Azimuthal Anisotropy at high p T in Au+Au Collisions at PHENIX
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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
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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
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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.
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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
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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
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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():
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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
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Run4 Results
Submitted for publication: arXiv:0903.4886
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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;
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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
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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 ……
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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.
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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
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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
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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)
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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
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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.
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Backup
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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
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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: