? production in p p and Au Au collisions in STAR

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? production in pp and AuAu collisions in STAR

• Debasish Das
• UC Davis
• (For the STAR Collaboration)?

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Quarkonia and the concept of suppression
Charmonia J/?, ?, ?c Bottomonia ? (1S),
?(2S), ?(3S)?

• Heavy quarks carry the information of early stage
  of collisions
• Charm and bottom quarks are massive.
• Formation takes place early only in the
  collision.
• Proposed Signature QCD phase transition
• Color screening of static potential
  between heavy quarks
  J/??suppression Matsui and Satz, Phys.
  Lett. B 178 (1986) 416
• Suppression of states is determined by TC and
  their binding energy
• Lattice QCD Evaluation of spectral functions ?
  Tmelting
• Deconfinement ? Color screening ??heavy quarkonia
  states dissolved
• Tdiss(?) ? Tdiss(?c)lt Tdiss(?(3S)) lt Tdiss(J/?)
  ? Tdiss(?(2S)) lt Tdiss(?(1S))?
• Their suppression pattern is a thermometer of
  the QCD matter produced.

H. Satz, HP2006
2/17
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? States in RHIC

• ???????????S), ????S), ???S)?
• ?(1S) no melting at RHIC ? standard candle
  (reference)?
• ?(2S) likely to melt at RHIC (analogous to J/?)?
• ?(3S) melts at RHIC (analogous to ?)?

• Pros
• co-mover absorption is very small
• ( C.M.Ko PLB 503, 104)?
• recombination negligible at RHIC (?bb ltlt ?cc)?
• STAR has efficient ??trigger and large acceptance

• Cons
• extremely low rate 10-9/min. bias pp interaction
• need good resolution to separate three S-states

? measurements at RHIC ? challenge to understand
such rare probes
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STAR ? Mass Resolution

• STAR detector is able to resolve individual
  states of ????
• albeit Bremsstrahlung
• With current low statistics, yield is
  extracted from combined
• ?(1S2S3S) states
• FWHM 400 MeV/c2

With Inner Tracker small X/X06
W/o Inner Tracker Low X/X0
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STAR Detectors used for ? measurements
AuAu ? Event in STAR Trigger.

• EMC
• Acceptance ? lt 1 , 0 lt ? lt 2?
• High-energy tower trigger ? enhance high-pT
  sample
• Essential for quarkonia triggers

• ? trigger ? enhances electrons
• Use TPC for charged tracks selection
• Use EMC for hadron rejection
• Electrons identified by dE/dx ionization energy
  loss in TPC
• Select tracks with TPC, match to EMC towers above
  3 GeV

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STAR ? Trigger (pp 200 GeV in Run 6)?

• Sample ?-triggered Event
• ??ee-
• mee 9.5 GeV/c2
• cos? -0.67
• E1 5.6 GeV
• E2 3.4 GeV

charged tracks

• Full EMC acceptance ?lt1 in run 6
• Integrated luminosity 9 pb-1 in run 6

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STAR ? Trigger (AuAu 200 GeV in Run 7)?

• Sample ?-triggered Event
• ??ee-
• mee 9.5 GeV/c2 (offline mass)?
• cos? -0.77(offline opening angle)?
• E1 6.6 GeV (online cluster energy
• hardware trigger)?
• E2 3.2 GeV (online cluster energy
• software trigger)?

Electron Momentum gt 3 GeV/c
Challenging analysis!!!!!

• Full EMC acceptance ?lt1 in Run 7
• Integrated luminosity 300 µb-1 in Run 7

charged tracks
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QM 2006 ? in Run 6 pp at vs200 GeV Invariant
Mass

• Signal Background ? unlike-sign electron pairs
• Background ? like-sign electron pairs ?(1S2S3S)
  total yield integrated from 7 to 11 GeV from
  background-subtracted mee distribution
• Peak width consistent with expected mass
  resolution
• Significance of signal is 3s
• Note Contribution from Drell-Yan (9) ignored

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QM 2006 STAR ? vs. Theory and World Data
STAR 2006 vs200 GeV pp ??????ee- cross
section consistent with pQCD and world data
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? in AuAu at vs 200 GeV (Run 7)?
First Rough Look Using identical cuts
as in pp analysis. Pros
allows apples-to-apples comparison with pp
Cons not optimal for AuAu
larger
background, different trigger thresholds

• RAA Upper Limit ? RAAlt 1.3 at
  90 CL

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? in AuAu at vs 200 GeV (Run 7)?
Improved Analysis Pros improved
EMC-track-trigger handling ? strong signal and
enhanced S/B Cons trigger efficiency and
systematic checks not completed yet

• Strong 4? signal
• First measurement of ? in nucleus-nucleus
  collisions ever
• Too early for RAA but will provide good first
  measurement
• also need re-analysis of pp

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Summary and Outlook

• Full EMC trigger ? quarkonium program in STAR
• Run 6 first mid-rapidity measurement of
  ???S2S3S)?ee- cross section at RHIC in pp
  collisions at vs200 GeV
• Bee(ds/dy)y09128(stat.)22(syst.) pb
• STAR ? in pp measurement is consistent with pQCD
  and world data
• Run 7 We have the first ? measurement in heavy
  ion collisions
• for 200 GeV AuAu
• Strong signal
• Soon
• RAA of ?
• Run 8 measurement in dAu
• Absolute cross-section in pp, dAu, and AuAu
• RHIC II 20 nb-1 will allow separation of 1S,
  2S, 3S states

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Thanks!!!