the CDFII silicon vertex detector by the group of Prof. Michael
Gold. Profs. Douglas Fields and Bernd Bassalleck have experience with
smaller scale silicon projects at BNL and elsewhere, and have been
deeply involved in the design of the PHENIX Muon Tracking System in
collaboration with LANL and HYTEC, Inc. Our desire is to build upon this
local expertise and to help with the development of a quality assurance
program for the strip sensors, local testing of sensors, R&D for
hardware (experience in regulated power supplies, kapton cable design,
etc.), and simulation efforts. We have already become involved in the
simulation geometry development through the efforts of one of our
graduate students Michael Malik. In addition, we plan to hire two
additional postdocs, one of which would be resident at BNL.

### Oak Ridge National Laboratory (ORNL)

The Oak Ridge group consists of physicists and electrical engineers. The
group (Vince Cianciolo, Ken Read, Paul Stankus, Terry Awes, Glenn Young,
Chuck Britton, Bill Bryan, Alan Wintenberg and Miljko Bobrek) recently
secured internal funding dedicated to developing the system-level
architecture for the electronic readout of the outer barrel (strip
layers) using the SVX4 chip, and to test the compatibility of the SVX4
chip with the PHENIX architecture and with the proposed strip-pixel
sensors.

The ORNL group has extensive experience with design, construction and
commissioning of PHENIX front-end electronics systems and associated
ASICs. We anticipate leading the design, prototyping and fabrication
efforts for the various pieces of the readout electronics for the outer
barrels and collaborating with RIKEN and BNL groups in testing the
production components and integrating the full detector into PHENIX.

### RIKEN Institute (RIKEN)

The RIKEN group, lead by Hideto Enyo, has a key role in the VTX project.
Yasuyuki Akiba leads the VTX project and represents it in the PHENIX
detector council. Akiba previously lead design and construction of
PHENIX RICH detector, and he brings in ample experience from the RICH
construction. As leader of the RICH project he has gained experience in
all aspects of large scale construction projects and in particular also
in coordinating a close collaboration of US and Japanese institutions.

Two years ago RIKEN has taken the lead in a broad R&D effort to
establish silicon vertex detector technologies suitable for PHENIX.
RIKEN has started collaboration with the ALICE pixel group. At present
three members of the RIKEN group are at CERN working with ALICE to help
finalize the detector development and test the first generation of
detectors in the NA60 experiment, which is currently taken physics data
with a multi-layer silicon pixel hybrid telescope. Johann Heuser, and
Hiroaki Ohnishi have worked for many years developing pixel detectors at
CERN as members of the NA60 pixel team also working with ALICE. Johann
commissioned a pixel detector system for the DELPHI experiment before he
joined the RIKEN Institute. Hiroyuki Kano, who is also at CERN, is
working with ALICE to adapt the ALICE pixel pilot to the PHENIX
requirements.

RIKEN has also initiated R&D with the BNL Instrumentation Division to
develop novel silicon strip detectors. The effort includes R&D together
with ORNL to develop suitable readout electronics based on the SVX4
readout chip developed at FANL. Yuji Goto, Junji Tojo, and Atsushi
Taketani are participating in this endeavor.

In addition, the RIKEN group has engaged in Monte Carlo simulations to
establish basic performance of the VTX detector and in the development
of analysis strategies and software.

### Stony Brook University, Physics Department (SBU)

Axel Drees together with a group of students has launched an effort to
adapt an FEM, originally built for the PHENIX drift chamber, to readout
the ALICE silicon pixel hybrids. In collaboration with NA60 the group is
gaining the necessary experience with the silicon pixel detectors. The
setup will serve as test sight for the PHENIX silicon pixel detectors.
Eventually, the effort will lead towards a new FEM design customized to
collect data from both the he pixel and strip assemblies. The design,
construction and commissioning of the FEM\'s will be carried out with
the help of the electronics workshop of the Stony Brook Physics
Department, lead by C. Pancake, the engineer who spearheaded the
development of the PHENIX drift chamber FEM\'s.

Abhay Deshpande has recently joined SBU hand is leading the Si strip
sub-task. He and post-docs, students in the group will take on major
responsibilities for testing of individual components, assembly,
commissioning of the VTX detector. The clean room facilities at Stony
Brook used for the PHENIX drift chamber assembly can be upgraded with
moderate effort to serve as basis for the VTX assembly.

## 6.5 Foreign contributions {#foreign-contributions .unnumbered}

The VTX project is funded in part by the RIKEN Institute. The tasks for
which the RIKEN Institute has taken fiscal responsibilities are
identified in the project chart (Figure 53) and are given in more detail
below:

Outer layer silicon strip detectors:

-   Silicon strip sensors designed and tested to specifications (RIKEN)

-   Strip sensors integrated with ROC\'s (RIKEN)

Inner layer silicon pixel detector:

-   Tested sensor ladders which include one sensor and 4 readout chips
    (RIKEN)

-   Readout bus to read data from sensor ladders manufactured and tested
    (RIKEN)

-   Two sensor ladders mounted on readout bus and tested (RIKEN)

-   Pilot card to readout pixel hybrids from one readout bus produced
    (RIKEN)

-   Half ladders, combining readout bus, two sensor ladders and pilot
    module assembled and tested (RIKEN)

-   Assembly and commissioning of half ladders to full ladders (RIKEN)

To enhance the expertise to carry out the work RIKEN has initiated
several co-operations with the BNL Instrumentation Division on silicon
strip sensors and with the ALICE/CERN pixel group on the silicon pixel
detectors. For the pixel hybrid detectors a memorandum of understanding
between RIKEN and CERN is in place. The objective of the memorandum is
the delivery of silicon pixel hybrids developed for the ALICE experiment
at CERN to RIKEN.

