Hard Probes and Heavy Flavor from STAR

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Hard Probes and Heavy Flavor from STAR

• Saskia Mioduszewski
• for the STAR Collaboration
• Texas AM University
• Rencontres de Moriond QCD and High Energy
  Interactions
• 14 March, 2008

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Why Hard Probes?

• Only photons decouple from medium upon creation
• Large-mass quarks provide particularly good probe
  of medium produced
• Created early in the collision
• mc 1.3 GeV, mb 4.8 GeV gtgt Tc, LQCD ? less
  affected than light quarks
• Perhaps more direct connection to transport
  properties of medium
• What Questions Can be Addressed via Hard Probes?
• g-jet true (modified) fragmentation function
• Open Charm/Beauty energy loss mechanism, degree
  of thermalization
• Quarkonium deconfinement (dissociation in QGP),
  degree of thermalization

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One of the most surprising results from RHIC

• Heavy flavor suppression as large as for light
  quarks
• No dependence of energy loss on flavor
• Do we understand energy loss mechanism?
• Where is Beauty contribution?

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Quark vs. Gluon Energy Loss
Baryon meson RAA
Mechanism of energy loss Medium-induced gluon
radiation
Effect of color charge

• Factor 9/4 Color effects not observed up to pT
  12 GeV/c
• - Not sensitive?
• - In-medium conversions, q??g? (W. Liu, R.J.
  Fries, arXiv0801.0453)
• - Energy loss mechanism not understood

Theory X.-N. Wang, PRC 70 (2004) 031901
Data PRL 97 (2006) 152301
PLB 655 (2007) 104
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From Single-Particle to 2-Particle Correlations
Di-jets (hadron-hadron correlations)
Single inclusive hadrons
Suppression quantified by IAA Jet-assoc.
YieldAA/Jet-assoc. Yieldpp Hadrons associated
with high-pT trigger particle ? More differential
probe of energy loss Surface bias reduced, but
not removed
Suppression quantified by RAA
YieldAA/(Yieldpp ltNbinarygtpp) Single particle
is leading hadron of jet ? Probe of density of
medium, but Strong surface bias for trigger
particle
Trigger
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Trigger Biases
Di-jets (hadron-hadron correlations)
Single inclusive hadrons
Renk and Eskola, hep-ph/0610059
Renk and Eskola, hep-ph/0610059
Trigger particle
Trigger particle

• Photon-jet measurement is, in principle,
  sensitive to full medium
• True measure of the Energy (no energy loss for
  direct photon)

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?-Jet Golden Probe of QCD Energy Loss
Wang et al., Phys.Rev.Lett. 77 (1996) 231-234
?
?
q
g
q
QCD analog of Compton Scattering
h

• ? emerges unscathed from the medium
• - This probe is valuable for comparison with
  di-hadron correlations
• - Full reconstructed kinematics real
  fragmentation function D(z)

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Jet Suppression measured via direct photon
trigger
T. Renk, PRC74, 034906
Theoretical calculation showing sensitivity to
medium
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First measure of away-side IAA for g-h
A. Hamed, QM2008
Ejet E? E trig
Good agreement between theory and measurement
T. Renk and K. Eskola PRC75054910,2007
Suppression similar level to inclusives in
central collisions
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Away-side Yields Relative to Peripheral AuAu
A. Hamed, QM2008
Peripheral AuAu pp vacuum
Icp of ?-jet exhibits same suppression on the
away-side yield per trigger of the associated
particles (3-8GeV/c).
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One of the most surprising results from RHIC

• Heavy flavor suppression as large as for light
  quarks
• No dependence of energy loss on flavor
• Do we understand energy loss mechanism?
• Where is Beauty contribution?

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Electron-tagged correlations to obtain bottom
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

A. Mischke, QM 2008
heavy quark production
???0
????
flavor creation gluon splitting/fragmentation
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Heavy quark production in pp collisions
e-D0 correlation agree with e-h results

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

A. Mischke, S. Sakai, G. Wang, QM2008
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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)
Two Component Approach X. Zhao and R. Rapp,
hep-ph/07122407
Ads/CFT Calculation of Survival
J/Y Production in pp collisions
Most models expect a decrease in RAA as
function of pT
H. Liu, K. Rajagopal and U.A. Wiedemann PRL 98,
182301(2007) and hep-ph/0607062
Next step the ? - almost there
Z. Tang, QM2008
Z. Tang Session XVII, D. Das Session XXII
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Heavy Quarkonium Production (and Survival)

• Data consistent with no suppression at
• high pT RAA(pT gt 5 GeV/c) 0.9 0.2
• While at Low-pT RAA 0.50.6 (PHENIX)?
• Indicates RAA increase from low pT to
• high pT
• Most models expect a decrease RAA at
• high pT (not including bottom decays)
• Two Component Approach
• X. Zhao and R. Rapp, hep-ph/07122407
• AdS/CFT
• H. Liu, K. Rajagopal and U.A. Wiedemann,
• PRL 98, 182301(2007) and hep-ph/0607062

J/Y in CuCu Collisions at RHIC Z. Tang, QM2008
Contribution from beauty decays - better agreement
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Conclusions

• Surprise at RHIC heavy-quark energy loss does
  not follow expectation Do we really understand
  energy loss mechanism?
• Exploring di-jet and photon-jet measurements to
  constrain energy loss mechanism
• Beauty contribution to heavy flavor measurements
  is 50 at pT5 GeV/c, indicating that bottom
  must be suppressed as well
• J/Y not suppressed at high pT, contrary to
  expectation from theoretical calculation if no
  contribution from Beauty decays
• Need direct measure of Charm/Beauty up to high pT
  will be possible with planned upgrades

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Extra Slides
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Elliptic flow v2 NPE from HF decays
PHENIX Run4
PRL, 98, 172301 (2007)
Non-zero elliptic flow for electron from heavy
flavor decays ? indicates non-zero D v2, partonic
level collective motion. Strongly interact with
the dense medium at early stage of HI
collisions. Light flavor thermalization.
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J/? hadron correlations in pp
1) no near side correlation 2) strong
near side correlation
Z. Tang, QM2008
No near side correlation seen!
Away side consistent with leading charged
hadron correlations Near side consistent
with no associated hadron production
B?J/? not a dominant contributor to inclusive J/?
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Triggering on Di-Jets
T1 pTgt5 GeV/c, T2 pTgt4 GeV/c, A pTgt1.5 GeV/c
jet-axis trigger (T2)
primary trigger (T1)

• Di-jets are suppressed.
• Once select di-jets, away-side associated
  particles NOT suppressed.
• Shapes of near- and away-sides similar.
• Central AuAu dAu.

O. Barannikova, QM2008
No energy loss for triggered di-jets! Tangential
di-jets (or punch-through without interactions).
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Heavy quark production in pp collisions
A. Mischke, S. Sakai, G. Wang, QM2008

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