v2 and v4 centrality, pt and particle-type dependence in Au+Au collisions at RHIC

Yuting Bai

for the STAR Collaboration

Yuting Bai 2

Outline

Introduction v2

v4

v4/v2

2

Conclusion

Yuting Bai 3

Anisotropic Flow

Anisotropic flow ≡ azimuthal correlation with the reaction plane

established early, self-quenching, therefore sensitive to the early stage of the collisions

1

2

3

3

cos),(21dd

d

2

1

pd

d

nrtn

tt

nypvypp

NNE

rn nv cos

Yuting Bai 4

Charged particle v2 as function of pt at 200GeV and 62GeV

Charged particle v2 from four particle cumulant are measured up to ~ 10 GeV at 200GeV. For Au+Au at 200 GeV still significant v2 above 6

GeV/c

-1.3 < < 1.3

Star Preliminary Star Preliminary

v2{4}: v2 from 4-particle cumulant method.

Yuting Bai 5

The centrality dependence of v2 changes from low-pt to intermediate pt.

At intermediate pt the maximum v2 is for the 30-40% centrality bin around 3 GeV/c.

Charged particle v2 as function of pt at 200GeV and 62GeV

Star Preliminary Star Preliminary

Yuting Bai 6

Charged particle v2 as function of pseudorapidity at 200GeV and 62GeV

Star Preliminary

v2 increases from 62 to 200 GeV

Yuting Bai 7

The increase in v2 from 62 GeV to 200 GeV is larger at forward rapidity could be understood as a result of v2 ~ dN/d

v2{200}/v2{62} as function of pseudorapidity at 200GeV and 62GeV

Star Preliminary

Yuting Bai 8

Charged particle v2 as a function of -ybeam at 200GeV and 62GeV

Longitudinal scaling approximately holds

Star Preliminary Only particles with positive are shown

Yuting Bai 9

Centrality dependence: (mT – m) scaling

At low-pt mT-scaling: indicative for a common velocity for the different particles At intermediate pt meson-baryon grouping: indicative for coalescence mechanism mT-scaling and baryon meson grouping holds for all centralities!

Star Preliminary

event plane method

Yuting Bai 10

Centrality dependence: NQ scaling

NQ scaling holds for all centralities. is systematically lower than other particles in central collisions.

Star Preliminary

Yuting Bai 11

Star PreliminaryStar Preliminary

NQ scaling at 62.4GeV

At 62.4 and 200 GeV the same scaling is observed!

minbias data (0-80%)

Yuting Bai 12

Higher Harmonics

Higher harmonics are expected to be present. For smooth azimuthal distributions they will be small, vn ~ v2

n/2

v4 /v22 a probe of ideal hydro behavior and related to degree

of thermalization!

Peter Kolb, PRC 68, 031902

R.S.Bhalerao et.al PLB 627,49; Borghini and Ollitrault, arXiv:nucl-th/0506045

Yuting Bai 13

Charged particle v4 as function of pt at 200GeV and 62GeV

Charged particle v4 are measured up to ~ 7 GeV at 200GeV.

Star PreliminaryStar Preliminary-1.3 < eta < 1.3

Relative to the 2nd order event plane

Yuting Bai 14

As for v2, v4 increases from 62 to 200 GeV

Charge particle v4 as function of

pseudorapidity at 200GeV and 62GeV Star Preliminary

Yuting Bai 15

Same as v2, for v4 longitudinal scaling approximately holds

Charged particle v4 as function of -ybeam at

200GeV and 62GeV Star Preliminary

Yuting Bai 16

v4 systematic uncertainty estimate

Uncertainties on <v4> are small, however they quickly become significant at larger pt

2

24*

,2*

,2,4

4

)()(

nscorrelatio k)j,(i, particle 3 from

vptvuuptu

v

kji

)(* nonflow

flowby correlated are

k and i and nonflowby correlated

are j and i if scontribute nonflow

222 ptvvg

)}(4{)}(2{~ 22

222 ptvptvg

vvvv ptptpt

2

2

2

2

2

2)}(4{*))}(4{)}(2{(

Yuting Bai 17

v4/v22 for charged particles at 200GeV

v4 /v22 a detailed probe of ideal hydro behavior and related to the degree

of thermalization! Data points are above the model predictions, however due to the

systematic uncertainty from non-flow we can not exclude the models yet

Star Preliminary

Yuting Bai 18

Conclusions v2 from four particle cumulant is measured up to

10 GeV/c Still significant v2 observed above 6 GeV/c

v2 for identified particles shows mT scaling at low-pt and NQ scaling at intermediate pt

For all centralities The energy dependence of v2 and v4 is

approximately described by longitudinal scaling The observed ratio of v4/v2

2 is above the ideal hydro predictions and close to AMPT, however the systematic uncertainties from non-flow do not allow us to contradict ideal hydrodynamics

Yuting Bai 19

v4/v22 for charged particle as a function

of pt at 200GeV and 62GeVStar Preliminary

Yuting Bai 20

v4/v22 for charged particles as function of

pseudorapidity at 200GeV and 62GeVStar Preliminary

Yuting Bai 21

Systematic errors are shown at mid-rapidity only. At forward rapidity, the non-flow effects are expected to be small.

at mid-rapidity, the ratios are above 1, which is compatible with those at forward rapidity .

v4/v22 for charged particles as a function

of pseudorapidity at 200GeV

Star Preliminary

Yuting Bai 22

non-flow effect on v4/v22

)(

)())}(4{)}(2{(2

22

2

2

2

2

2

pt

ptptpt

vvvvv

For v4/v22 :