# Budget and schedule

## 7.1 Total estimated cost (TEC) {#total-estimated-cost-tec .unnumbered}

The costs and schedule for the VTX project have been developed using
engineering estimates, vendor quotes and experience from the
construction of the silicon pixel detector for NA60 and ALICE. The
proposed project is based on a cost sharing between the DOE Office of
Nuclear Physics and the RIKEN Institute of Japan. Responsibilities for
specific deliverables have been discussed in the previous chapter. RIKEN
funding started in April 2003 and we expect that it will continue at a
level of approximately \$1M per year for the next three years. In
addition, RIKEN provides substantial manpower (equivalent to \~ \$1M)
through in house contributions. The total estimated costs for the
proposed DOE construction project is \$5.6 M including an average
contingency of 32%. We have implemented a work breakdown structure
(WBS), which is the basis for the following is a more details on the
cost estimate and schedule.

### Fiscal Responsibilities

Table 14 summarizes the mapping of the major construction tasks onto the
proposed fiscal responsibility as discussed in the previous section.
Completion of some of these tasks will require collaboration and
expertise from institutions funded through the DOE as well as from
foreign institutions. In order to proceed with the project in a timely
manner and to bring technologies ready as soon as possible, R&D and
prototype cycles for some of the major tasks have been developed based
on both DOE and RIKEN funding.

### Contingency Analysis

In order to estimate the necessary contingency we have taken the
following approach:

-   For all tasks that require design of components and the production
    of prototypes, contingency is taken to be 50% of the cost of one
    extra design plus prototype cycle.

-   For all testing, assembly, and installation tasks, we assume that
    the contingency is 50% of the costs.

-   For purchases based on vendor information, 25% of the cost is
    included as contingency.

-   For all other purchases, the contingency is 50% of the costs.

### Overhead Estimate

For the overhead we assume a 17.5% rate for MST at BNL as is the current
practice for capital construction project at BNL, e.g. US-ATLAS at BNL.
This 17.5% overhead is listed separately in our budget tables. Also
listed as overhead are 9% for funds that are transferred from BNL to
other institutions. The additional overhead charged by local institution
is not listed separately. However, these costs are included in the
budget tables. In particular, all manpower costs are fully burdened
costs, including all overheads.

### Budget

Table 15 summarizes the estimated costs for the VTX project and shows
the split between the two funding agencies. For those items for which we
seek funding through the DOE, a detailed cost-breakdown is given in
Table 16.

[]{#__RefHeading___Toc66641843 .anchor}Table 14 Map of construction
tasks and WBS numbers onto the proposed fiscal responsibilities.

  --------------- ---------------------------------- ---------- ----------
  WBS             Construction Task                  DOE        RIKEN

  ***1.1***       ***VTX***                                     

  **1.1.1**       **Strip Layers**                              

  1.1.1.1.        Strip ROC Card SVX4                X          

  1.1.1.2         Strip Sensor                                  X

  1.1.1.3         Strip FEM/Pilot                    X          

  1.1.1.4         Strip Systems Tests                           X

  1.1.1.5         Strip Assembly and test                       X

  1.1.1.6         Services, LV, Racks                X          

  **1.1.2**       **Pixel Layer**                               

  1.1.2.1         Pixel sensor                                  X

  1.1.2.2         Pixel Readout-chip                            X

  1.1.2.3         Pixel Hybrid                                  X

  1.1.2.4         Pixel Bus                                     X

  1.1.2.5         Pixel Pilot Module                            X

  1.1.2.6         Pixel FEM                          X          

  1.1.2.7         Pixel System tests                            X

  1.1.2.8         Pixel Assembly and test                       X

  1.1.2.9         Services LV, Racks                 X          

  ***1.2***       *DAQ*                                         

  **1.2.1**       **Strip DCM**                      X          

  **1.2.2**       **Pixel DCM**                      X          

  ***1.3***       ***Auxiliary Systems +                        
                  Integration***                                

  **1.3.1**       **Specifications**                 X          

  **1.3.2**       **Mechanical**                                

  1.3.2.1         Support                            X          

  1.3.2.2         Ladders                            X          

  **1.3.3**       **Infrastructure**                 X          

  **1.3.4**       **Safety**                         X          

  **1.3.5**       **Installation**                   X          
  --------------- ---------------------------------- ---------- ----------

[]{#__RefHeading___Toc66641844 .anchor}Table 15 Overview of the total
estimated cost for the VTX project

  --------- ------------------------------- ------------ ----------- -----------
  **WBS**   **Name**                        **DOE**      **RIKEN**   **Total**

                                                                      

  1.1.1     STRIP                           2,180,695    1,302,125   3,482,820

  1.1.2     PIXEL                           575,700      1,690,375   2,266,075

  1.2       DAQ                             441,450      0           441,450

  1.3       AUXCILARY SYSTEMS & INTEGRATION 2,360,013    67,500      2,427,513

  1         Total                           5,557,858    3,060,000   8,617,858
  --------- ------------------------------- ------------ ----------- -----------

