STAR: update on Strangeness and Heavy Flavor

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STAR update on Strangeness and Heavy Flavor

• Olga Barannikova
• for the STAR Collaboration

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Outline

• Selected recent STAR results on strangeness and
  heavy flavor production
• Medium properties
• Thermalization
• Particle production and Parton propagation
• Energy density Energy loss
• Summary

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But first Hypernuclei at RHIC
Hypernucleus - Nucleus which contains at least
one hyperon in addition to nucleons.
Hypernucleus of lowest A - Hypertriton
Saito, HYP06
First discovery Danysz and Pniewski in 1952
Hypernucleus experiments SPHERE at
JINR Jlab HypHI at GSI/FAIR J-PARC
(2009) PANDA at FAIR (2012) .
No one has ever observed any antihypernucleus
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observation
3LH mesonic decay, mass2.991 GeV, BR 0.25 200
GeV AuAu data

• Hypernucleus Discovery in HI at RHIC 6s
  combined signal
• First ever observation of an anti-hypernucleus
  4s signal
• The hypertriton and anti-hypertriton lifetime

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Strangeness studies Motivation

• Why bother?
• Produced in the collision
• Small rescattering cross-sections

• Phase-boundary/hadronization probes
• Equilibration?
• Enhancement of strangeness one of the earliest
  QGP predictions
• Flavor dependence of energy loss

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Strangeness production at RHIC

• Detailed systematic studies with multiple systems
• Evidence of s-quark equilibration in central
  AuAu collisions
• Enhancement of strangeness production in AuAu,
  CuCu, dAu

STAR, PLB616 (2006) 637
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Thermalization studies strange particles V2

• Mass ordering in the low pT is well established
  with common hadrons

• Multi-strange hadron v2 ?
• Partonic collectivity
• Hadronization via coalescence

Run 7
Open symbols PHENIX, PRL 98 (2007) 162301
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High pT strangeness

• Kaon production (wrt. pions) is enhanced up to
  highest pT
• Suggestive of jet-chemistry modifications

W. Liu and R. Fries, PRC 77, 054902 (2008)

• Partons conversions may be significant due to
  interactions with the medium
• Abundant QGP s-quarks result in boost of Kaon
  production factor 2

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Jet flavor conversion
STAR Preliminary
W. Liu and R. Fries, PRC 77, 054902 (2008)

• Expectation from color charge dependence of
  energy loss RAA(p) lt RAA(?)
• Observation from central AuAu collisions
  RAA(?) ltRAA(K) ltRAA(p)
• Hierarchy consistent with jet flavor conversion
  
• parton ?medium interactions

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Yichun Xu, 5A Anthony Timmins, 6C
Jörn Putschke for the STAR Collaboration, QM09,
Knoxville
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Heavy Flavor studies Motivation

• Why Heavy Flavor?
• Produced in the early stages
• Heavy quarks calculable (?) probes for medium
  properties
• Discriminating power for energy loss scenarios

• Open Heavy Flavor pQCD tests of thermalization
  and energy loss mechanisms
• Quarkonia production mechanisms
• deconfinement and thermalization
  tests

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High pT suppression for HF

• Light flavor energy loss
• Strong suppression at high pT in RAA
• Jet studies via correlations softened spectra,
  broadening
• Radiative vs. collisional energy loss

• Open heavy flavor
• Smaller gluon bremsstrahlung for heavy quarks
  ?
• Smaller suppression at high pT

RAA for non-photonic electrons (from heavy flavor
decays)
No decrease in suppression for non-photonic e
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Energy loss for beauty

• Heavy Flavor results from non-photonic
  electrons
• Strong suppression of heavy-flavor at high pT
  in RAA light mesons
• Inconsistent with radiative energy loss
  prediction ? needs collisional too
• What about beauty?

e D0 correlation using like-sign e-K pairs

• Significant contribution from b-decays
• 50 at pT5 GeV/c

mostly B
25B,75C
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Charm and Beauty in pp
e-hadron correlations

• Agreement on b- and c- fractions from e-h and
  e-D0 correlation results
• b-decays contribution to non-photonic electrons
  50 at pT5 GeV/c
• ? strong suppression in AA for both charm and
  beauty!

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Quarkonia as temperature probes

• Systematic studies of multiple states (J/?, ?,
  ?C,?) could serve as a thermometer for QCD
  matter
• TD (?) 4Tc
• TD (?) TD (J/?) ?
• ?/ ?, J/? /? vs. pT very sensitive to system
  temperature size

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J/? measurements at high pT
STAR Preliminary
CS Color Singlet CO Color Octet
STAR Preliminary
First high pT J/? measurements Constrains on
production mechanisms Direct QCD CSCO in
agreement with data, little room for
feed-down NNLO CS predicts steeper pT spectra
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J/? production mechanisms and RAA
pp collisions
CuCu collisions
J/?-h correlation
STAR Preliminary

• Small background at high-pT in pp? J/?- hadron
  correlations
• Use the correlation function to measure the B?J/?
  fraction 13 5
• Contrast to AdS/CFT Hydro prediction (99 C.L.)
• RAA(pTgt5GeV/c) gt 0.6 (97 C.L.), indicating RAA
  increases with pT

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J/? at forward rapidity
Invariant mass of ee- pairs (J/?) with a photon
requirement
Invariant mass of all cluster pairs
counts
?C ? J/? ? ? e e- ? Significance2.9s
J/? ? e e- Significance 4.5s
First observation of high-xF(0.4) J/? beyond ISR
energies
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Upsilon production in dAu

• Run8 dAu 200 GeV
• High luminosity 32nb-1
• Low material in front of TPC
• L0L2 Upsilon trigger

Recall Run 6 pp 200 GeV Signal significance 3s
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Nuclear modification factor
pp
dAu
RdAu 0.98 0.32 (stat.) 0.28 (sys.)

• Consistent with Nbin scaling
• Consistent with anti-shadowing calculations

First ? signal in AuAu
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Summary

• STAR Systematic studies of the partonic
  medium
• First observation of anti-hypernucleus
• Systematic studies of strangeness at RHIC
• - Precision PID v2, NCQ test
• - Strangeness enhancement in different systems
• - Color-charge effects / jet flavor conversion
• Ongoing heavy flavor program
• High pT suppression both Charm and Beauty?
• J/psi RCuCu consistent with unity at high pT
• Upsilon Nbin scaling in dAu
• - Prospective RAA for Upsilon to understand J/psi
  (suppression vs. recombination)

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Back-Up
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signal from the data

• Signal observed from the data (bin-by-bin
  counting) 15730
• Mass 2.9890.0010.002 GeV Width (fixed)
  0.0025 GeV.
• Projection on anti-hypertriton yield
  1572168/5810 5911

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signal from the data

• Signal observed from the data (bin-by-bin
  counting) 7017
• Mass 2.9910.0010.002 GeV Width (fixed)
  0.0025 GeV.

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Heavy Flavor measurements
non-photonic electrons
D0 reconstruction
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J/Y Suppression at SPS