# Presentation: 693474

**STAR Inner Tracking Upgrades**
**with an emphasis on the Heavy Flavor Tracker**
**presented by**
**Jim Thomas**
**Lawrence Berkeley Laboratory**
**11 / 08 / 2006**

## The Light Quark Program at STAR is Compelling

- Its hot

- Its dense

- and it flows
- at the partonic scale

-  and , too!

- Spectra

**V****n**

- Jets & Rcp

- Now we can make these measurements in the charm sector

## Heavy Flavor Energy Loss ... RAA for Charm

**Heavy Flavor energy loss is uncertain**
**Gluon densities up to 3500 are insufficient to describe the data**
**~ 1000 from light quark data**
**Beauty dominates single electron spectra above  5 GeV and makes the model worse**

*M. Djordjevic, et. al. **nucl-th/0507019*

**Current energy loss mechanisms can only account for part of the strong suppression of R****AA**** for electrons**

**Notes:**
Figure 9: Non-photonic electron RAA in central Au+Au collisions from STAR (open-symbols, top 5%) and PHENIX (filled-symbols,  top 10%) from Refs. [58,59,60].  Theoretical predictions for charmed-hadron and charm and beauty-hadron decayed electrons are shown as blue- and yellow-bands, respectively. In these calculations, the initial gluon density was assumed to be unrealistically large: ~3500,  see Ref [63] .
Figure 9 shows RAA for non-photonic electrons[i],[ii],[iii] from STAR and PHENIX.  The data extend up to pT ~ 10 GeV/c.  The figure shows that the suppression factor for single electron spectra is in the range of 0.2-0.3 which is almost exactly the same as the suppression factor observed for charged hadrons and pions[iv],[v] (i.e. light quarks).  Using an unrealistically large initial gluon density of dNg/dy = 3500, Djordjevic, Gyulassy, Vogt and Wicks have done a pQCD calculation[vi], including gluon radiative energy-loss, which can barely reproduce the electron RAA (see the blue-line in Figure 9).  The model ignores the contributions from beauty-hadrons, and when beauty is added to the model, the resulting prediction for RAA cannot describe the data at all (see the yellow band in Figure 9 ); the model with beauty over-predicts the data by a factor of 2-3.   Note that for light-quark hadrons, like pions, a gluon density of ~1000 has been used to  reproduce the observed RAA[jt1].  These results raise a serious challenge to our understanding of both the mechanism for heavy-quark production and the mechanism for energy-loss in a hot and dense medium. In order to resolve these important issues, we have to do direct topological reconstruction of open charm.  It is experimentally and theoretically too difficult to make definite conclusions from the single-electron measurements due to the complications from the mixing of the electrons from D-meson decay and electrons from bottom hadron decay as well as the smearing of the decay kinematics. 

## Flow: Constituent Quark Number Scaling

- In the recombination regime, meson and baryon v2 can be obtained from the quark v2 :

**Does it work in the Charm Sector? A strong test of the theory**

## Elliptic Flow with Charm

- M. Kaneta (PHENIX), J. Phys. G: Nucl. Part. Phys. 30, S1217 (2004).

**D  ********  e +X**
**	****Single electron spectra from PHENIX show hints of elliptic flow**
**The HFT will cut out  large photonic backgrounds: ***** ***
****** ******** ****e+e-**
**	****and reduce other  large statistical and systematic uncertainties**
**STAR can make this measurement with      50 M Au+Au events in the HFT **
**Smoking gun for thermalization at RHIC!**

