The STAR Forward GEM Tracker Upgrade

1
The STAR Forward GEM Tracker Upgrade

• T. Hallman
• FGT Review
• Massachusetts Institute of Technology
• January 7- 8, 2008

2
The outline of this talk

• Scientific urgency of the FGT upgrade for
  STAR/RHIC
• General summary of project status
• Conclusions

3
The Science of STAR

• STARs primary science mission
• Discovery of a new state of matter (quark-gluon
  plasma) in central heavy ion collisions ( ?)
• Detailed unfolding of the spin structure of the
  nucleon (work in progress)
• Value added physics
• Low x structure of hadrons
• Fundamental tests of QCD
• Search for new exotics
• Forward inclusive spectra and correlations
• Tagged forward proton studies
• Ultra-peripheral collisions

4
What has been achieved in the ion program at RHIC
thus far

• RHIC has discovered the
• hottest (T200-400 MeV)
• densest (jet quenching ei30-60e0)
• matter (thermal yields)
• ever studied in the laboratory, which
• flows (large elliptic flow)
• as a (nearly) perfect liquid with systematic
  patterns consistent with
• quark degrees of freedom (valence quark
  scaling)
• and a viscosity to entropy-density ratio lower
  than any other known fluid, near
• a conjectured quantum bound (h/s 1-2 x 1/4p)

Next step quantitative
measurement of medium properties with
well-controlled systematic uncertainties
to determine e.g. shear viscosity, transport
coefficients, speed of sound, EOS, This also
requires timely completion of the RHIC II machine
and detector upgrades to allow access to rare
(hard) probes, and data sets with statistical
precision previously out of reach
5
What has been achieved in the spin program thus
far?

• ? toward understanding the proton spin.
• ALL for inclusive jets and di-jets at ?sNN 200
  GeV strongly disfavors large positive (negative)
  gluon polarization (suggests ?G may be small)
• Di-jet Sivers effect measurement (sensitive to
  orbital motion) shows observed asymmetries are an
  order of magnitude smaller than seen in SIDIS at
  HERA (cancellation of initial vs final state and
  u vs d quark contributions?)
• ? toward measuring transverse spin preferences
• Unexpected increase of AN with pT (very
  surprising given expectations from pQCD)

Every measurement brings fundamentally (often
unexpected) new insights deepening the quest to
understand the inner workings of the proton
We are further than ever before ? but still very
much in need of additional pieces to the puzzle
including the flavor dependence of the polarized
(anti) quark sea (and hence its origin)
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Why is that important and what will this upgrade
provide uniquely ??deeper insight into
contribution from the quark sector

• DIS has shown combined quark and anti-quark spins
  contribute only 20 of the nucleon spin
  (keyword combined)
• In the quark sector, SIDIS is one approach to
  learn more, but subject to (unknown) details of
  the fragmentation process.
• Presently the combined sum of the quark
  anti-quark polarization, e.g., x(?u ?u ), is
  well known but individually the anti-quark
  distributions ?u, ?d are unconstrained. Some
  progress expected at JLAB (E04-113) where ?uv,
  ?dv, and the difference ?u - ?d will be
  measured in a complementary range of x (0.12
  0.41) and Q2 (1.21 3.14 GeV2)
• The proposed FGT upgrade will allow a major
  advance direct sensitivity to the ?u, ?u, ?d,
  ?d distributions separately using single
  longitudinal asymmetry of W decays.
• This essential capability is unique at RHIC and
  complementary between PHENIX and STAR
• The FGT will also afford capability needed to
  constrain unpolarized quark distribution
  functions at large x, allowing RHIC to determine
  the size of the polarized flavor asymmetry (?u -
  ?d) relative to the flavor asymmetry for the
  unpolarized distributions
• ( d(x) / u(x) gt 1.6)

