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?

?