Sadhana Dash

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Sadhana Dash Institute of Physics,
Bhubaneswar (For STAR Collaboration)
Outline
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Importance of K studies
K lifetime 4fm/c, ? sensitive to the
properties of hot and dense medium created.
Modification in K Mass , Width and pT spectra
? in-medium dynamical effects
K/?, ?/K ? information on interplay of
rescattering and regeneration effects .
v2 and RCP measurements of K provide
important information on its production mechanism
in the hot/dense phase of heavy ion collisions.
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Regeneration and Rescattering Effects
K reconstructed
Klost
K reconstructed
Chemical freeze-out
Thermal freeze-out
We study K/K ratio in pp and AA collisions
to understand rescattering effect.
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K Invariant Mass Spectrum
MinBias
MinBias
M0 and Gamma
Background Linear function
The signal was obtained by subtracting the
combinatorial background distribution (generated
using mixed event technique) from the kaon-pion
invariant mass distribution.
Phys. Rev. C 71 (2005) 064902
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STAR DATA (Run IV V) AuAu 62.4 GeV 7e6
events AuAu 200 GeV 13e6 events CuCu 62.4
GeV 10e6 events CuCu 200 GeV 8e6
events
STAR Time Projection Chamber was used to select
kaons and pions.
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K0 Mass and Width Distribution
K mass and width are consistent with PDG
values

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Centrality Dependence of Transverse Mass Spectra
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K0 dN/dy and ltpTgt
No significant centrality dependence of ltpTgt
for both AuAu and CuCu collisions at a given
energy.

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Particle Ratio (K/K-)
Rescattering crosssection, ????gt 5 times the
regeneration cross-section,????
Phys. Rev.D 9, 1872(1974)
There is a suppression of (K/K-)AA/(K/K-)pp
ratio with centrality gt rescattering effect
predominates over regeneration .
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Particle Ratio (F/K)
(?/K)AA/ (?/K)pp ratio increases with
centrality favouring rescattering effect more
K are destroyed than regenerated.
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Nuclear Modification Factor
RCP of K is smaller than ? and KS at lower pT
gt strong rescattering of daughter particles.
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Scaled particle momentum elliptic flow is same
for different species.
Phys. Rev Lett.92(2004)052302
Number of quarks from v2 scaling 4 gt
Kregeneration
Phys.Rev.C69 ,031902(2004)
Number of quarks is found to be 2.0 - 0.3 which
implies hadronic regeneration process contributes
little to the final observed K
AuAu at 200 GeV STAR Preliminary
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Summary
K(896) resonance production has been measured at
?sNN62.4 GeV and ?sNN200 GeV in both AuAu and
Cu Cu collisions by STAR at RHIC.
K0 integrated yield scales with dNch/d? in
both AuAu and CuCu collision systems. ltpTgt
shows no significant centrality or system size
dependence in AuAu and CuCu collisions.

Measurements of K0/K and ??/K0 ratio, v2, and
K RCP at low pT ???K ?are primarily formed
at hadronization.

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Summary (contd)
At intermediate pT , RCP measurements support
baryon -meson effect over mass effect of particle
production .
A non-zero K elliptic flow v2 was measured in
AuAu collisions at 200 GeV . At intermediate
pT , the number of quark constituents is found to
be 2.0-0.3 which suppports quark recombination
model of particle production.
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AuAu 62GeV
STAR PRELIMINARY
STAR PRELIMINARY
The signal was obtained by subtracting the
combinatorial background distribution (through
mixed event technique) from the kaon-pion
invariant mass distribution.
STAR TPC was used to select kaons and
pions. STAR DATA (Run IV V) AuAu 62.4 GeV
7e6 events AuAu 200 GeV 13e6
events CuCu 62.4 GeV 10e6 events CuCu 200
GeV 8e6 events
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