v2 and v4 centrality, pt and particletype dependence in Au Au collisions at RHIC

1
v2 and v4 centrality, pt and particle-type
dependence in AuAu collisions at RHIC
Yuting Bai for
the STAR Collaboration
Cern Heavy Ion Forum, Dec. 13, 2006
2
Outline

• Introduction
• v2
• v4
• v4/v22
• Conclusion

3
Anisotropic Flow

• Anisotropic flow azimuthal correlation with the
  reaction plane
• established early, self-quenching, therefore
  sensitive to the early stage of the collisions

4
Charged particle v2 as function of pt at 200GeV
and 62GeV
v24 v2 from 4-particle cumulant method.

• Charged particle v2 from four particle cumulant
  are measured up to 10 GeV at 200GeV.
• For AuAu at 200 GeV still significant v2 above 6
  GeV/c

5
Charged particle v2 as function of pt at 200GeV
and 62GeV

• 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.

6
Charged particle v2 as function of pseudorapidity
at 200GeV and 62GeV

• v2 increases from 62 to 200 GeV

7
v2200/v262 as function of pseudorapidity at
200GeV and 62GeV

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

8
Charged particle v2 as a function of h-ybeam
at 200GeV and 62GeV
Only particles with positive h are shown

• Longitudinal scaling approximately holds

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!

event plane method
10
Centrality dependence NQ scaling
Star Preliminary

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

11
NQ scaling at 62.4GeV
minbias data (0-80)

• At 62.4 and 200 GeV the same scaling is observed!

12
Higher Harmonics
Peter Kolb, PRC 68, 031902

• Higher harmonics are expected to be present. For
  smooth azimuthal distributions they will be
  small, vn v2n/2
• v4 /v22 a probe of ideal hydro behavior and
  related to degree of thermalization!

R.S.Bhalerao et.al PLB 627,49 Borghini and
Ollitrault, arXivnucl-th/0506045
13
Charged particle v4 as function of pt at 200GeV
and 62GeV
Star Preliminary
Star Preliminary
-1.3 lt eta lt 1.3
Relative to the 2nd order event plane

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

14
Charge particle v4 as function of pseudorapidity
at 200GeV and 62GeV

• As for v2, v4 increases from 62 to 200 GeV

15
Charged particle v4 as function of h-ybeam at
200GeV and 62GeV

• Same as v2, for v4 longitudinal scaling
  approximately holds

16
v4 systematic uncertainty estimate

• Uncertainties on ltv4gt are small, however they
  quickly become significant at larger pt

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

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/v22 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

19
v4/v22 for charged particle as a function of pt
at 200GeV and 62GeV
Star Preliminary
20
v4/v22 for charged particles as function of
pseudorapidity at 200GeV and 62GeV
Star Preliminary
21
non-flow effect on v4/v22
For v4/v22