**Better if we can do direct topological identification of Charm**

**Notes:**
Figure 7:  Non-photonic electron elliptic flow at RHIC.  Blue and Red symbols are data of non-photonic electron v2 from PHENIX[i] and STAR[ii]. Only statistical errors are shown for both results.  The dashed-dotted-line represents the input D-meson v2 distributions, assuming the scaling of constituent quarks for meson v2. The corresponding decayed electron v2 are shown as the hatched band[iii]. The dashed-line represents the results from Greco[iv] et al.  In this coalescence calculation, similar v2 distributions for c- and u-quarks are assumed.  
Hence, thermalization of light quarks is likely to have been reached through partonic re-scattering. 
Figure 7 shows the first indication of charm particle elliptic flow at RHIC measured in the inclusive electron channel35,36.  [jt1]The predictions assume elliptic flow for the light quarks as determined by fits to experimental data.  Presently, the data support the idea that the heavy charm quarks flow.  As shown in the figure, the uncertainties are rather large especially at low transverse momentum where hydrodynamic behavior should occur. A precise measurement of directly reconstructed open charm hadrons to low momentum is essential to confirm and further quantify elliptic flow of the charm quarks.  
 [jt1]These are cross references and really should be the primary references, not cross.  Put the cross refs in the figure captions.

## Single Electron Spectra ... are not sufficient

**Hydro and Pythia are extreme models on opposite ends of the model spectrum **
**Charm in red, Beauty in Blue ... Hydro is the solid line, Pythia is dashed**
**Single electron spectra are not sufficient to distinguish hard and soft physics below 3 GeV**
**We will also see this in the R****AA**** measurements**
**The decayed spectra are shown in black and are nearly indistinguishable **
**We heard this message many times at QM05 and will hear it again at QM06**

- S. Batsouli et al., Phys. Lett. B 557 (2003) 26.

**We need direct topological identification of Charm**

**Notes:**
Figure 4: Solid- and dashed-curves represent the charm- (red) and beauty-hadron (blue) spectra from Blast-Wave and Pythia model calculations, respectively. The corresponding heavy flavor decayed electron spectra are shown as black curves.  The data are the measured single electron distributions measured in 10% central Au+Au collisions at 130 GeV by the PHENIX collaboration.  The figure is adapted from Ref. [20] 
When direct measurements of heavy flavor hadrons are not possible, non-photonic electrons from heavy flavor decays can be used to study charm production.  However,  there are serious limitations in such situations. As shown by Batsouli, Kelly, Gyulassy and Nagle in Ref. [[i]], the decayed electron distributions are insensitive to the intrinsic shape of the D-meson transverse momentum distribution. Due to the decay kinematics and the light mass of the electrons and positrons, the dynamical information in the primary spectrum is washed out.  This is shown in Figure 4.  There is a clear difference between the zero mean free path hydrodynamic flow prediction (solid) and the infinite mean free path pQCD Pythia calculations (dashed-line) for D-mesons; but the resulting electron spectra are nearly indistinguishable. In order to extract useful information about heavy flavor production in heavy ion collisions, we have to measure the charm and beauty-hadrons by direct topological reconstruction. Single electron spectra are not sufficient.  
[i] Batsouli et al., Phys. Lett. B557, 26 (2003).  nucl-th/0212068.

## Direct Topological Identification of Open Charm

- The STAR Inner Tracking Upgrades will identify the daughters in the decay and do a direct topological reconstruction of the open charm hadrons.
- No Mixed events, no random background subtraction.

- Goal: Put a high precision detector near the IP to extend the TPC tracks to small radius

## The Heavy Flavor Tracker

**A new detector**
**30 ********m silicon pixels**
**	****to yield 10 ********m space point resolution**
**Direct Topological reconstruction of Charm**
**Detect charm decays with small c********, including  D****0**** ******** K ******
**New physics**
**Charm collectivity     and flow to test thermalization at RHIC**
**Charm Energy Loss to test pQCD in a hot and dense medium at RHIC **
**R&D with HFT + SSD**
**A proposal has been submitted and a TDR     is in preparation**