[]{#__RefHeading___Toc66641845 .anchor}[Table 16 Cost breakdown for
tasks to be funded through the DOE. Tasks which do not show a cost
correspond to deliverables for which the RIKEN Institute will take
fiscal responsibility.]{.underline}

  ---------- --------------------- --------------- --------------- --------------- ------------- --------------- --------------- ---------------
  **WBS**    **Name**              **Fixed**       **Labor**       **DOE Const**   **BNL         **Contingency   **DOE           **Total DOE**
                                                                                   Overhead**    Percentage**    Contingency**   

  1.1.1      **STRIP**                                                                                                            

  1.1.1.1    Strip ROC Card SVX4   195,000         415,750         610,750         54,968        18.6            123,715         789,433

  1.1.1.2    Strip Sensor                                                                                                         

  1.1.1.3    Strip FEM/pilot       278,000         410,500         688,500         39,510        34.5            251,452         979,462

  1.1.1.4    Strip System tests    50,000          135,000         185,000         5,400         17.2            32,700          223,100

  1.1.1.5    Assembly and Testing  0               75,000          75,000          0             0.0             0               75,000
             of Strip                                                                                                            

  1.1.1.6    Services, LV, racks   56,000          10,000          66,000          9,800         50.0            37,900          113,700
             etc                                                                                                                 

             Totals:               579,000         1,046,250       1,625,250       109,678       25.7            445,767         2,180,695

                                                                                                                                  

  1.1.2      **PIXEL**                                                                                                            

  1.1.2.1    Pixel Sensors                                                                                                        

  1.1.2.2    Pixel ROC                                                                                                            

  1.1.2.3    Pixel Hybrid                                                                                                         

  1.1.2.4    Pixel Bus                                                                                                            

  1.1.2.5    Pixel Pilot Module                                                                                                   

  1.1.2.6    Pixel FEM             68,000          132,000         200,000         18,000        40.0            87,200          305,200

  1.1.2.7    Pixel Systems Test                    125,000         125,000                                                       125,000

  1.1.2.8    Pixel Assembly and                    75,000          75,000                                                        75,000
             Test                                                                                                                

  1.1.2.9    Services, LV, racks   40,000          0               40,000          7,000         50.0            23,500          70,500
             etc                                                                                                                 

             Totals:               108,000         332,000         440,000         25,000        23.8            110,700         575,700

                                                                                                                                  

  1.2        **DAQ**                                                                                                              

  1.2.1      Strip DCM             165,000         30,000          195,000         17,550        50.0            106,275         318,825

  1.2.2      Pixel DCM             45,000          30,000          75,000          6,750         50.0            40,875          122,625

             Totals:               210,000         60,000          270,000         24,300        50.0            147,150         441,450

                                                                                                                                  

  1.3        **AUXCILARY SYSTEMS &                                                                                                
             INTEGRATION**                                                                                                       

  1.3.1      Specifications        0               67,500          67,500          0             50.0            33,750          101,250

  1.3.2      Mechanical Structure  487,000         363,000         850,000         76,500        25.0            231,625         1,158,125

  1.3.3      Infrastructure        90,000          550,000         640,000         15,750        29.9            196,075         851,825

  1.3.4      Environmental Safety  0               50,000          50,000          0             50.0            25,000          75,000
             & Compliance                                                                                                        

  1.3.5      Installation          5,000           110,000         115,000         875           50.0            57,938          173,813

             Totals:               582,000         1,140,500       1,722,500       93,125        30.0            544,388         2,360,013

                                                                                                                                  

  **5.11**   **Totals:**           **1,479,000**   **2,578,750**   **4,057,750**   **252,103**   29.0            **1,248,005**   **5,557,858**
  ---------- --------------------- --------------- --------------- --------------- ------------- --------------- --------------- ---------------

## 7.2 Schedule

The following plots summarize the construction schedule to complete the
VTX detector upgrade for PHENIX. The overall schedule is shown in Figure
54. It assumes start of the DOE construction project in FY05. The
subsequent plots, Figure 55 to Figure 57, show the detailed schedule for
each major WBS element. The schedule implies that construction dollars
from RIKEN are available 2003 through 2005 and that the DOE construction
funds become available in FY05.

Figure 58 gives the funding profile for the DOE project. In this
schedule the inner pixel layer and part of the strip layers will be
installed in summer 2006 and the full VTX detector will be completed in
summer 2007.

![](media/image69.png){width="5.747222222222222in"
height="2.2291666666666665in"}

[]{#__RefHeading___Toc66641825 .anchor}Figure 54 The overall schedule
for the VTX Project.

![](media/image70.png){width="5.747222222222222in"
height="3.3673611111111112in"}

[]{#__RefHeading___Toc66641826 .anchor}Figure 55 The schedule for the
strip layers.

![](media/image71.png){width="5.999305555555556in"
height="3.8743055555555554in"}

[]{#__RefHeading___Toc66641827 .anchor}Figure 56 The schedule for the
pixel layers

![](media/image72.png){width="5.747222222222222in"
height="5.618055555555555in"}

[]{#__RefHeading___Toc66641828 .anchor}Figure 57 The schedule for the
auxiliary systems and infrastructure

![](media/image73.wmf)

[]{#__RefHeading___Toc66641829 .anchor}Figure 58 Budget profile for the
VTX project

# 

# Appendix A ENDCAP Extension

## Introduction

This section outlines our plans to propose and construct a Silicon
Endcap Vertex Detector for PHENIX. The Endcap vertex detector
complements the barrel vertex detector by providing larger Bjorken-*x*
coverage, higher total rates and greater reach in transverse momentum.
In the following sections, we outline the physics case, specify the
requirements, list possible technical options, and define the needed
R&D. There are three broad physics topics that are accessible using an
Endcap Si vertex detector.

