Heavy Flavor from STAR

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Heavy Flavor from STAR

• Saskia Mioduszewski
• for the STAR Collaboration
• Texas AM University
• 30 May, 2009

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Heavy-Ion Collisions

• Collide heavy ions to create new form of matter
  in which quarks and gluons are deconfined
• Characterize matter by temperature, density,
  degree of thermalization, signatures of
  deconfinement
• Heavy Flavor represents an important such probe
  of the medium

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Why Heavy Flavor?

• Large-mass quarks provide particularly good probe
  of medium produced
• mc 1.3 GeV, mb 4.8 GeV gtgt Tc, LQCD ?
  maintains identity in medium
• Created in the initial collisions
• Provides direct connection to transport
  properties of medium
• What Questions Can be Addressed via Heavy Flavor?
• Open Charm/Beauty energy loss mechanism, degree
  of thermalization
• Quarkonium deconfinement (dissociation in QGP),
  degree of thermalization

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The STAR Detector
Large acceptance 2? coverage at mid-rapidity
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, TOFr PMD Year 2001
Upgrades Time of Flight, DAQ1000, Heavy Flavor
Tracker, Muon Telescope Detector
QM09 Knoxville TN
12/16/2009
4/23
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High pT Suppression at RHIC
PLB 655(2007)104
Gluon bremsstrahlung should be reduced for
heavier particles (i.e. heavy quarks) propagating
through medium
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One of the most surprising results from RHIC
Heavy Flavor measured via non-photonic electrons
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One of the most surprising results from RHIC
CuCu data consistent with Npart dependence of
suppression
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Do we understand energy loss mechanism?

• Suppression of heavy-flavor decay electrons as
  large as for light mesons
• Not expected by predictions for radiative energy
  loss ? led to inclusion of collisional energy
  loss in theoretical calculations
• Where is Beauty contribution?

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Electron-tagged correlations to obtain beauty
contribution

• Experimental approach
• - non-photonic electrons from semi-leptonic charm
  decays are used to trigger on c-c, b-b pairs
• back-2-back D0 mesons are reconstructed via
  their hadronic decay channel (probe)?
• Underlying production mechanism can be
  identified using second charm particle

heavy quark production
???0
????
flavor creation gluon splitting/fragmentation
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Heavy quark production in pp collisions
e-h results agree with e-D0 correlation

• - the B contribution to non-photonic
  electrons is 50 at pT5 GeV/c, based on e-h and
  e-D correlations

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Conclusions for Open Heavy Flavor

• Data cannot be described by calculations of
  radiative energy loss (gluon bremsstrahlung)
  alone
• Stronger constraint taking into account
  significant contribution of beauty
• Elastic energy loss component must be included

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Heavy Quarkonium

• Production Mechanism of J/Y state not understood
• Several models exist (COM vs. CSM)
• RHIC provides new data at vs 200 GeV

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Heavy Quarkonium Production
arXiv0904.0439
J/Y Production in pp collisions
vs Dependence
STAR strength measurement at high pT
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J/Y Suppression
We expect a suppression of bound states due to
color screening in the Quark Gluon Plasma.
(Matsui Satz, 1986)
Data from SPS, showing J/Y suppression

• Charm cross-section larger at RHIC than SPS
  20 cc pairs produced per collision
• We have evidence that charm may be partially
  thermalized at RHIC ? recombination of cc pairs
  to regenerate J/Y ?
• Or sequential melting of charmonium (Karsch,
  Kharzeev, Satz)

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Heavy Quarkonium Production (and Survival)

• Data consistent with no suppression at high pT
• Indicates RAA increase from low pT to high pT
  
• AdS/CFT H. Liu, K. Rajagopal and U.A.
  Wiedemann, PRL 98, 182301(2007) and
  hep-ph/0607062
• Two Component Approach X. Zhao and R. Rapp,
  hep-ph/07122407

arXiv0904.0439
Only hadron observed at RHIC with no suppression
at high pT
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J/? Hadron Correlations
arXiv0904.0439

• Limits on feed-down from B
• 13 5 (if production in PYTHIA is correct)

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Upsilon Measurements
Run-8 dAu collisions

• Upsilon
• can serve as thermometer of medium (want to
  resolve different states)
• can help understand J/y suppression vs.
  regeneration
• ? Need high luminosity

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Future Measurements

• Direct Topological Reconstruction of Open Charm
  Hadrons - to help understand energy loss and
  thus medium properties

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Conclusions

• Surprise at RHIC heavy-quark energy loss does
  not follow expectation Do we really understand
  energy loss mechanism?
• Beauty contribution to heavy flavor decay
  electrons is 50 at pT5 GeV/c, indicating that
  bottom may be suppressed as well
• Need direct measure of open charm hadrons up to
  high pT will be possible with planned upgrades
• J/Y not suppressed at high pT, contrary to all
  other hadrons measured at RHIC
• Upsilon measurements will help to understand J/Y
  data at low pT (suppression vs. recombination)