K*(892) Resonance Production in Au+Au and Cu+Cu Collisions at  s NN = 200 GeV & 62.4 GeV

1. 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 Dash Institute of Physics, Bhubaneswar (For STAR Collaboration) Outline:

2. Features of K* Meson Charged-meson : Mass : 891.66 +/- 0.26 MeV Width : 50.80 +/- 0.90 MeV Decay Modes : K ~ 100 % Decay Modes for present study K0S K0 S BR ~ 23% ……….. Life time : ~ 4 fm Quark Structure : K*+ u s K*- u s Neutral K*-meson : Mass : 896.10 +/- 0.27 MeV Width : 50.70 +/- 0.60MeV Decay Modes : K ~ 100 % Decay Modes for present study K+  K-  BR ~ 66% ……….. Life time : ~ 4 fm Quark Structure : d s d s 2

3. 3 Importance of K* studies K* lifetime~4fm/c, sensitive to the properties of hot and dense medium created. Modification in K* Mass , Width and pTspectra in-medium dynamical effects K*/, /K*information on interplay of rescattering and regeneration effects . v2and RCPmeasurements of K* provide important information on its production mechanism in the hot/dense phase of heavy ion collisions.

4. K* thermally produced at the chemical freeze-out stage  K* Daughter particles’ Rescattering Effect destroys part of K* signal K K*   K Regeneration Effect compensates against lost K* yield K*   K* K K K time 4 Regeneration and Rescattering Effects K*reconstructed K*lost K*reconstructed Chemical freeze-out Thermal freeze-out We study K*/K ratio in p+p and A+A collisions to understand rescattering effect.

5. STAR Experiment 5 STAR DATA (Run IV & V) Au+Au 62.4 GeV ~ 7e+6 events Au+Au 200 GeV ~ 13e+6 events Cu+Cu 62.4 GeV ~ 10e+6 events Cu+Cu 200 GeV ~ 8e+6 events STAR Time Projection Chamber was used to select kaons and pions.

6. Signal : Simple Breit-Wigner 00202/4] 6 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

7. 7 K*0 Mass and Width Distribution K* mass and width are consistent with PDG values

8. Exponential Fitfunction: d2N dN/dy 1 exp {-(mT-m0)/T} 2πmT dmTdy 2 πmT(m0+T) 8 Centrality Dependence of Transverse Mass Spectra

9. The integrated yields of K* scale with charged particle multiplicity for Au+Au and Cu+Cu collisions at 62.4 GeV and 200 GeV. K* 200GeV (Run II) : Phys. Rev. C 71 (2005) 064902 9 K*0 dN/dy and <pT> No significant centrality dependence of <pT> for both Au+Au and Cu+Cu collisions at a given energy.

10. 10 Particle Ratio (K*/K-) Rescattering crosssection, > 5 times the regeneration cross-section, Phys. Rev.D 9, 1872(1974) There is a suppression of (K*/K-)A+A/(K*/K-)p+p ratio with centrality => rescattering effect predominates over regeneration .

11. Particle Ratio (Φ/K*) (/K*)A+A/ (/K*)p+p ratio increases with centrality favouring rescattering effect: more K* are destroyed than regenerated. 11

12. Run IV Baryon-mesoneffect is favored in particle production 12 Nuclear Modification Factor RCPof K* is smaller thanandKSat lower pT => strong rescattering of daughter particles.

13. K* v2 13 Scaled particle momentum elliptic flow is same for different species. Phys. Rev Lett.92(2004)052302 Number of quarks from v2 scaling = 4 => K*regeneration 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* Au+Au at 200 GeV STAR Preliminary

14. 14 Summary 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. K*0integrated 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. Measurements of K*0/K and/K*0 ratio, v2, and K* RCPat low pTK* are primarily formed at hadronization.

16. 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 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. 15

18. Typical Invariant Mass Spectrum Fit function : Signal : Simple Breit-Wigner 00202/4] 0 : K* width 0 : K* mass Background : Linear function 18 QM-08 Sadhana Dash Jaipur, Feb 04 - 10 Au+Au 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) Au+Au 62.4 GeV ~ 7e+6 events Au+Au 200 GeV ~ 13e+6 events Cu+Cu 62.4 GeV ~ 10e+6 events Cu+Cu 200 GeV ~ 8e+6 events

19. K* <pT> in comparison with other species 19