1. PID v2 and v4 from Au+Au Collisions at √sNN = 200 GeV at RHIC
N. Li for the STAR Collaboration
Lawrence Berkeley National Laboratory, Berkeley
Institute of Particle Physics, Wuhan, China

2. Outline Motivation Analysis Results Summary
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3. Motivation Formation of QGP in high-energy nuclear collisions:
De-confinement
Collectivity
Local thermalization
Important questions
We study with dataset of highest statistics
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4. Anisotropy Parameters
spatial
space
anisotropy
Azimuthal correlation with
the reaction plane.
Built up in the early stage,
therefore supplies the
early information of matter
generated in the collision.
momentum
space
anisotropy
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5. Motivation (cont.) Study the PID dependence of v2 and v4.
Study Number-of-Quark scaling.
Range?
v4/v22 : a probe of ideal hydro behavior.
STAR: Phys. Rev. C 77 (2008) 54901
pQCD
ReCo & Coalescence
Hydro
R. S. Bhalerao et.al PLB 627, 49;
Borghini and Ollitrault, PLB 642, 227
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6. Anisotropy Parameter v2
STAR: Phys. Rev. C 77 (2008) 54901
How about the
higher order
anisotropic flow
such as v4?
Baryon and meson elliptic flow follow the number of
quark ( Nq ) scaling.
Indicates that partonic flow builds up at RHIC.
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7. Anisotropy Parameter v2 v4
STAR: Aihong Tang, Proc.
24th Winter Workshop on Nuclear Dynamics
Peter Kolb, PRC 68,
Hydro, Boltzmann calculations:
J. –Y. Ollitrault
v4 : 4th harmonic
If system reaches local thermal equilibrium, according to ideal hydro dynamic calculation, v4/v22 approaches 0.5 at high pT region.
Directly related to the degree of thermalization of the medium.
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8. Dataset and Cuts System: Au+Au collision Energy : sNN = 200 GeV
Event sample : ~60 M events
Year: 2007
Pseudorapidity range:
TPC : < η < 1
FTPC : < η < -2.5 (east)
2.5 < η < 4.0 (west)
Tracks used for TPC event plane:
No. of fit hits > 15
No. of fit hits/No. of possible hits >0.52
0.1 < pT < 2.0 GeV/c
| η | < 1.0
Tracks used for FTPC event plane:
6 =< No. of fit hits < 12
No. of fit hits/No. of possible hits > 0.52
0.1 < pT < 2.0 GeV/c
2.5< | η | < 4.0
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9. TPC Event Plane 2nd harmonic event plane (a) (c) (b)
STAR preliminary
(a)
2nd harmonic event plane
Event plane angle (Rad)
(c)
STAR preliminary
(b)
Detector bias is removed by applying
phi weights to the tracks.
Phi weights are generated by
inverting the normalized phi
distributions of detected tracks for a
large event sample.
Na Li th Winter Workshop on Nuclear Dynamics

10. FTPC Event Plane The event plane distribution is
J.Barrette et al. Phys. Rev. C56 (1997)3254
Phi weight + Shift
Phi weight
Event plane angle (Rad)
STAR preliminary
The event plane distribution is
not flat after phi weight
correction due to several
acceptance effect of FTPC.
Add additional shift correction.
Large η gap is used to reduce
the non-flow effect.
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11. Invariant Mass Method Assume KS0
STAR preliminary
STAR preliminary
KS0
Assume
Borghini et al. Phys. Rev. C70 (2006)4905
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12. Pion and Proton Identification
TPC: pi/K ~ 0.7 GeV/c pi+K/p ~1.1 GeV/c
pi/p ~ > 3GeV/c relativistic rise
Cuts used for identification:
No. of fit hits > 15
No. of fit hits/No. of possible hits >0.52
pT < 1 (GeV/c) < nσπ (p) < 2
pT > 2.5 (GeV/c) 0 < nσπ < 1
-1 < nσp < 0
M. Shao, et al., Nuclear Instruments and Methods in Physics Research A 558 (2006)
pion purity: over 95%
proton purity: 70%
The effect on proton v2 will be about 10%.
Using Run 4 data result
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13. v2 {TPC} and v2 {FTPC} v2(pT) have been measured for , p, KS0 and .
Au+Au 200GeV (minibias)
STAR preliminary
STAR preliminary
v2(pT) have been measured for , p, KS0 and .
Non-flow effect reduced considerably by using the
FTPC event plane.
minibais result for centrality 0-80%
Na Li th Winter Workshop on Nuclear Dynamics

14. Number of Quark (Nq) Scaling
STAR preliminary
STAR preliminary
The number of quark scaling for , KS0 and  holds
up to (mT – m)/nq ~ 1 GeV/c2.
Protons seem to deviate from the scaling at lower pT.
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15. v4 {TPC} v4(pT) has been measured for , KS0 and .
STAR preliminary
STAR preliminary
v4(pT) has been measured for , KS0 and .
The Nq scaling for v4 is observed at (mT - m)/nq < 1 GeV/c2,
similar to that of v2.
Na Li th Winter Workshop on Nuclear Dynamics

16. Test of Ideal Hydro Predictions
STAR preliminary
v4 /v22 is about 1 at pT ~ 2 GeV/c, larger than the value
0.5 expected from ideal fluid calculations.
Na Li th Winter Workshop on Nuclear Dynamics

17. Summary FTPC event plane is used in STAR in order to reduce the
non-flow effect. Run 7 high statistics data used in this
analysis.
Proton and anti-proton seems to deviate from the
number of quark scaling at (mT - m)/nq ~ 1 GeV/c2 .
The number of quark scaling has been observed for v4 at
(mT - m)/nq < 1 GeV/c2.
Mesons and baryons (, KS0 and ) have similar v4/(v2)2
ratios. It is close to unity at pT > 1 GeV/c, higher than
ideal hydrodynamic model predictions.
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18. BACK UP
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19. Number of Quark (Nq) Scaling
STAR preliminary
STAR preliminary
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