# 6. ENDCAP Extension

## Introduction {#introduction .unnumbered}

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 40x 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/image1.jpeg){width="4.331944444444445in" height="2.26875in"}

Figure 1. Cross-section view of the proposed vertex detector.

![](media/image2.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.

## 6.1 Goals of the Endcap Upgrade {#goals-of-the-endcap-upgrade .unnumbered}

### 6.1.1 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/image3.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.

.

### 6.1.2 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/image4.png){width="4.034722222222222in"
height="3.3833333333333333in"}

### 6.1.3 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
:

####  {#section-1 .unnumbered}

#### 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. 

####  {#section-2 .unnumbered}

![](media/image5.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.

## 6.2 Simulations and Required Performance for the Si Endcap Upgrade {#simulations-and-required-performance-for-the-si-endcap-upgrade .unnumbered}

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.

    -   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.

    -   Good resolution in both r and z are required.

    -   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 ministrips vary in size from 50m by 2000m to 50m by 9000m as
the radius increases. This keeps the occupancy at or below 1.5%.

### 6.2.1 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/image6.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/image7.jpeg){width="3.682638888888889in"
height="3.682638888888889in"}

To calculate the yield of charm, we assume a 350 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.

### 6.2.2 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[^1]. 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/image8.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.

### 6.2.3 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.

###  6.2.4 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
  ------------------------------------------------------------- -----------------------------------

### 6.2.5 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.

### 6.2.6 Integration with PHENIX

The proposed Endcap vertex detector matches and extends the capability
of the existing muon spectrometer arms. In addition a joint HBD/TPC is
being proposed to sit outside the vertex detector. The Detector Advisory
Committee recommended studies exploring the impact of the VTX on the
HBD/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.

## 6.3 Technical Aspects of the Proposed Endcap Vertex Detector {#technical-aspects-of-the-proposed-endcap-vertex-detector .unnumbered}

### 6.3.1 Silicon Readout Chip --PHX

Ray Yarema's group at Fermilab 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 um by 400 um 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 ministrips. 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 um 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.

### 6.3.2 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 ministrips
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 ministrips. The smaller sensors contain 2560
and 1536 strips.

![](media/image9.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/image10.jpeg){width="1.3493055555555555in"
height="3.435416666666667in"}![](media/image11.jpeg){width="1.8847222222222222in"
height="3.6840277777777777in"}![](media/image12.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/image13.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/image16.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/image17.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.

### 6.3.3 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.

### 6.3.4 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.

### 6.3.5 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/image18.jpeg){width="2.8055555555555554in"
height="2.502083333333333in"}
![](media/image19.jpeg){width="2.2118055555555554in"
height="2.7527777777777778in"}

##   {#section-3 .unnumbered}

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/image20.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.

[6.3.6 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/image21.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.

## 6.4 R+D Schedule, Responsibilities and Budget {#rd-schedule-responsibilities-and-budget .unnumbered}

### 6.4.1 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/image22.wmf)

### 

### 6.4.2 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 a collaboration with Ecole Poly-Technique and
Saclay, who will contribute to both the hardware and software efforts.

[^1]: E789 Phys. Rev. Lett. 74, 3118 (1995).