STAR%20Heavy%20Flavor%20Capabilities%20in%20the%20RHIC%20II%20Era

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STAR Heavy Flavor Capabilities in the RHIC II Era

• James C. Dunlop
• Brookhaven National Laboratory

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Kinetic Thermalization Open Charm Flow
F. Laue et al, nucl-ex/0411007
Test mechanism for thermalization charm heavy,
so needs many collisions to reach kinetic
equilibrium. Current measurements indirect from
electrons, and so suffer from large statistical
and systematic errors Need direct open charm
reconstruction (at low pT)!
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Chemical Equilibration Open Charm Yields

• No thermal creation of c or b quarks m(c)
  1.1GeV gtgt T
• c and b quarks interact with lighter quarks ?
  thermal recombination ?
• Ds/D0 very sensitive
• J/y suppression vs recombination ?
• Precision necessary for J/y, dilepton baseline

Pythia p-p 200 GeV Au-Au Thermal
D/D0 0.33 0.455
Ds/D0 0.20 0.393
Lc/D0 0.14 0.173
J/y/D0 0.0003 0.0004 No suppression
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Heavy Quark Energy Loss
Flavor dependence of coupling Less radiation,
and so less suppression, for massive objects

• vacuum radiation suppressed
• in the dead-cone q lt m/E

Dokshitzer, Kharzeev, PLB 519 (2001) 199

• medium-induced radiation
• fills the dead-cone

Armesto, Salgado, Wiedemann, PRD69 (2004) 114003
massive
dI/dk2
massless
dead cone
k2
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Temperature and density Onium
Yields and Spectra of the onium states (J/?,
Upsilon, and excited states) to measure the
thermodynamics of deconfinement through varying
dissociation temperatures
To deeply probe the plasma through studies of
(Debye) screening length l 1 /gT and map
in-medium QCD potential Study vs.
Pt Study vs. centrality Study in
lighter systems Study vs. a control ( the
Upsilon)

• Upsilon rate 10-3 ? J/Y
• Yield in 10 weeks of AuAu
• running at design luminosity

This physics requires luminosity upgrade
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The STAR Detector
Magnet Coils Central Trigger Barrel
(CTB) ZCal Time Projection
Chamber (TPC) Year 2000
Barrel EM Cal (BEMC) Silicon Vertex Tracker
(SVT)Silicon Strip Detector (SSD) FTPCEndcap
EM CalFPD TOFp, TOFrYear 2001
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STAR (Central) Coverage
p
Endcap EMC
Barrel EMC
Tracking (TPC,SVT,SSD)
Tracking (TPC,SVT,SSD,HFT)
Tracking (degraded)
f
TOF
-p
-1
1
2
0
h
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Upgrades relevant to heavy flavor

• Barrel Electromagnetic Calorimeter (EMC)
• Current ¾ barrel will be instrumented to full
  azimuthal coverage, -1 lt h lt 1, for next RHIC run
• Barrel Time of Flight (TOF)
• Current prototype patches to be upgraded to full
  azimuth, -1 lt h lt 1.
• Project is in Presidents budget.
• Forward Meson Spectrometer (FMS)
• Full azimuthal EM Calorimetry 2.5 lt h lt 4.0
• Possibility of charm measurements in this region
• Proposal submitted to NSF
• Data acquisition upgrade (DAQ1000)
• Upgrade TPC readout an order of magnitude,
  double effective Luminosity
• Heavy Flavor Tracker (HFT)
• High precision (lt10 um) measurements for
  displaced vertices

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PID Capabilities I TOF and TPC
PRL 94 (2005) 062301
Electron identification TOFr 1/ß-1 lt 0.03
TPC dE/dx electrons!!!
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PID Capabilities II EMC

• TPC as a candidate selector
• dE/dX for p gt 1.5 GeV/c
• Electrons can be discriminated from hadrons up to
  gt8 GeV/c

