2011/03/23 Moriond QCD 2011 John Chin-Hao Chen 1

The story of v3

John Chin-Hao Chen (陳勁豪 )for PHENIX Collaboration

Stony Brook UniversityMoriond QCD2011/03/23

2011/03/23 Moriond QCD 2011 John Chin-Hao Chen 2

outline

• What is v3?

• How to measure v3?

• How do theorist think of v3?

• Does v3 explains the jet shape modification (ridge and shoulder)?

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vn: particle anisotropy

• Spatial distribution of colliding area is “almond” like due to overlap of two colliding nuclei.

• dN/d(-) =N0((1+2vncosn(-)))

• v2 = elliptic flow

• If nuclei is perfect spherical-> no vodd

• With some initial state fluctuation -> finite vodd?

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Glauber initial state

• The nuclear is not perfect in shape

• Nucleon distribution is not smooth

• Azimuthal symmetry no longer holds

• vodd is possible

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2-D correlations

shoulder ridge

rad

Peripheral Au+Au/pp Central Au+Au

Both near and away sideare modified!

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v3, reason for ridge and shoulder?

• Ridge sits at ~ 0, shoulder sits at ~2/3, 4/3– A 3-peak structure!

• v3 (Fourier Coefficient of the cos3term) gives a natural 3-peak structure

• Is v3 the explanation?

• Need to measure v3 to answer this question!

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How do we measure v3?

• Reaction plane method– Use forward detector to determine the n-th

reaction plane

• Two particle correlation method– No need to determine the reaction plane– central-central two particle correlations

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S. Esumi, WWND2011

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Measuring vn with n

• Use the forward detector to determine the nth event plane, n

• Measure vn respect to n and correct with reaction plane resolution n

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S. Esumi, WWND2011

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vn from two particle correlations

• Standard v2(v4): single particle vs. reaction plane dN/d(

• Can also measure vn via two particle correlation– Central-central correlation (0.3<||<0.7)– PHENIX: Phys. Rev. Lett. 89, 212301 (2002)

– dNAB/d= N(1+ (2Cncos(n))), Cn = vnAvn

B

• the two particles are in the same event, therefore share the same reaction plane

• When pTA = pT

B, vn = sqrt(Cn)

• With low partner pT (below 1 GeV), the jet contribution can be ignored, but not at high pT

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v2{2p}, v3{2p} from two particle correlations

• v2{2p} agrees with previous PHENIX measurements at low pT

• v3{2p}– Nonzero– Increases with pT (NB: may have non-flow effects in this method)– Increases with centrality

v 2{2

p},

v 3{2

p},

Dash line is PHENIX v2 measured by event planePhys. Rev. Lett. 105, 062301 (2010)

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• 2-particle (small ) v3 higher than reaction plane (large v3

• should expect non-flow contribution i.e. jets

Compare with v3 measured by 3

RP2P

v3

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Compare with Hydro calculation

• Large gap measurement (bulk only) agrees well with hydro prediction!

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What about non-flow in v3?

• Use jets in p+p to calibrate!• Do a Fourier analysis of the per trigger yield jet

function – JF = Cn cos(n)

– For Au+Au: combinatorial background “b0(1+2v2

trigv2partcos2)” removed via ZYAM

– ZYAM will not change any Fourier coefficients, except C0 and C2

• Various centrality and partner pT bins for initial insights into bulk vs. jet contributions

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Baseline comparison

• Dijet (pp) and away-side suppressed dijet– pp tells us the pure jet contribution– pp nearside only: the awayside jet is fully suppressed

• The jets in AuAu (nearside jet + “head”) should fall in between.

• Fourier strength beyond this is not from the jets.– Jet-bulk contribution!

• v2 of bulk (background) flow subtracted when making the jet function

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Fourier Spectra of Jet Function

v3 from jet

v3 from jet+bulk+jet-medium int.?

•No significant contribution above c4

•Removing the awayside pp enhances the codd terms

•The c3 in AuAu has contributions from both jet and bulk!

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summary

• v2, v3 and v4 are measured with n and two particle correlations.

• v3 measured by two particle correlations (small gap) are consistent with but larger than reaction plane method (large gap)

• v3 from reaction plane method agrees with hydro prediction

• The third Fourier coefficient in jet function is significantly enhanced in central AuAu collisions due to the v3 from bulk, but also have some contributions from the jet