Caveat We detect/track leptonsnot Ws. To work
this measurement has to be made at forward
(backward) pseudo-rapidity where the lepton
asymmetry in ? and pT is strongly correlated with
the parent W. Because of limitations of
existing tracking detectors that means these
measurements can not be made in STAR without the
FGT.
These measurements will bring fundamentally new
insights into the nature and origin of the
polarized sea in the proton
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Wider significance for Nuclear Physics? Galveston
Long Range Plan Meeting fundamental
science at RHIC (heavy ion and spin) in the next
decade?
H1. Quantitative determination of viscosity
(h/s). Thus, clearly answering the
question is QCD matter the most perfect fluid?
H2. Quantitative determination of color field
strength via qhat. H3. Heavy quarkonia and
light vector meson probes to determine
color interactions in medium. Direct connection
with lattice QCD. H4. Experimental verification
or null result on critical point. H5.
Detailed measurements of collective excitations
of the fluid and extraction of medium
properties (e.g. speed of sound). H6.
Quantitative understanding of gluon saturation Qs
in Au S1. Mapping out of gluon contributions
Dg(x) as a function of x. S2. Determination of
DG with comparable errors to DS. S3.
Measurement of sea quark polarization via W
bosons. S4. Detailed study of transverse spin
physics (including information on orbital
angular motion).
This is a DOE milestone for 2013 for which STAR
must have the capability provided by the FGT
to be successful C-AD has already
demonstrated proof of principle accelerated,
stored beam with substantial polarization at
?s 410 GeV
8

• The near-term big picture physics goals of
  the STAR program are
• Run 8 Saturation scale for the
  gluon distribution in relativistic heavy nuclei
  (FMS)
• Transverse
  spin/motion preferences of quarks/gluon in the
  proton (FMS)
• Run 9 Comprehensive study of
  resonances and their hadronic and leptonic decays
• (TOF DAQ1000)
• Correlations of
  hadrons non-photonic electrons from D, B
  semi-leptonic decays
• (TOF DAQ1000)
• x dependence of ?G(x)
  at ?s 200 GeV (benefits greatly from DAQ1000)
• Run 10 Definitive search for the
  existence and location of the QCD Critical Point
  (TOF)

STAR is counting on having this capability for
the first significant ?sNN 500 GeV data
taking timely beginning of construction of FGT
is urgent
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The Upgraded STAR Detector


GEM
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Short Synopsis of STAR Upgrade Plans

• Forward Meson Spectrometer ? Just Completed
• Gluon density distributions, saturation effects,
  and transverse spin
• DAQ Upgrade
• order of magnitude increase in rate ? rare probes
  studies with no dead time
• extra bandwidth opens the door to value added
  physics
• Full Barrel MRPC TOF
• extended particle identification at intermediate
  pT
• Forward GEM Tracker
• end cap tracker for W sign determination
• Heavy Flavor Tracker
• high precision Heavy Flavor Tracker near the
  vertex
• opens the door to direct, event-by-event
  topological ID of Charm Beauty
• Muon Telescope
• Forward Reaction Plane Detector
• A Crystal Calorimeter for low E photons
• ?-? HBT

Well Underway
Proposal /Final Design
Concept Dev.
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Physics Driven Requirements

• Requirements on FGT
• Fit into envelope vacated by West FTPC
• Support structure must be compatible with SSD and
  new IST
• Dead material for ? gt 1 less than 1 X0
• High efficiency for charge separation out to ?
  2 for the full vertex distribution ( z lt 30
  cm) for particles having pT up to 40 GeV/c
• Capable of operation and of handling pile-up at
  RHIC II luminosity
• (4 ? 1032 cm-2s-1 for ?s 500 GeV pp )
• Readout compatible with DAQ1000 upgrade
  (dead-timeless operation at 1000 Hz)
• Additional requirements including other STAR
  systems
• Effective e/h separation
• Efficient triggering on high pT e from W decays

The proposed system meets these requirements
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In this game, Kinematics Physics, and..

