System Size Dependence of fmeson Production at RHIC

1
System Size Dependence of fmeson Production at
RHIC

• Xinghua Shi(SINAP/LBNL)
• For STAR Collabration

2
Overview

• Introduction
• System size dependence of f-meson production at
  RHIC
• Strange hadron elliptic flow from 200GeV CuCu
  collisions

1
3
What we want to know

• Physics of hot dense matter
• Evolution of the universe

2
4
Empirical Evidence of (S)QGP at RHIC
Partonic energy loss
Away-side yield difference
Number of quark scaling v2 decrease
3
5
Relativistic Heavy Ion Collider (RHIC) at
Brookhaven
1 km
4
animation by Mike Lisa
6
Motivation of studying f

• Some features of f-meson
• Mass 1019.456 /- 0.020 MeV
• Width 4.26 /- 0.05 MeV
• Decay Mode KK- 49.2
• C 45fm (longer than fireball lifetime)
  
  
  
  
• Quark Structure s s (referred to as hidden
  strangeness)
• There might be small hadronic interaction
  cross sections
• Asher Shor al. Phy.Rev.Lett541122-1125,1985

f production can be a good probe
Information from earlier time Sensitive to
partonic flow
We have measured the productions of ?-meson for
various colliding energies and systems at RHIC
5
7
Transverse Momentum Spectra
STAR Preliminary
6
8
dN/dy and ltpTgt
STAR Preliminary
7
9
Strangeness Enhancement
STAR Preliminary
8
10
Anisotropy Parameter v2
Coordinate-Space Anisotropy
Momentum-Space Anisotropy
9
11
Reaction Plane Determination in STAR
TPC or FTPC reaction-plane
Why we use FTPC reaction-plane? The non-flow
correlation and auto correlation effects are
smaller from FTPC reaction-plane

10
12
Non-flow effects

• At intermediate and high pT
• v2FTPC lt v2TPC
• This indicates non-flow effect is reduced by
  using FTPC reaction plane.

STAR Preliminary
11
13
Strange Hadron v2 in CuCu 200GeV
At low pT, v2 of heavier ? is smaller than that
of KS0. KS0 and ? v2 cross over at pT 1.5 to 2
GeV/c. ? reaches higher v2 value at higher pT
than KS0. At high pT, the value of v2
decreases. F and ? have sizable v2.
STAR Preliminary
12
14
System Size Dependence
STAR Preliminary
STAR Preliminary

• Similar pT behavior for CuCu and AuAu
  collisions.
• v2 in low pT has the same value AuAu v2 seems
  greater than CuCu v2 in intermediate and high
  pT.
• Number-of-Quark scaling both observed in CuCu
  and AuAu collisions.
• The larger the system the stronger the
  collectivity.
• Compared to AuAu collisions, the v2/(nqltv2gtch)
  saturates at lower (mT-m)/nq.
• The same value of v2/(nqltv2gtch) in the low and
  intermediate (mT-m)/nq can be observed in CuCu
  and AuAu collisions

STAR Preliminary
13
15
Local thermalization at RHIC
Yan Lu et al. Phys.Rev.C 77,054901(2008)
STAR Preliminary

• The hydrodynamic calculations (assuming local
  thermalization ) show that v2 approximately
  scales with the eccentricity. Compared to the
  experimental data, it indicates the system
  created in AuAu 200GeV collisions may reach
  local thermalization only in the most central
  collisions.
• Comparing to v2 from AuAu 200GeV collision, we
  can reasonably come
• to the conclusion

The system created in CuCu 200GeV collisions
might not reach
local thermalization.
14
16
Summary

• We reported the observation of the ?-meson
  production in CuCu collisions.
• The transverse momentum spectra in both shape and
  yields are similar in CuCu and AuAu for
  collisions with similar Npart
• The ?-meson enhancement cannot solely due to
  canonical suppression of strangeness production,
  there could be dynamics effect.
• Preliminary 200GeV CuCu Ks0, ? and ? v2
• The larger system the stronger elliptic flow
• The system created in CuCu 200GeV collisions
  might not reach local thermalization

Thanks!
15
17
Reaction Plane from FTPC