Azimuthal AnisotropyAzimuthal Anisotropy at high p at high pTT in Au+Au in Au+Au Collisions at PHENIXCollisions at PHENIX

Rui WeiRui WeiNuclear Chemistry GroupNuclear Chemistry Group

Stony Brook UniversityStony Brook University

22

Outline

Motivation:• Why we are interested in high pT

• Why azimuthal anisotropy Experimental approach:

• How to measure the anisotropy Results discussion

• v2(pT, centrality)• RAA(pT, centrality)• Comparisons to model calculations

Summary

33

Why high pT

Domain of hard scattering process• Large momentum transfer Q2 (~pT

2);• Cross-sections are factorizable.

p+p as a good reference• Fragment into QCD-vacuum;• pQCD is applicable;• Data and calculation agree well;

Au+Au• Occurs early in the collisions;• Probe the hot and dense medium;

PHENIX, PRD76(2007)051006(R)

Observed deviations from the reference measurements can be attributed to the medium.

44

RAA – nuclear modification factor

• RAA ~ 0.2 for pT > 5.0 GeV/c

sscattering NN indep.for n ExpectatioAAin yield Measured)(

1)( 2

2

TAA

TppAB

TevtsTAA

pR

dydpdTdydpNdNpR

Au+Au 0 + X (central)

Strong suppression is observed.

RA

A

1

00 2010

pT (GeV/c)

0

55

arXiv:0903.4886

Why azimuthal anisotropy

Source of energy loss• Radiative• Collisional• Study the path length dependence

Discriminating power of RAA is not enough:• All jet quenching models work well.• But with large discrepancy of extracted transport coefficient q-hat:

HT: 2.3 GeV2/fm AMY: 4.1 GeV2/fm ASW: 10 GeV2/fm

S.Bass arXiv:0808.0908

Differential angular measurements of RAA:• Run4 results• Help to discriminate between models• High pT: limited by statistics

66

Experimental Measurements

Azimuthal anisotropy (v2):• Particle yields w.r.t. the reaction plane• Corrected for R.P. resolution 0s in this analysis;

Relative yields corrected by R.P resolution

30-40%

PHENIX Preliminary

MultiplyBy inclusive

RAA

RAA():

77

Reaction Plane Detectors

RXNout is biased by jets;• Closer to central arm.

MPC is used:• Same rapidity window as BBC;• ~40% better resolution;• In addition with 4 times more statistics!

Run4: BBC (3<||<4); Run7:

• MPC (3.1<||<3.9)• RXNin (1.5<||<2.8)• RXNout (1.0<||<1.5)

Provide better R.P. resolution

88

Run4 Results

Submitted for publication: arXiv:0903.4886

99

Preliminary Run7 0 v2 results

We extended pT range up to 13GeV/c in each centrality bin; Sizeable v2 at high pT is observed, and is relatively flat;

1010

RAA(pT) results

In-plane

Out-of-plane

Grey bands: Error in RAA

0

/2

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Comparisons to model calculations

0

/2

Implication: large q-hat for the medium?Calculation from S.Bass et al arXiv:0808.0908

1212

Challenge for theoretical calculations

Comparisons in other centralities needed.

The models fail, yet reproduce RAA vs pt• Need stronger variation of Eloss on paths length, or• Sharper initial spatial distribution of energy density, or• More rapid variation of q with , or ……

1313

v2 Comparisons to Geometric Models

V. Pantuev: arXiv:hep-ph/0506095• Corona effect, L ~ 2fm;

J.Liao and E.Shuryak: arXiv:0810.4116

• Stronger jet quenching at near-Tc region;

physics beyond pQCD?...

E.Shuryak: PRC 66 027902 (2002)

• Geometric limit: v2(high pT) < v2max(b)

• Too large for a pure “jet quenching” A.Drees, H.D.Feng, J.Jia: Phys.Rev.C71:034909,2005

• Jet absorption proportional to matter density;• Can’t reproduce the large v2.

1414

E-loss: not limited to single particle observable

Two particle correlations• Gamma-jet• R.P. dependent of jet correlations

IN-PLANE MID-PLANE OUT-OF-PLANE

W. Holzmann, QM09

1515

Out-of-plane vs. in-plane

• Out-of-plane nearly constant for Npart>100;• Geometric dependences are different for two orientations.

0

/2

pT

NPart

RA

A

in-plane

out-of-plane

1616

Similar RAA(pT) and v2(pT)

No pT dependence at high pT; Centrality dependence is also similar; Imply a correlation.

MinBias 0-10%

20-30% 40-50%

60-70% 80-92%

PRL 101, 232301 (2008)

1717

RAA(pT) vs. v2

Look at 0-60%, pT>1 GeV/c Transition from soft to hard regimes?

RAA

v2

Acta Phys.Hung.A27 (2006): Horowitz, QM05

Cu+Cu

• Different behavior.

• At low pT

• Flow carries initial geometry info.

• At high pT

• In central, the asymmetry is small.

• In peripheral, the jet quenching is small.

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pT dependence of v2(Npart)

How is v2 related to the initial geometry?• Low pT: saturate;• High pT: more linear;

Charged hadron results

1919

Summary

Presented detailed measurements of RAA and v2:• With enhanced statistics and improved reaction plane resolution;

Measurements indicate:• v2 is sizeable and relatively flat at high pT;• RAA show strong angular dependence relative to the reaction plane.

Initial additional constraints obtained via RAA and anisotropy using 20-30% centrality data;

Implication: large q-hat value for the medium?

Comparisons with geometrically inspired models.

Backup

2121

Reaction Plane Measurement with PHENIX

Reaction Plane Detectorplastic scintillators @ 38<|z|

<40cm12 segments in 2 segments in

• 1.0 < || < 1.5• 1.5 < || < 2.8

Pb converterRun 7+

Beam-Beam Counters• Quartz Cherenkov

radiators• 64 elements in 3

rings• 3.0 < || < 4.0• All Runs

Muon Piston Calorimeter

• PbWO4 PHOS crystals

• 192 towers• 3.1 < || < 3.7• Run 6+

Multiple overlapping and complementary measurements

2222

High pT v2

v2 measurement:• Low pT: hydrodynamics;• Intermediate pT: recombination + hydro;• High pT: jet suppression?• Study their relations with the initial

geometry.

PRL. 91, 182301 (2003)

x

y

ψR

φ=Φ-ΨRDecompose into Fourier basis: