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K*(892) Resonance Production in Au+Au and Cu+Cu Collisions at sNN = 200 GeV & 62.4 GeV
Motivation
Analysis and Results
Summary
1
Sadhana DashInstitute of Physics, Bhubaneswar
(For STAR Collaboration)
Outline:
Neutral K* -meson :
Mass : 896.10 +/- 0.27 MeV Width : 50.70 +/- 0.60MeVDecay Modes : K ~ 100 %Decay Modes for present study K+
K-
BR ~ 66% ……….. Life time : ~ 4 fm Quark Structure : d s d s
Features of K* Meson
2
Charged -meson :
Mass : 891.66 +/- 0.26 MeV Width : 50.80 +/- 0.90 MeVDecay Modes : K ~ 100 %Decay Modes for present study K0
S
K0 S
BR ~ 23% ……….. Life time : ~ 4 fm Quark Structure : K*+ u s K*- u s
Importance of K* studies
3
K*/, /K* information on interplay of rescattering and regeneration effects .
Modification in K* Mass , Width and pT
spectra in-medium dynamical effects
v2 and RCP
measurements of K* provide important information on its production mechanism in the hot/dense phase of heavy ion collisions.
K* lifetime ~4fm/c, sensitive to the properties of hot and dense medium created.
K* thermally produced at the chemical freeze-out stage
K*lost
K
K*
K*
K K K*
reconstructed
Regeneration Effect compensatesagainst lost K* yield
Chemical freeze-out
Thermal freeze-out
K*
time
K*
K
Daughter particles’ Rescattering Effect destroys part of K* signal
K
Regeneration and Rescattering Effects
4
We study K*/K ratio in p+p and A+A collisions to understand rescattering effect.
K*
reconstructed
The signal was obtained by subtracting the combinatorialbackground distribution (generated using mixed event technique) from the kaon-pion invariant mass distribution.
K* Invariant Mass Spectrum
0
02
02/4] Signal : Simple Breit-Wigner
5
Background : Linear functionM0 and Gamma
Phys. Rev. C 71 (2005) 064902
MinBiasMinBias
6
STAR Time Projection Chamber was used to select kaons and pions.
STAR Experiment
STAR DATA (Run IV & V)Au+Au 62.4 GeV ~ 7e+6 eventsAu+Au 200 GeV ~ 13e+6 eventsCu+Cu 62.4 GeV ~ 10e+6 eventsCu+Cu 200 GeV ~ 8e+6 events
K*0 Mass and Width Distribution
7
K* mass and width are consistent with PDG values
Centrality Dependence of Transverse Mass Spectra
Exponential Fit function:
8
d2N dN/dy 2πmT dmTdy 2 πmT(m0+T)
1exp {-(mT-m0)/T}
K*0 dN/dy and <pT>
The integrated yields of K* scale with charged particle multiplicityfor Au+Au and Cu+Cu collisions at 62.4 GeV and 200 GeV.
9
K* 200GeV (Run II) : Phys. Rev. C 71 (2005) 064902
No significant centrality dependence of <pT> for both Au+Au and Cu+Cu collisions at a given energy.
There is a suppression of (K*/K-)A+A
/(K*/K-)p+p
ratio with centrality => rescattering effect predominates over regeneration . 10
Rescattering crosssection> 5 times the regeneration cross-section,
Phys. Rev.D 9, 1872(1974)
Particle Ratio (K*/K-)
(/K*)
A+A/ (/K*)
p+p ratio increases with centrality favouring
rescattering effect: more K* are destroyed than regenerated.
Particle Ratio (Φ/K*)
11
Nuclear Modification Factor
Baryon-meson effect is favored in particle production
12
Run IV
RCP
of K* is smaller than and K
S at lower p
T => strong
rescattering of daughter particles.
K* v2
13
Scaled particle momentum elliptic flow is same for different species.
Number of quarks is found to be 2.0 +- 0.3 which implies hadronic regeneration process contributes little to the final observed K*
Phys. Rev Lett.92(2004)052302
Number of quarks from v2 scaling = 4 => K*regenerationPhys.Rev.C69 ,031902(2004)
Au+Au at 200 GeV
STAR Preliminary
K*(896) resonance production has been measured at sNN=62.4 GeV and sNN=200 GeV in both Au+Au and Cu+ Cu collisions by STAR at RHIC.
Measurements of K*0/K and /K*0 ratio, v2, and K* R
CP at low pT are primarily
formed at hadronization.
K*0 integrated yield scales with dNch
/d in both Au+Au and Cu+Cu collision systems.
<pT> shows no significant centrality or system size dependence in Au+Au and Cu+Cu collisions.
Summary
14
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 Au+Au 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.
Summary (contd)
15
Typical Invariant Mass Spectrum
The signal was obtained by subtracting the combinatorialbackground distribution (through mixed event technique) from the kaon-pion invariant mass distribution.
0
02
02/4]
Fit function :
0
: K* width
0 : K*
massSTAR PRELIMINARY
Au+Au 62GeV
Signal : Simple Breit-Wigner
Background : Linear functionSTAR PRELIMINARY
18
STAR TPC was used to selectkaons and pions.
STAR DATA (Run IV & V)Au+Au 62.4 GeV ~ 7e+6 eventsAu+Au 200 GeV ~ 13e+6 eventsCu+Cu 62.4 GeV ~ 10e+6 eventsCu+Cu 200 GeV ~ 8e+6 eventsQM-08 Sadhana Dash Jaipur, Feb 04 - 10
K* <pT> in comparison with other species
19