**The Heavy Flavor Tracker**

## Inner & Forward Tracking Upgrades

**Inner & Forward Tracking Upgrades**

**The Inner Tracking Upgrade include**
**HPD  (1 layer)**
**IST  (2 layers)**
**The ITUp will add high quality space points to tracks in the TPC **
**Si at ******** = 0 **
**The FTUp will add high quality space points at forward ****η**
**1 < ****η**** < 2**
**High Rate tracking for heavy flavor physics and W production**

## Forward Tracking Upgrade

**e****+****/e****-**

**Forward Tracking Upgrade**

**Polarized pp program at √s = 500 GeV at RHIC at BNL: **
**Study the proton spin flavor structure of the proton spin**
**W detection via  W******** ******** e********   ****decay**
**identification of the e******** charge sign is critical**
**Employ triple-GEM detectors as part of STAR tracking upgrade **
**Low dead material, fast time response, precise hit determination, cost effective **
**Barrel or Disk configuration **
**With 4 conventional silicon disks in the forward direction**

## Surround the Vertex with Si

**Surround the Vertex with Si**

- The HFT is a thin detector using 50 m Si
- to finesse the limitations imposed by MCS

- Add the HPD, IST, and SSD to form the STAR Inner Tracking Upgrade ( ITUp )

## Goal: graded resolution from the outside – in 

**Goal: graded resolution from the outside – in **
**TPC – IST – HPD – HFT **
**TPC pointing resolution at the SSD is  ~ 1 mm**
**SSD pointing at the IST   is  ~ 300 ********m **
**IST pointing at the HPD  is  ~ 150 ********m **
**HPD pointing at the HFT  is  ~ 100 ********m**
**HFT pointing at the VTX   is  ~ 50 ********m**

## Double sided Si wafers 300 m thick with 95 m x 4.2 cm strips

Crossed at 35 mrad  –	effectively 30 m x 900 m

One layer at 23 cm radius

20 ladders, 67 cm long

air cooled

 < 1.2

1 % radiation length @  = 0

**Double sided Si wafers 300 ********m thick with 95 ********m x 4.2 cm strips**
**Crossed at 35 mrad  –****	****effectively 30 ********m x 900 ********m**
**One layer at 23 cm radius**
**20 ladders, 67 cm long**
**air cooled**
****** ****< 1.2**
**1 % radiation length @ ******** = 0**

## Singled sided Si wafers 300 m thick with 60 m x 4.0 cm strips

**Singled sided Si wafers 300 ********m thick with 60 ********m x 4.0 cm strips**
**Si pads  ~ 1 mm**2 on the other     side of each ladder**
**Two layers at 17 & 12 cm radius**
**27 ladders,  52 cm long**
**19 ladders,  40 cm long**
**air cooled**
****** ****< 1.2**
**1.5 %  per layer @ ******** = 0**

## ALICE Hybrid Pixels 350 m thick, with 250 m in the sensor and  150 m in the ASIC

**ALICE Hybrid Pixels 350 ********m thick, with 250 ********m in the sensor and  150 ********m in the ASIC**
**50 ********m x 425 ********m strips**
**One layer at 9.1 cm radius **
**48 ladders, 28 cm long**
**C****6****F****14**** Evaporative cooling**
****** ****< 1.2**
**1.1 % radiation length @ ******** = 0**

## Active Pixel Sensors, thinned to 50 m thickness

**Active Pixel Sensors, thinned to 50 ********m thickness**
**30 ********m x 30 ********m pixels**
**Two layers at 7 & 2.5 cm radius**
**24 ladders, 19.2 cm long**
**  ****9 ladders, 19.2 cm long**
**air cooled**
****** ****< 1.2**
**0.28 % radiation length @ ******** = 0**

## R&D in Run 7

**A Three Layer Telescope with MimoSTAR II Chips.**
**A full system test from pixel to DAQ using an extension of one TPC sector trigger line.**

## HFT R&D and Installation Timeline 

- Install MimoSTAR II
- Telescope

- X marks the installation dates.  Running comes *after*  installation.