-   A large increase in the range of *x* over which we can extract the
    gluon spin structure function in protons with measurements of open
    charm and beauty in polarized *p+p* reactions.

-   Robust measurement of the shadowing of the gluon structure function
    in nuclei with measurements of open charm and beauty in *p+A*
    reactions.

-   Probing the early, highest energy-density phase of the matter formed
    in a heavy-ion reaction using the production of heavy flavor. There
    are several opportunities:

    -   Measuring the high-*p*~T~ spectra of open charm and beauty above
        4 GeV/c. The energy-loss of high-pt heavy-quarks is predicted to
        be less than for lighter-quarks.

    -   Measuring the yields of both open-charm and beauty in multiple
        channels to firmly establish whether heavy-quarks are enhanced
        in the pre-equilibrium phase.

    -   Using the open charm yield to form the ratio J//(open charm) and
        hence to quantify the suppression of J/

    -   Identification of upsilon states at rapidity near zero.

Our physics goals require that we measure charm and beauty mesons over a
broad range of rapidity and transverse momentum. The proposed Endcap
vertex detector achieves this by measuring displaced tracks that are
matched to the muon arms of PHENIX. A broad *p*~T~ and rapidity range is
achieved by using different decay channels to reach different parts of
phase space. The planned upgrade will operate well at 40× design
luminosity and many of the measurements need the higher luminosity, e.g.
upsilon and open beauty.

The proposed detector (VTX) is shown schematically in Figure 1, where
there are three distinct parts, a central barrel and two endcaps. The
Endcap silicon detectors are designed to provide coverage in the angular
acceptance of the forward Muon Arms. They cover 1.2 \< \|\| \<2.7 and
the almost full azimuth angle with a resolution of \~150 m. Each endcap
comprises four octagonal "lampshades" populated with Si mini-strip
detectors.

![](media/image74.jpeg){width="4.331944444444445in" height="2.26875in"}

Figure 1. Cross-section view of the proposed vertex detector.

![](media/image75.png){width="3.3694444444444445in"
height="2.5208333333333335in"}

Figure 2. A schematic cut-away mechanical drawing of the proposed vertex
detector (from Hytec).

A schematic mechanical drawing developed by HYTEC engineering is shown
in Figure 2. The proposed detector complements the existing muon arm
detectors and significantly enhances the muon physics program.

## A.1 Goals of the Endcap Upgrade

### A.1.1 Spin Structure of the Nucleon

PHENIX has the existing capability shown in Figure 3 as the blue lines.
However there are significant gaps in this *x*-range that will make it
difficult to fully address the spin-crisis. The proposed Si Endcap
detector extends the coverage to the lowest and highest *x*-values,
0.001 \< *x* \< 0.3, as well as providing significant regions where
multiple channels overlap. This overlap will provide vital cross-checks
that will improve the reliability of global fits to the spin structure
function.

![](media/image76.png){width="4.159027777777778in" height="3.4in"}

Figure 3. Expected x-range for different channels used to extract the
gluon spin structure function. The blue bars indicate PHENIX's existing
capability, green bars are for the Barrel upgrade, while the red bars
indicate the additional coverage provided by the proposed Endcap vertex
upgrade. The curves show various estimates of the expected gluon
polarization.

The Endcap vertex detector provides the following improvements in
x-range over a Barrel only detector. These have been estimated by
simulating *p+p* collisions with PYTHIA and requiring sufficient counts
in each exit channel to be able to make a reasonable measurement.

-   $c\overline{c}$production via gluon fusion. The x-range is extended
    considerably down to *x* = 0.001 using $D \rightarrow \mu X$.

-   $b\overline{b}$ production via gluon fusion. With the upgrade we can
    identify displaced J/ from $B \rightarrow \frac{J}{\Psi}$ decay.
    This provides coverage in x between 0.005 - 0.3. The selection of
    semi-leptonic decays $b\overline{b} \rightarrow e\mu X$ at high
    momentum is improved using displaced vertices. This extends the
    *x*~gluon~ coverage for these semi-leptonic decays to 0.01 - 0.3.
    Measurement of $B \rightarrow \mu X$ is also possible by placing a
    cut on the *p*~T~ of the muon.

.

### A.1.2 Exploration of Gluon Structure in Nuclei

The reach in *x*-range for the Si Endcap is indicated in Figure 4,
superimposed on calculations of the ratio of nuclear to nucleon gluon
structure function. The red bars indicate the additional coverage
provided by the Endcap vertex upgrade compared to the baseline of
PHENIX. The Endcap vertex upgrade provides extends the *x*-range from
the anti-shadowing region into the shadowing domain, which means we will
be able to establish the shape of the gluon structure function in
nuclei. The shadowing region is not accessible with the Barrel-only
upgrade. While the *x*-range for J/production also extends into the
shadowing range, final state effects, such as dissociation, complicate
the extraction of the gluon structure function. Open charm and beauty
measurements are unaffected by these final state effects.

![](media/image77.png){width="4.034722222222222in"
height="3.3833333333333333in"}

### A.1.3 Probes of Early, Highest Energy-Density Stage of Heavy-ion Reactions

Information from the Si Endcap concerning the yield and spectra of
heavy-flavor mesons is discussed in the following sub-sections. Of
critical importance, is the broad reach in rapidity and transverse
momentum made possible by the proposed Endcap upgrade.

