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Xiaoyang Gong for PHENIX Collaboration

Collision energy dependence of flow results in Au+Au collisions at = 7.7-200 GeV from

PHENIX

Phase diagram 2

A central goal in nuclear physics is to map out the QCD phase diagram.

RHIC has embarked an beam energy scan (BES) program to:

a) Locate the QGP-Hadron Gas phase boundary and critical point.

b) Obtain properties of nuclear matter in each phase.

RHIC experiments at 200GeV beam energy showed that QGP is created and cools down to hadron gas via a crossover transition.

Alver, Roland, Phys.Rev.C81, 054905

Probe Phase Diagram 3

From Yadav, WWND2011

What probes do we have to study nuclear matter created at RHIC?

SpectraHBTFlow observablesParticle azimuthal correlation, jetFluctuations

Focus of this talk

Eccentricity of initial geometry leads to a non-trivial profile of particle azimuthal distribution (dN/dφ).

Characterized by Fourier Coefficients vn.

Why Flow Measurement? 4

Phys.Rev.Lett.97, 152303 (2006)

Flow measurement at each of the beam energies could help us answer the following questions:

- At what energy flow at partonic level is turned off?

- The initial geometry fluctuations of nuclear matter created at different energies?

- Specific viscosity (η/s) at these beam energies?

Precise and Robust Measurement 5

Reaction plane detectorRXNINN (1.5<||<2.8)RXNOUT (1.0<||<1.5)

Muon piston CalorimeterMPC (3.1<||<3.9)

Beam-beam counterBBC (3.1<||<3.9)

RXNRXN

BBC/MPC BBC/MPC

Forward detectors at different η:

Measurements with different forward detectors help us control systematics

Independent Measurements 6

Gong and Ark use event-plane method: reconstruct event planes in the forward detectors; measure central arm particle azimuthal distributions relative to event plane.

Gu uses long-range correlation method: Fourier decomposition of correlation functions built with one particle from central arm and the other from forward detectors.

Remarkable agreements between two methods!

Charge Hadron v2: 39, 62 and 200GeV 7

v2 show saturation for beam energy 39-200GeV.

Preliminary, STAR, PHENIX and E895 data

v2

v2’s at 7.7GeV are significantly lower than those at 39, 62 and 200GeV

Excitation Function 8

Saturation of v2: indicate a Softening EOS?A decreasing trend of v2 below 39GeV.

Higher Order Harmonics: v3 and v49

Significant attention has been given to the higher order harmonics recently.

Measurements at 200GeV and higher beam energies show that higher order harmonics could provide additional constraints on initial geometry models and specific viscosity.

Do v3 and v4 saturate at 62 and 39GeV as v2 did?

Charge Hadron vn(Ψn): 62GeV 10

Sizable v3 and v4 signals compared to v2.

vn(Ψn)

v3 does not change with centrality. v4 increases with centrality slightly.

Charge Hadron vn(Ψn): 39GeV 11

vn(Ψn)

Sizable v3 and v4 signals as well.

Beam Energy Dependence of v3(Ψ3) 12

v3(Ψ3)

v3(Ψ3)

PHENIX Preliminary

Beam Energy Dependence of v4(Ψ4) 13

v4(Ψ4) for lower energies are smaller; still saturate within systematic errors.

v4(Ψ4)

v4(Ψ4)

PHENIX Preliminary

Saturation at LHC energy 14

vn(Ψn) vn(Ψn)

vn has been measured up to 6th order on experiments at LHC. How do vn measured at RHIC compared to those at LHC?

V3 and v4 saturate above 39GeV, up to LHC energy.

Identified Charge Hadron v215

Does quark number scaling hold at 62 and 39GeV?

Generally scales; small discrepancies at 0.4 GeV

v2 at Intermediate pT16

Phys. Rev. Lett. 105, 142301 (2010)

So far we focused on low pT (<3GeV) region, what about v2 at higher pT?

Saturation observed at intermediate pT (3 to 6GeV) region as well, where v2 represents the combined effect of hydro-dynamics and jet energy-loss.

Summary 17

v2, v3 and v4 are measured in 39, 62 and 200GeV, and compared to Atlas measurement. v2’s of pion, kaon, (anti)proton show scaling down to 39GeV. v2 saturates in intermediate pT as well as show by neutral pion measurement.

Preliminary, STAR, PHENIX and E895 data

Smooth dropping of v2 is observed below 39GeV.

Data taken at 19.6GeV this year would help us check the “gap” in the transition region.

vn(Ψn)

?

These observations suggest similar initial geometry fluctuations and dynamic evolution of nuclear matter above 39GeV.

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Backup

v4(Ψ2)

Since Ψ2 and Ψ4 are correlated, we observe sizable v4(Ψ2) (about half of v4(Ψ4)).

Beam Energy Dependence of v4(Ψ2) 19

V3 20

PID v2 saturation 21

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62GeV