- Proposed HFT Timeline – the HPD and IST come about 1 year later

## A Rich Physics Program	

**There is a rich physics program when all of the STAR physics detectors are working together**
**Flow in the Charm sector**
**dE/dx in the Charm sector**
**Recombination and R****AA**** in the Charm sector**
**Vector Mesons**
**Charm Angular Correlations**
**non-photonic electrons**
**...**

## Working with the rest of STAR   ...   (       )n

**	****Combining the power of the STAR TOF barrel to identify electrons with the ability of the TPC and Inner Tracking Upgrades to identify and eliminate conversion electrons means we can execute a vigorous single electron and di-electron program of measurements**

**Notes:**
Figure 12:  Left top: TPC dE/dx vs p in d+Au collisions.  Left bottom: TPC dE/dx vs p after TOFr PID selection of | 1- | < 0.03.   Clean electron identification is achieved.  Right: dE/dx from the TPC after TOFr PID selection for 1.0 < p < 1.5 GeV/c.[HM1]

At STAR, electron identification is made possible by a combination of two measurements: a measurement of the energy lost by charged particles due to ionization in the TPC gas (dE/dx), and a velocity measurement with the time-of-flight system.  The relativistic rise of the electron dE/dx separates the electron dE/dx from those of hadrons except at the crossovers with pions at a momentum of  ~ 0.2 GeV/c, kaons at ~ 0.6 GeV/c, protons at ~ 1.1 GeV/c and deuterons at  ~ 1.5 GeV/c.  A time-of-flight measurement, using a requirement that |1-| < 0.03, eliminates slow hadrons and cleans up the crossovers.  This results in clean electron identification, as shown in Figure 12. The top plot on the left shows the conventional dE/dx measurement in the TPC gas as a function of particle momentum. The bottom plot on the left shows the same dE/dx measurement but now requiring |1-| < 0.03 from the TOF detector.  The upper electron band is clearly separated from the lower pion band. Heavier particles (e.g. kaons and protons) are completely removed by the TOF requirement.  The right hand plot of Figure 12 shows a dE/dx projection in the transverse momentum range pT = 1.0-1.5 GeV/c.  Even at this rather large momentum, the distribution of electrons is clearly separated from the distribution of charged hadrons 

## Summary

**The STAR Inner Tracking Upgrade will explore the Charm sector**
**We will do direct-topological-reconstruction of open Charm**
**Our measurements will be unique at RHIC**
**The key measurements include**
**V****2**
**Energy Loss **
**Charm Spectra, R****AA  ****& R****cp**
**Vector mesons**
**Angular Correlations**
**The technology is available on an appropriate schedule**

**Supplementary slides**

## Si Pixel Developments in Strasbourg

**Mimosa – 1**
**4k array of 20 ********m pixels with thick epi layer**
**Mimosa – 4**
**Introduce Forward Biased Diode**
**Mimosa – 5  **
**1M array of pixels, 17 ********m pixels using AMS 0.6 process**
**4 msec readout scan rate**
**Mimosa – 8**
**Fast parallel column readout with internal data sparsification**
**200 ********sec readout scan rate**

**MimoSTAR – 1   128x128 pixels  using TSMC 0.25 **
**MimoSTAR – 2   128x128 pixels  using AMS 0.35**
**Duct tape these to the STAR Beam Pipe for 07 run **
**MimoSTAR – 3****	****320x640 pixels  using AMS 0.35**
**MimoSTAR – 4   640x640 pixels  production run**

**Ultra – 1**
**Ultra – 2**

## Addition Detail

## Copy the Alice HPD using only one layer

**Copy the Alice HPD using only one layer**

## HPD Ladders - Sector Layout

*Image: INFN Padova*

- HPD total ~ 1000 pixel chips, ≈ 107 pixels

- Kapton cables     MCM RDO section     active area

## HPD Ladder Cross-Section

- 7-layer
- Aluminum
- Kapton Flex
- 200 m
- 150 m

- M. Morel