### 

### Energy Loss of Heavy Quarks

Measuring the high-p~T~ (above 4 GeV/c) spectra of open charm and beauty
will provide a test of the various theoretical models of energy loss.
Since the cross section for these events is low, the large acceptance of
the Endcap vertex upgrade versus the Barrel is a distinct advantage.

### Open Charm and Beauty Enhancement

The Endcap vertex detector, combined with the muon spectrometers,
provides excellent rates of open charm and beauty detection. The Endcap
upgrade identifies and separates charm and beauty production with high
accuracy, even at low *p*~T.~

### J/ Suppression

To quantitatively understand suppression requires knowledge of the
initial production of $c\overline{c}$pairs. The effectiveness of a
deconfined medium in preventing the formation of J/ can be quantified
using the ratio J//(open charm) in the same acceptance as PHENIX
measures J/The Endcap upgrade provides for the detection of open charm
over about the same rapidity interval as for J/ decays to dimuons.

### Other Physics Topics

The Si Endcap vertex upgrade will help other physics programs in PHENIX
:

#### 

#### The J/ resolution in the muon arms will be improved using a vertex detector, from \~150 MeV down to \~100 MeV. This is important for separating the ' from the J/. The physics interpretation is cleaner for the ' than the J/ since it does not have such a large contribution from feeddown of the χ~c~ states. Figure 5 demonstrates the improved separation possible with the Si Endcap. 

#### The signal to background ratio for muon-pairs will be greatly improved by the removal of muons from long-lived pion and kaon decay. This is especially important for pairs with mass below the J/where the backgrounds are large in nucleus-nucleus collisions. 

#### 

![](media/image78.png){width="4.117361111111111in"
height="2.7729166666666667in"}

Figure 5 -- Mass spectra for the J/ and \', showing the substantial
improvement in separation expected with a vertex detector (yellow, 100
MeV resolution) compared to that without a vertex detector (black, 150
MeV resolution). The number of J/ and ' in this plot represents our
expectation for a \~25 pb^-1^ p-p run.

## A.2 Simulations and Required Performance for the Si Endcap Upgrade

The performance requirements for the Si Endcap detector are :

-   Ability to match tracks from a muon arm to hits in multiple layers
    of the Si detector.

    a.  Sufficient position accuracy so that the displacement resolution
        of the track with respect to the collision point is less than
        the c of charm and beauty decays, i.e. a resolution less than
        100m, preferably at the level of 30 - 50 m.

    b.  Good resolution in both r and z are required.

    c.  Sufficient segmentation to operate well in Au-Au and high
        luminosity p-p collisions.

For the simulations we have used two nominal thickness for each layer:
1% and 2% radiation length. This includes detector, readout and cooling
in a simplified one-volume effective layer. Our current concept will
have a radiation length close to 1% because we are implementing a design
that has incorporated a readout bus in the silicon chips and sensors and
we are able to thin the chips. We are striving to minimize this
thickness, in particular for the critical first disk.

The endcaps mini-strips vary in size from 50m by 2000m to 50m by 9000m
as the radius increases. This keeps the occupancy at or below 1.5%.

### A.2.1 Open Charm Measurement

> **Si Endcaps:** $D \rightarrow \mu X$**,**
> $D\overline{D} \rightarrow \mu\text{eX}$**,**
> $D\overline{D} \rightarrow \mu^{+}\mu^{-}X$

Each silicon endcap detector has four layers of pixel detectors, which
measure the trajectory of particles within the nominal rapidity
acceptance of the muon arms. The impact parameter of each track is
determined accurately along the Z (beam) direction. For each detected
muon, the impact parameter is used to eliminate muons that come from
pion and kaon decays. These long-lived decays are the primary source of
background muons.

Contrasted with these background muons are \"prompt\" single muons,
which come from more short-lived decays, e.g. open charm and beauty. For
transverse momenta below \~5 GeV/c the prompt muons are primarily from
semi-leptonic charm decay. Other processes that produce prompt muons,
such as J/or Drell-Yan decays to muon pairs, have much smaller
cross-sections times branching ratios. Muons from *B* decays become
important only at larger transverse momenta.

The PYTHIA event generator was used to simulate semi-leptonic charm
decays to muons. The total charm pair cross-section was set at 350 µb,
which is consistent with recent NLO theoretical calculations and with
the published PHENIX measurement at a somewhat lower energy. The decay
muons were tracked through the proposed silicon vertex detector and then
through the muon spectrometer using PISA.

The mean vertex of the detected muons from charm decay is 785m from the
interaction vertex. This is \~2.5 times larger than the proper decay
length of semi-leptonic charm decays (m), due to the Lorentz boost. The
impact parameter resolution for these muons ranges from 92 to 115 m,
depending on how many layers of silicon are transversed. By requiring
that the muon vertex is within 1cm of the collision point we remove many
of the muons from pion and kaon decay while retaining prompt muons from
charm and beauty.

Figure 6 shows a simulated muon *p*~T~ spectrum, including charm, beauty
and light quark decays, before the application of a vertex cut. The
background from light quark decays dominates the spectrum below 4 GeV/c.
The *p*~T~ distribution of muons that survive a 1 cm vertex cut is shown
in Figure 7. This vertex cut reduces the muon background from light
mesons by about an order of magnitude over what the muon arm alone can
achieve, making a charm measurement possible even at low *p*~T~. Note
that the removal of the muon background from pion and kaon decays could
be achieved with a detector with less spatial resolution. The resolution
requirement is driven by the physics program of measuring open beauty
(see next section).

