Latest Results on Jet Quenching from STAR

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Latest Results on Jet Quenching from STAR
Lijuan Ruan (for the STAR Collaboration) (Brookha
ven National Laboratory)

• Outline
• Motivation and introduction
• Hard probes
• Identified particle at high pT
• High pT kaon production in pp and
  AA
• Quarkonia high pT J/?
• Hadron-hadron correlations in pp and AA
• ?-h correlation
• Full jet reconstruction
• New ridge results
  
• Summary and outlook

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To further understand energy loss mechanisms and
medium properties

• Color charge dependence g q (CA/CF9/4) protons
  versus pions
• g q jet conversion in the medium protons versus
  pions, kaons versus pions
• Flavor dependence light q versus heavy Q
  enon-photonic versus light hadrons
• Understand particle production mechanisms in pp
  reference
• STAR, PLB 637 (2006) 161, PLB 616 (2005) 8

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Kaon in 200 GeV pp at high pT
Spectra in pp collisions at pTgt2 GeV/c
convolution of PDF?pQCD?FF Charged and neutral
kaons are extended up to 15 GeV/c in pp
collisions. Charged and neutral kaons are
consistent provide constraints on FFs.
Low pT KS STAR Phys. Rev. C 75 (2007) 64901
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Measure fragmentation functions in pp
Jet algorithms SIS, kt, anti-kt Jet
Cuts Recoil WRT trigger Resolution parameter
(radius) lt 0.4 ? lt 0.6 Charged track, Tower
Energy pT gt 200 MeV/c V0 pTgt1 GeV/c Correction
applied double counting Missing energy and
energy resolution, tracking efficiency not
corrected for

• Pythia reproduces K0S fragmentation functions OK,
  deviations observed for strange baryons

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Jet hadro-chemistry in AuAu and pp
STAR Preliminary
STAR Preliminary

• The final jet hadro-chemistry change was
  observed
• K/? (AuAu) gt K/? (pp) RAA(ppbar) ? RAA(K) gt
  RAA (?) RAA(?)
• Consistent with jet conversion mechanisms and/or
  modified enhanced parton splitting in the hot,
  dense medium S. Sapeta and U.A. Wiedemann,
  arXiv0707.3494

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Jet hadro-chemistry in AuAu and pp

• Model comparisons
• Need detailed modeling of enhanced parton
  splitting and jet conversion
• Expanding medium
• Improved fragmentation function, which our data
  will provide better constraints on.
• High pT K measurements in dAu,
• centrality dependence in AuAu and v2

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High pT J/? RAA

• Consistent with no suppression at high pT
  RAA(pTgt5 GeV/c)
• 1.4 0.40.2
• RAA(pTgt5GeV/c) gt 0.6
• (97 C.L.) ?
• RAA increase from low pT to high pT

arXiv 0904.0439
STAR, PRC 80 (2009) 41902

• Jet quenching strong open charm suppression. A.
  Adil and I. Vitev, Phys. Lett. B649, 139 (2007),
  and I. Vitev private communication S. Wicks et
  al., Nucl. Phys. A784, 426 (2007), and W. A.
  Horowitz private communication.
• J/? is likely to be produced dominantly through
  CS states
• Contrast to AdS/CFT Hydro prediction (99 C.L.)
  H. Liu, K. Rajagopal and U.A. Wiedemann PRL 98,
  182301(2007)T. Gunji, J. Phys.G 35, 104137
  (2008)
• Formation time, gluon dissociation,
  recombination, B reproduces the trend
• X. Zhao and R. Rapp (2007), arXiv0712.2407.

• Z. Xus talk (Thursday, Quarkonia session)
  

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Direct photon - hadron correlations

• at a given zT, away side yield per ?0 trigger is
  significantly larger that the yield per direct ?
  trigger ? ?dir carries the total scattered
  momentum and ?0 from g/q jet fragmentation
• In AuAu collisions, path length, energy of
  parton, color charge dependence, jet conversion
  etc. plays roles
• gamma jet results are consistent with most
  theoretical calculations shown on the plot

IAA(ZT)D(ZT)AA/D(ZT)pp
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Full jet reconstruction in AA
New approach for assessment of jet
quenching Several different algorithms were
implemented - comparable jet X-sec in pp
collisions with published result - ratio is
suppressed for central AuAu relative to pp
? significant broadening of jet energy profile
in AuAu
Radius parameter defined in ? and ? space
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Ridge decreases with reaction plane (RP)
STAR Preliminary
Ridge drops when trigger particle moves away from
RP.
trigger fs
in-plane
out-of-plane
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Correlation Asymmetry
v2 syst.

• Jet is symmetric.
• Ridge is Asymmetric!
• Ridge may be due to
• jet-flow alignment.

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Ridge is structureless
R
x
STAR Preliminary
No prominent substructures in ridge.
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Summary

• Understand particle production mechanisms in pp,
  constrain FFs
• Kaon pT spectra up to high pT 15 GeV/c
• Fragmentation function measurements
• Characteristics of jet quenching in hot, dense
  medium
• RAA(ppbar) ? RAA(K) gt RAA(?)RAA(?) at pTgt6
  GeV/c, jet conversion
• challenging pQCD energy loss calculations
• J/psi RAA1 in CuCu collisions at pTgt5 GeV/c.
• Gamma-h correlations? golden probes to study jet
  quenching
• Full jet reconstruction? how jet energy is
  dispersed in the medium
• Ridge asymmetry and no structure observed ?
  challenging model calculations
• Thanks to the STAR
  Collaboration !

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BackUp
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Jet hadro-chemistry in AuAu and pp

• Model comparisons
• Need detailed modeling of enhanced parton
  splitting and jet conversion
• Expanding medium
• Improved fragmentation function, which our data
  will provide better constraints on.
• High pT K measurements in dAu, centrality
  dependence in AuAu and v2