• EMC
• Towers
• p/E for electron and hadron candidates
• p is the track momentum
• E is the tower energy
• Peak position depends on the distance to the
  center of the tower

• SMD (Shower Max Detector)
• Shower cluster type
• Type 3 both SMD planes
• Track-SMD cluster distance
• Hadrons have a wider distribution

• e/h discrimination power 105
• TPC 500
• EMC 250

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PID Capabilities III Direct Reconstruction
PRL 94 (2005) 062301

• Direct reconstruction using Minv
• Uncertainty limitation is combinatoric background
• TOF cleanly identify daughters
• HFT identify displaced vertices

NEvents for 3s D0?Kp Signal
pT range TPC PID TPC TOF FOM
All 12M 2.6M 4.6
2-4 GeV/c 59M 23M 2.6
4-6 GeV/c 85M 42M 2.0
gt6 GeV/c 115M 115M 1.0
Number of AuAu events required for 3s signal.
FOMreduction in Nevents from TOF
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More demanding reconstruction
D0 ? K p using HFT, 50M events

• From only 50M events, additional rejection power
  of HFT leads to extremely small uncertainties in
  both spectra and v2
• Charm quark flow can be fully addressed with
  this upgrade
• Also Measure Ds ? f p

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Triggering Capabilities from the EMC

• EMC provides a Level 0 high-pT electron trigger
• Runs for every RHIC crossing (10 MHz)
• Multiple ET thresholds in prescale ladder
• For this plot, 2.5 and 5 GeV
• Enhancement proven to be gt1000 for pT gt 5 GeV/c

• More sophisticated triggers
• Upsilon
• Limited only by luminosity
• 15K Upsilon in 30 nb-1
• J/Psi
• Needs TOF for discrimination in AuAu

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DAQ Limitations (and their removal)

• Current limit from TPC front-end electronics is
  100 Hz
• Limits size of datasets
• 100M events/nominal RHIC run
• Affects available luminosity
• Deadtime scales linearly with rate
• 50 Hz 50 dead, i.e. 50 drop in luminosity
  available to rare triggers usual compromise
• Proposal to replace TPC electronics with ALICE
  chips to increase maximum rate by order of
  magnitude
• Rate of events to disk increased (though timely
  processing of events on disk is an issue)
• Removes deadtime effective doubling of RHIC
  luminosity

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Photonic Background
PRC 70 (2004) 044902

• STAR reconstructs p0, g from conversions in
  material inside the TPC
• Crucial cross-check of material budget
• Sweet spot 6 radiation length from vertex to
  TPC
• Removal efficiency from low Minv cut 60

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Photonic Background II

• Current methods
• Photonic electrons dominate below 1 GeV/c
• Clear nonphotonic signals above

g ? ee-
Future capabilities Large suppression by
HFT Enabling technology for low-mass dilepton
measurements
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b quark measurements

• B mesons accessible using semileptonic decay
  electrons
• Issue nonphotonic electrons will be measured,
  but what is the real fraction of these from B?
  Highly model dependent
• Using displaced vertex tag may be the ONLY
  reliable method

pT 15 GeV/c s (AuAu) 20mb/Gev ?30
nb-1 yields 600K b-bar pairs
Non-photonic electrons in dAu
Tagging in AuAu (w/ HFT)
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Summary

• STAR has proven capabilities for heavy flavor
  measurements at RHIC
• Electron identification using three detector
  systems (TPC, TOF, EMC) from 1 to gt10 GeV/c
• Photonic background rejection using topological
  methods
• Triggering capabilities to utilize full
  luminosity for rare probes
• Direct reconstruction of charmed mesons
• STAR has a clear path for improving its
  capabilities
• Completion and extension of calorimetric coverage
• Extension of TOF coverage to full azimuth for
  electrons and combinatoric background rejection
  in direct reconstruction
• Upgrade of Data Acquisition to increase effective
  luminosity and untriggered data samples
• Installation of the heavy flavor tracker for
  displaced vertices