![](media/image79.png){width="3.8916666666666666in" height="2.79375in"}

Figure 6. Single muon p~T~ distributions for charm, beauty and
backgrounds from low-mass meson decays, as expected for the 2003 d-Au
run. Note that the light-meson decays are above charm up to near 4
GeV/c. The black curve is for pion and kaon decays, green is charm and
red is beauty.

![](media/image80.jpeg){width="3.682638888888889in"
height="3.682638888888889in"}

To calculate the yield of charm, we assume a 650 µb D pair
cross-section, integrated *p-p* luminosity on tape of 50 pb^-1^,
acceptance time branching ratio of 0.0091 and two Si Endcaps. A total of
about 3.2 x 10^8^ semi-leptonic charm decays would be reconstructed.
This rate is before application of a vertex or impact parameter cut.
Even if a large prescale is required for single muon triggers, the yield
is still very large.

Since charm is produced in pairs, coincidence measurements of
opposite-sign lepton pairs may serve to further enhance the signal to
noise in *p-p* and *p-A* reactions. One could use vertex identified
muon-electron coincidences to obtain a clean charm pair signal in the
rapidity interval midway between the PHENIX central and muon arms.

### A.2.2 Open Beauty Measurement

B meson production, while much more rare than *D* production, is
somewhat simpler to measure. The challenge is the relatively low rate.
There seem to be at least two possibilities :

-   Since beauty mesons have a larger lifetime than charm mesons, it is
    possible to extract the beauty yield from the distribution of decay
    distances of single muons from semi-leptonic decays. At large
    transverse momentum beauty decays dominate the DCA distribution.

-   The decay channel *B* J/+X produces J/s that are displaced from the
    collision point.

**Si Endcaps:**
$B \rightarrow \frac{J}{\psi} \rightarrow \mu^{+}\mu^{-}$**,**
$B \rightarrow \mu X$

Applying a vertex cut on each reconstructed J/ has been used
successfully to identify B-production in experiments at lower
energies[^38]. Since the B cross-section is larger at RHIC energies, the
measurement should be easier. As the average p~T~ of J/ from beauty
decays is larger than for prompt J/, a p~T~ cut could also be used to
enrich the beauty sample.

Pythia was used to simulate
$B \rightarrow \frac{J}{\psi} \rightarrow \mu^{+}\mu^{-}$ decays. The
resulting muons are tracked through the silicon and muon spectrometers
using PISA. The muons have an impact resolution of \~55 m, significantly
better than muons from D decays, due to their larger average momentum.
The pair z-vertex resolution is \~133 m, while the mean decay length is
\~1.1mm. With a downstream pair z-vertex cut of 1 mm, 39% of the B
decays are retained, while the prompt J/ are attenuated by a factor of
2x10^-4^. Figure 8 shows the reconstructed Z-vertex distribution for the
J/ from B decays as well as prompt J/.

![](media/image81.jpeg){width="3.651388888888889in"
height="3.5340277777777778in"}

We have assumed a total B cross-section of 2 microbarns and 4 microbarns
for J/production. The branching ratio of 1.2% for
$B \rightarrow \frac{J}{\Psi}$ has been previously measured. The total
acceptance \* BR for these events using two Si Endcaps is \~
4.0\*10^-5^. Assuming an integrated luminosity to tape of 50 pb^-1^,
about 1900 $B \rightarrow \frac{J}{\Psi}$ events would be reconstructed
after the application of a 1 mm vertex cut. For $B \rightarrow \mu X$,
the acceptance \* BR is \~ 0.0087. The corresponding yield is \~780,000
reconstructed events. Thus, an excellent *B* measurement is possible.

### A.2.3 Trigger Plans

We plan to use the level 1 single and di-muon triggers as the main
physics trigger for the Si Endcaps. Higher level triggers could be a
level 2 displaced track trigger, possibly similar to the trigger used by
CDF and E789. Both CDF and E789 implemented the trigger in hardware to
optimize it for speed. For PHENIX this could be ported to level 2. The
algorithm for the Si Endcaps / muon spectrometers would be very similar
to that done previously by E789.

The E789 algorithm functions in three steps (translated into PHENIX
language); 1) Muon tracks are found from stubs in the Muon ID and Muon
Tracker. The momentum and angle of each track are determined. 2) These
tracks are then matched to hits in the Si Endcap using a pre-computed
lookup table. 3) Si hits within the matching window are formed into a Si
track stub. The stub is then fitted with a straight line to determine
the momentum, angle and impact parameter of the track.

These events would then be passed to the level 2 triggers of displaced
vertexes and/or high-momentum tracks. For pair triggers, tracks could be
combined and fitted to determine a pair vertex.

###  A.2.4 Si Endcap Event Rates

The event yields in the previous sections are summarized below. They
assume an integrated p-p luminosity on tape (for Run 8) of 50 pb^-1^.
Yields from a comparable Au-Au run would be about a factor of 3X lower.
The yields for semileptonic heavy quark decays are about an order of
magnitude larger than for the Si Barrel, due to the larger acceptance of
the Si Endcap. The B decay rates could benefit from the increased
luminosity in the RHIC II proposal.

