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Jet Correlations from PHENIX
• Focus entirely on A+A collisions• High-trigger pT correlations
– Can we do jet tomography?
• Low-trigger pT correlations– Away-side shape modification– RP dependence
• An outlook– Direct -h correlations, non-photonic e-h correlations
Nathan Grau, Columbia University, Nevis Labs
For the PHENIX Collaboration
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ConstructingJet Correlations
ddN
ddNC
d
dN
N mix
realpairs
trig /
/1
Mixed events – corrects pair acceptance
Hard scattering Resonance decays
(rad)
Elliptic flowTotal
C(
)
Sum over all events jets measured on a statistical basis
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Jet Quenching
• Single particle suppression pattern persists to 20 GeV• Moderate pT jets are suppressed• Due to energy loss of partons in the medium
Pedestal&flow subtracted
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Away-Side Jet in Au+Au!
• C() strength ~ S/B of jets• Red and blue lines are the uncertainty in v2.• Jets seen above the background for trigger >5 GeV/c and
associated >2 GeV/c
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Clear Away Side in Cu+Cu!
• Larger jet S/B in central Cu+Cu than central Au+Au
• v2 modulation is smaller as well
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Lack of Away-Side Broadening
8 < pT(trig) < 15 GeV/c
Widths do not change between p+p and Au+Au?!?
Trigger 5-10 GeV/c
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Expected Broadening of Away Side
Able to fit IAA from STAR.Red – gluons from energy loss.
Black – scattering of parent partons
I. Vitev hep-ph/0501255
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Away Side Yield Suppression
• Away-side yield is suppressed?!?
• What mechanism can suppress yields without broadening them?– Tangential jets?
– Punch through?
8 < pT(trig) < 15 GeV/c
D. Magestro QM2005
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Punch-through Events (I)
• Monte Carlo includes radial expansion reducing the effect of E ~ L2
• Non-zero probability to lose no energy
• Does the away side carry away any information from the interior of the collision zone?
Production vertices of events with trigger > 8 GeV
Red circles indicate an associated hadron (> 4 GeV) suffering no E-loss
T. Renk hep-ph/0602045
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Punch-through Events (II)
• Yield suppression sensitive to the probability of punch-through
• Lower pT pairs are apparently more sensitive to energy loss…
Comparison of MC to STAR away-side yields.
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Lower pT Correlations
• h-h Correlations in Au+Au (upper plots)– C() strength ~ jet S/B– Few % S/B at lowest pT Correlations.
• h-h Correlations with background subtracted (lower plots)
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Different Colliding Systems and Energies
Au+Au @ 200 GeV
Cu+Cu @ 200 GeV
Au+Au @ 62.4 GeV
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Parameterize the Away-Side Shape
trigg
assoc
D
Dassoc
Parameterize the away-side shape as a double Gaussian that are offset symmetrically around = by fit parameter D.
Could be a “bent” jet or a mach/ Cherenkov cone
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Au+Au Reaction Plane Dependence (I)
Look at 4th bin since it has the smallest v2.
Dip exists at most central before substraction!
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Au+Au Reaction Plane Dependence (II)
Know v2 depending on triggers RP orientation.
Shape independent of RP orientation
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Au+Au Reaction Plane Dependence At Higher pT
• No hint of a volcano shape in any RP bin
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For the future: Direct -h
• Direct photons not suppressed in the medium.• Much less “trigger bias” i.e. less biased toward skin emission• Photon measures jet energy measured away-side D(z) modification
Hadrons
gqq
qqg
PRL 94 232301 (2005)
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Inclusive -h Correlations in Au+Au
C
(
C(
: 5-10 GeV/ch: 1-2 GeV/c
Comparison with 0 triggered data necessary to extract direct photon correlations.
: 5-10 GeV/ch: 3-5 GeV/c
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Comparison of - and 0- Triggered Widths
Near-side widths are consistent between -triggered and 0-triggered.
Dominant inclusive photon correlation is decay from jet fragments
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-h Near Side Yields
PRL 94 232301 (2005)
~50% direct photons above 5 GeV/c in the most central.
Also seen in -triggered near side yield ratio to 0 -triggered yield.
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For the future: Non-Photonic e-h
Use jet correlations to further understand heavy quark energy loss.
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Summary and Conclusions
• High-pT triggered correlations show– Au+Au away-side that is not broadened– A suppressed yield consistent with punch-through jets.– What is learned from these correlations then?
• Low-pT triggered correlations show a strongly modified away-side shape– independent of system size and collision energy– Independent of trigger orientation to the RP
• Still left to do with current data– Further RP studies: Can we show E ~ L2,Ln?– Direct -h: D(z) modification– e-h Correlations: Heavy quark energy loss
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