System Size and Energy Dependence

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System Size and Energy Dependence of ?-meson
Production at RHIC X.Z. Caia) for the STAR
Collaboration a) Nuclear Physics division,
Shanghai Institute of Applied Physics,
2
?-meson production from AuAu
ltpTgt
f/K-
STAR Col. Phys. Lett. B 612, 181 (2005),
Phys. Rev. Lett. 99, 112301 (2007).
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W and f mostly from bulk s quarks
And bulk s quarks have collective elliptic flow !
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The STAR experiment

• Event-mixing method used to estimate
  combinatorial background from uncorrelated KK-
  pairs
• Final subtracted minv distribution fitted with
  Breit-Wigner straight line.

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? mass
0-10 10-19 19-28 28-36
STAR Preliminary
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spectra
STAR Preliminary
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dN/dy and ltpTgt

• The dN/dy and ltpTgt are similar for CuCu and
  AuAu at similar Npart bin for the same
  collisions energy.
• f yields from AuAu and CuCu collisions depend
  on the number of participant nucleons only,
  unlike Kaon and hyperons.
• see STAR Xiaobin Wang parallel session VII

1 NA49 Col. Phys. Rev. Lett. 96, 052301
(2005) 2 E-802 Col. Phys. Rev. C 60, 044904
(1999).
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Nuclear Modification factor
STAR Preliminary
Comparing central AuAu and central CuCu with
peripheral AuAu Collisions 1) the yield and
pT shape depend on number of participants only
2) in terms of number of binary collisons the
CuCu data is higher indicating given the
same top 10 centrality CuCu has less number of
collisions per participant
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Strangeness enhancement
X
K, L
200 GeV
62.4 GeV
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Summary

• We present a study of the system size and energy
  dependence of ?-meson production at RHIC.
• The transverse momentum spectra in both shape and
  yields are similar in CuCu and AuAu for
  collisions with similar Npart
• ?-meson enhancement shows a distinct collision
  centrality and energy dependence. The enhancement
  factor of the ?-meson production (yield per
  Npart) lies between those of K/L and X, and
  decreases from 200 GeV to 62.4 GeV data unlike
  hyperons.
• The ?-meson enhancement cannot solely due to
  canonical suppression of strangeness production,
  there could be dynamics effect.

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N(?)/N(p)