  ------------------------------------------------------------- -----------------------------------
  Observable                                                    Counts per RHIC p-p Run 8

  $$D \rightarrow \mu X$$                                       3.2 x 10^8^

  $$B \rightarrow \mu X$$                                       780k

  $B \rightarrow \frac{J}{\Psi X} \rightarrow \mu^{+}\mu^{-}$   1900
  ------------------------------------------------------------- -----------------------------------

### A.2.5 Matching to Muon Spectrometers 

Track matching between the Si Endcaps and the Muon Spectrometers was
studied by using hijing Au-Au central collisions in a PISA simulation. A
muon track was embedded in a hijing event. The muon track was found in
station 1 from the muon tracker by demanding that the muon reached the
middle of the MUID, i.e. the muon energy was \> 2.5 GeV. The
distribution of the muon hits in station 1 was found to be +- 2 cm from
the projection of the Si Endcap track, due to multiple scattering in the
central magnet steel. No other track in the tracker was found to be in a
+- 2cm cut around the muon hit in station 1. We then looked for all
tracks in the Si Endcaps that had their projection fall into the 2 cm
cut about the muon track. In addition to the muon, typically 3 other
tracks fell into this cut. Of these candidate tracks all except the muon
came from the primary interaction vertex. The background would be the
fraction of primary tracks that fall beyond a 1 mm cut.

### A.2.6 Integration with PHENIX

The proposed Endcap vertex detector matches and extends the capability
of the existing muon spectrometer arms. In addition a TPC is being
proposed to sit outside the vertex detector. The Detector Advisory
Committee recommended studies exploring the impact of the VTX on the TPC
with the possibility of standalone running for either detector. Because
the Endcaps are outside of the acceptance of the HBD/TPC we believe that
both detectors can operate simultaneously.

## A.3 Technical Aspects of the Proposed Endcap Vertex Detector

### A.3.1 Silicon Readout Chip --PHX

FNAL Electrical Engineering Department, ASIC development group (Group
leader, Ray Yarema) has designed the FPIX2 chip, a low-noise
programmable Si pixel readout chip for the planned BTeV experiment. The
chip is an advanced mixed analog/digital DC-coupled design optimized for
a detector with 50 m by 400 m pixels. The device has very low noise (60
electrons RMS) and high-speed readout, including the ability to
interface to a level 1 type trigger. Approximately 3000 FPIX2 chips have
been produced in an engineering run, with a high yield of fully
functional devices. Test results are very encouraging, with the
prototypes demonstrating excellent performance and minimal cross-talk.
Only minor design tweaks are needed before a production run of the
devices could be made.

The electrical design of the FPIX2 chip is similar to that needed for
the Si Endcap pixels. The main change required is to adapt the physical
chip geometry to accommodate the Endcap sensors larger mini-strips.
These modifications are not very difficult, with an estimate of 2
man-years. Yarema has offered the services of his engineers and
facilities to perform this work. They have already completed a
conceptual layout of the modified PHX readout chip, which is shown in
Figure 9. This elegant design has the readout bus structure integrated
into the chip itself, simplifying the sensor-readout assembly process.
The PHX chip will be bump-bonded to the sensor, with 200 m bump spacing.
This relatively large spacing was chosen to ensure high yields during
the assembly process. Yarema's team have also simulated the FPIX2
response with input capacitances corresponding to our larger mini-strips
and found it to be acceptable.

The schedule and R&D budget for the PHX chip development are given in
section 6.4 below. These were provided to us by Ray Yarema.
Approximately two years are need to complete all of R&D related to the
PHX chip.

### A.3.2 Silicon Ministrip Sensors

We plan on using existing technology for the silicon sensor. Pixel
Sensor technology from the either the ALICE, ATLAS or CMS efforts will
have the pixel layout (masks) modified to match the longer mini-strips
that we need. Developing the masks for this effort will be done in
concert with the vendors of the sensors. Lengthy and costly R&D for the
sensors is not necessary.

Three different silicon sensors of trapezoidal shape are used to tile
the active areas of the Si Endcap, as shown in Figure 10. Also shown is
the arrangement of the readout chips on each of the sensors. The largest
sensor is 79 mm high and 27 mm wide at its large end. Six PHX chips are
used to readout the 3072 mini-strips. The smaller sensors contain 2560
and 1536 strips.

![](media/image82.png){width="1.15625in" height="3.51875in"}

Figure 9: Conceptual layout of the PHX pixel readout chip. The left side
graphic depicts the general layout of the chip. Green is the area for
bonding, blue the programming interface, red the discriminator, orange
the pipeline and yellow the digital interface. The right side graphic
shows the bonding layout, the spacing is 200 micron. The signal and
power bus will be routed on the surface on the chip and bonded via the
bump bonds on the ends of the chip.

The Si Endcap detector layers are assembled as shown in Figures 11
through 13. First, the sensors are tiled on carbon panels that serve as
the support and cooling structure for each of the sector assemblies
(Figure 11). Next, 24 sectors are joined to form each of the four
z-Stations (Figure 12). Finally, the four z-Stations are assembled in
each Si Endcap detector (Figure 13). Each Endcap contains approximately
two million strips.