• Partonic kinematics related to W rapidity
• Lepton rapidity related to W rapidity
• lepton rapidity determined from pt

• you have to measure the lepton at forward
  rapidity,
• you dont know anything unless you get the sign
  of the lepton right
• cross sections are small every W counts

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Why is the Forward GEM Tracker Crucial?
Probability to get the correct charge sign
Probability to get the correct charge sign
Reach of EEMC Acceptance
?
?
TPC Tracking Only, pT 30 GeV/c
TPC FGT Tracking, pT 30 GeV/c
Conclusion for 6 triple-GEM disks, assumed
spatial resolution 60 µm in x and y charge
sign reconstruction probability above 80 for 30
GeV pT over the full acceptance of the EEMC for
the full vertex spread ( gt 90 out to ? 1.8)

• Conclusion
• Charge sign reconstruction impossible
• beyond ? 1.3

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Simulation of System Performance
Track Reconstruction Efficiency
Charge Reconstruction Efficiency
Efficiency
Efficiency
Generated ?
Generated ?
TPC EEMC SMD Vertex
constraint Measurement not feasible for large
of EEMC Acceptance!
TPC EEMC SMD Vertex constraint FGT
TPC EEMC SMD Vertex FGT SSD IST
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Schematic layout of the STAR FGT

• 6 triple GEM disks, 40 cm radius
• each disk consists of 4 detectors

1.6M lt Range of project cost lt 1.8M Leveraged
by significant contributed resources Foil
technology in development through SBIR
collaboration

• 3 GEM foils per disk to reach high gain with high
  stability
• 2D readout board each detector layer provides a
  space point

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FGT Technically Driven Schedule
The reason this aggressive schedule is
feasible is that the RD and conceptual design
are far along
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Basic Detector Performance Proven
Overall Resolution 72 ?m Resolution of 72 ?m
on position of peak
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STAR FGT Cost Estimate (FY08 k)
(Contingency and overhead included ? MIT overhead
assumed for materials)
Materials Labor

• DAQ 92 182
• Front-End Electronics 95 267
• Triple-GEM Detector 415 239
• Integration 240 258
• Infrastructure 28 89
• Installation 274
• Total
  870 1050

Total Project Cost including all DOE investment
1,920k
Offsetting non-DOE contribution from Univ. of
Kentucky for materials 100k
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STAR Perspective on FGT Upgrade

• Importance of the FGT upgrade for STAR/RHIC ?

• Its crucial, STAR is anxiously waiting for this
  new capability to
• Make measurements with direct sensitivity to
  the ?u, ?u, ?d, ?d distributions
• separately to further understand
  contributions to the proton spin in the quark
  sector
• Constrain unpolarized quark distribution
  functions at large x, allowing RHIC to
• determine the size of the polarized flavor
  asymmetry (?u - ?d) relative to the flavor
• asymmetry for the unpolarized distributions
  ( d(x) / u(x) gt 1.6)
• Afford isolation cuts for direct photons and
  improve reconstruction of particles in jets to
• enhance ? jet determination of ?G(x) in
  crucial forward region of STAR acceptance
• Reduce non-vertex beam background and improve
  z vertex resolution in pp interactions

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Conclusions

• Scientific mission is clear scientific merit
  very high in international
• perspective need is urgent
• Basic detector performance and foil production
  feasibility demonstrated
• through completed RD
• General project status optimized concept
  exists which meets physics
• driven requirements
• Simulations on performance / final tuning of
  design in progress
• Basic feasibility of design proven
• Preparation for construction project ongoing
• Strong committed team in place, working hard

STAR is anxious to get at the science this
upgrade will make possible
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Backup Slides
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Run 5 results and projected Run 6 sensitivity on
inclusive jet production in pp collisions at ?s
200GeV
These results will place a world-class constraint
on gluon polarization in the proton, ?G
23
STAR Run 6 di-jet Sivers effect
measurementarXiv0705.4629, Submitted to PRL May
27
Fundamental question Is there a correlation
between proton transverse spin and parton
transverse momentum (Sivers effect)?



Blue beam asymmetry
Yellow beam asymmetry
Asymmetry (for proton spin and momentum shown)
(No. of di-jets folded to the left) ( No.
folded to the right) (No. of di-jets
folded to the left) ( No. folded to the
right)

• From Run 6 data thus far
• Observed asymmetries are an order of magnitude
  smaller than seen in semi-inclusive
  deep-inelastic scattering by HERMES
• Possible explanation cancellations of initial
  vs. final state and u vs. d quark contributions,
  ? and gluon effects are small