Kirill Filimonov, ISMD 2002, Alushta 1
Kirill Filimonov
Lawrence Berkeley National Laboratory
Anisotropy and high pT hadrons in Au+Au collisions at RHIC
• Introduction• Inclusive spectra• Jets and dijets• Azimuthal anisotropy at high pT
Kirill Filimonov, ISMD 2002, Alushta 2
Jets in heavy ion collisions
e+e- qqbar (OPAL@LEP)
p+p jet+jet (STAR@RHIC)
Au+Au ??? (STAR@RHIC)
What Can We See in Au+Au? • Leading particles• Azimuthal correlations
Kirill Filimonov, ISMD 2002, Alushta 3
Leading Particle Suppression
ddpdT
ddpNdpRT
NNAA
TAA
TAA //)( 2
2
leadingparticle Jets modified in heavy ion
collisions?-Leading particle suppression already observed in Au+Au at 130 GeV
Nuclear Modification Factor:
Glauber Model
Partonic Energy loss in high density matter
hadrons
q
q
hadrons
leading particle
hadrons
hadronsleadingparticle suppressed
leading particle suppressed
q
q
Kirill Filimonov, ISMD 2002, Alushta 4
High pT hadrons: Au+Au at RHIC
Preliminary sNN = 200 GeV
• Excellent quality data from the experiments
Kirill Filimonov, ISMD 2002, Alushta 5
Hadron suppression: Au+Au at 200 GeV
Preliminary sNN = 200 GeV
PHENIX preliminary
QM’02 prelim. data: suppression of factor 4-5 persists to pT=12 GeV/c
PHENIX peripheral and central over measured p+p
STAR charged hadrons: central/peripheral
Kirill Filimonov, ISMD 2002, Alushta 6
Two-particle correlations at high pT
),()(11)(2 NdefficiencyN
Ctrigger
• Jet corex0.5 x 0.5 look at near-side correlations (~0) of high pT hadron
pairs
• Complication: elliptic flow
• high pT hadrons correlated with the reaction plane orientation also correlated with each other (~v2
2)
• but elliptic flow has long range correlation ( >> 0.5)
• Solution: compare azimuthal correlation functions for and
Kirill Filimonov, ISMD 2002, Alushta 7
Direct evidence for jets
),()(11)(2 NdefficiencyN
Ctrigger
< 0.5 > 0.5
Azimuthal correlation function:• Trigger particle pT
trig> 4 GeV/c• Associate tracks 2 < pT < pT
trig
Near-side correlation shows jet-like signal in central Au+Au
Central Au+Au
N.B. Away-side jet contribution subtracted by construction, needs different method…
Kirill Filimonov, ISMD 2002, Alushta 8
Suppression of back-to-back pairs
Central Au + Au
Peripheral Au + Au
• Near-side well-described• Away-side suppression in central collisions
Away side jets are suppressed!
near side
away side
STAR Preliminary
C2(Au Au) C2(p p) A *(1 2v22 cos(2))
STAR Preliminary
STAR Preliminary
Kirill Filimonov, ISMD 2002, Alushta 9
Azimuthal anisotropy v2
22
22
xyxy )(tan,2cos 1
2x
y
pp
v
Coordinate space: initial asymmetry
Momentum space: final asymmetry
multiple collisions (pressure)
py
pxx
y distance of fast parton propogation
(energy loss)
Jet 1
Jet 2
Kirill Filimonov, ISMD 2002, Alushta 10
v2 predictions at high pT
M. Gyulassy, I. Vitev and X.N. WangPRL 86 (2001) 2537
The value of v2 at high pt sensitive to the initial gluon density
Saturation and decrease of v2 as a function of pt
at higher pt
pQCD inelastic energy loss + parameterized hydro component
Kirill Filimonov, ISMD 2002, Alushta 11
Comparison v2 (pT) with models (130 GeV)
• qualitative agreement with “jet-quenching” scenario
Adler et al., nucl-ex/0206006, STAR
Kirill Filimonov, ISMD 2002, Alushta 12
s dependence at high pT (200/130) STAR preliminaryRatio of spectra 200/130
Ratio of v2 200/130
• Inclusive spectra follow pQCD prediction (XN Wang)• minbias v2 has no energy dependence at pT>2 GeVsurface emission at high pT? (i.e. strong absorption)
Kirill Filimonov, ISMD 2002, Alushta 13
Centrality dependence of v2(pT)
• v2 saturates for pT>3 GeV/c for all centralities
• Indication of geometric origin?
(%)
PHENIX, preliminary STAR, preliminary
Kirill Filimonov, ISMD 2002, Alushta 14
Comparison with parton cascade
1) Does v2 saturate for all species?2) Will v2 decrease beyond pT=6 GeV/c?
D. Molnar
5x minijet multiplicity from HIJING
13x pQCD gggg cross section
Preliminary
Kirill Filimonov, ISMD 2002, Alushta 15
v2(pt) proposed scenario: flavor dependence
Baryon production by a non-perturbative mechanism (junctions or hydro)M. Gyulassy, I. Vitev, X.N. Wang and P. Huovinen, Phys. Lett. B 526 (2002) 301-308
Kirill Filimonov, ISMD 2002, Alushta 16
STAR Preliminary
v2 of identified hadrons
• Mesons and baryons show different trend at higher pT
• Qualitative agreement with the predictions
STAR Preliminary
PHENIX Preliminary
Negativespi-&K-,pbar
Kirill Filimonov, ISMD 2002, Alushta 17
v2(pT) up to 12 GeV/c (STAR)
• Finite v2 up to 12 GeV/c in mid-peripheral bin
• Decrease from saturation level for more central collisions
Kirill Filimonov, ISMD 2002, Alushta 18
Summary
• Jet fragmentation observed, agreement with pQCD• Strong suppression of inclusive yields• Suppression of back-to-back hadron pairs• Azimuthal anisotropy at high pT
large parton energy loss and surface emission?
What would large energy loss imply?•Partonic or hadronic energy loss?•Thermalization?
?
Top Related