![](media/image83.jpeg){width="1.3493055555555555in"
height="3.435416666666667in"}![](media/image84.jpeg){width="1.8847222222222222in"
height="3.6840277777777777in"}![](media/image85.jpeg){width="1.7708333333333333in"
height="3.348611111111111in"}

Figure 10: Three silicon detectors will be used. The largest will have 6
chips reading out 3072 strips, the intermediate silicon will have 5
chips reading out 2560 strips and the smallest silicon is half the size
of the largest with 3 chips reading out 1536 strips. (All dimensions are
in millimeter)

![](media/image86.png){width="1.645138888888889in"
height="3.5541666666666667in"}

Figure 11: A sector assembly will have 24 carbon panels (one shown here
in brown) in azimuth, each of them carrying 4 silicon detectors (blue),
two in the front and two in the back. They overlap on the edges by a few
millimeters to avoid dead areas. The bus on a silicon assembly is routed
on the chips as described earlier, the connection of the inner silicon
detectors is realized via a kapton bus (golden).

![](media/image89.png){width="6.0in" height="3.3666666666666667in"}

Figure 12: Each station carries 96 silicon detectors. The stations are
placed at \~20, 26, 32 and 38 cm from the interaction point.

![](media/image90.png){width="4.189583333333333in"
height="3.3305555555555557in"}

Figure 13: Each endcap will have 4 stations of silicon detectors. The
inner station has a reduced size in order to not interfere with the HBD
acceptance.

### A.3.3 Silicon Ministrip Control Chip

The Control Chip serves as a receiver for the PHX chip digital output
and is located at the outer edge of each sector. It formats the data to
be compatible with the PHENIX DCMs, converts the data into serial form
and drives a 2.5 gigabit/sec fiber. The other end of the fiber connects
to the DCM in the counting house. It is simpler than the PILOT chip used
to interface the Si barrel, as it does not need to combine separate data
streams to meet PHENIX's DAQ speed requirements. (The PHX chip is
already fast enough for PHENIX). We envision that the Control Chip would
consist of an FPGA plus a laser diode and driver. The University of
Heidelberg has expressed interest in developing the Control Chip with
us.

### A.3.4 Mechanical Structure and Cooling

The mechanical structures and cooling are part of the integrated design
discussed in Chapter 4. The majority of the support structure will be
designed as part of the barrel effort and remaining issues concerning
ladders and cooling specific to the endcaps will be discussed here.

### A.3.5 Endcap Ladder Structure

The forward regions consist of 4 conical arrays of ladder modules tilted
from the normal to the beam pipe by 22 deg. Conceptually, we have chosen
a flat octagonal panel structure with sensors and electronics mounted on
either side of the panel so that we can achieve hermetic coverage.
Figure 14 shows this arrangement on the left and an octagon panel
structure on the right.

![](media/image91.jpeg){width="2.8055555555555554in"
height="2.502083333333333in"}
![](media/image92.jpeg){width="2.2118055555555554in"
height="2.7527777777777778in"}

##  

Figure 14. 3D model of octagonal disk like structures for the endcap
ministrips. Cooling tubes are shown to demonstrate both the number and
routing. The octagon panel structure is on the right with the cooling
channel shown. A heat load of 0.1 W/cm\*\*2 is assumed.

Each endcap has a total heat load of approximately 450W, or about 15W
per octant panel. In comparison to the barrel this is a very small heat
load and greatly simplifies the removal of the waste heat. The octant
panel structure consists of a composite sandwich of C_C facings on
either side of a carbon foam in which is embedded an aluminum cooling
tube( Figure 15). Thermal and gravity sag calculations were performed in
a manner similar to those discussed in chapter 4 and no serious
distortions were observed. For the case of 0 deg operation, more work is
necessary.

![](media/image93.png){width="3.9319444444444445in"
height="2.2104166666666667in"}

Figure 15. Illustration of an embedded cooling passage arrangement in
the composite sandwich used in the endcap thermal and static
calculations. The upper panel depicts a circular tube with supports and
the bottom panel shows a flattened tube which enhances heat transfer and
provides a thinner sandwich.

[A.3.6 Radiation Length]{.underline}

The thermal and static design studies produced a range of solutions for
the endcaps Figure 16 shows the radiation length estimate for different
cooling tube dimensions. The parameters used in the calculations are:

-   Al tube, 200 micron.

-   4 mm carbon foam separator.

-   Tube support 2 mm wider than tube diameter.

-   Sandwich facings of 400 micron.

![](media/image94.png){width="4.179861111111111in" height="2.28125in"}

Figure 16. Estimated normal radiation length for the endcap octant panel
for different tube diameters.

### 6.3.7 Endcap Analysis Summary

######## 

######## The conceptual design studies revealed the following:

######## Single phase cooling is well suited to the endcaps.

-   Two adjacent octant panels can be cooled in series thus reducing
    service connections.

-   2mm cooling tubes and panel thickness are adequate.

-   The radiation length of the octant panel exclusive of sensor and
    electronics is \~ 0.6 %.

The R&D issues consist of refining the calculations, designing
attachment points to the main support structure, and prototyping the
octant panels.

## A.4 R+D Schedule, Responsibilities and Budget

### A.4.1 Schedule

The R+D schedule for project 2 is shown below. Also shown is a
construction and installation schedule assuming funds are available now.
This will slide with funds availablity. The R+D is expected to begin in
early FY04 and be completed by late FY05.

![](media/image95.wmf)

### 

### A.4.2 Responsibilities

The LANL Group will work together with HYTEC inc. to develop the design
for the Endcap mechnical ladder and cooling. LANL has formed a
collaboration with FNAL to design, prototype and test the PHX readout
chip. LANL is forming collaboration with Ecole Poly-Technique and
Saclay, who will contribute to both the hardware and software efforts.

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