K*(892) Resonance Production in Au+Au and Cu+Cu Collisions at  s NN = 200 GeV & 62.4 GeV Motivation Analysis and Results Summary 1 Sadhana Dash Institute of Physics, Bhubaneswar (For STAR Collaboration) Outline:

Neutral K*  - meson : Mass : / MeV Width : /- 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 Features of K* Meson 2 Charged   - meson : Mass : / MeV Width : / MeV Decay Modes : K  ~ 100 % Decay Modes for present study K 0 S   K 0 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 p T spectra  in-medium dynamical effects v 2 and R CP 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 * los t  K K*K*   K*K* K K K * reconstructed Regeneration Effect compensates against lost K* yield Chemical freeze-out Thermal freeze-out K*K* time K*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 combinatorial background distribution (generated using mixed event technique) from the kaon-pion invariant mass distribution. K* Invariant Mass Spectrum  0  0  2  0 2 /4] Signal : Simple Breit-Wigner 5 Background : Linear function M0 and Gamma Phys. Rev. C 71 (2005) MinBias

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 events Au+Au 200 GeV ~ 13e+6 events Cu+Cu 62.4 GeV ~ 10e+6 events Cu+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 d 2 N dN/dy 2πm T dm T dy 2 πm T (m 0 +T) 1 exp {-(m T -m 0 )/T}

K *0 dN/dy and The integrated yields of K* scale with charged particle multiplicity for Au+Au and Cu+Cu collisions at 62.4 GeV and 200 GeV. 9 K* 200GeV (Run II) : Phys. Rev. C 71 (2005) No significant centrality dependence of 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 R CP 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 which implies hadronic regeneration process contributes little to the final observed K* Phys. Rev Lett.92(2004) Number of quarks from v 2 scaling = 4 => K*regeneration Phys.Rev.C69,031902(2004) Au+Au at 200 GeV STAR Preliminary

K*(896) resonance production has been measured at  s NN =62.4 GeV and  s NN =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 p T  are primarily formed at hadronization. K* 0 integrated yield scales with dN ch /d  in both Au+Au and Cu+Cu collision systems. shows no significant centrality or system size dependence in Au+Au and Cu+Cu collisions. Summary 14

At intermediate p T, R CP 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 p T, the number of quark constituents is found to be which suppports quark recombination model of particle production. Summary (contd) 15

Typical Invariant Mass Spectrum The signal was obtained by subtracting the combinatorial background distribution (through mixed event technique) from the kaon-pion invariant mass distribution.  0  0  2  0 2 /4] Fit function :  0 : K* width  0 : K* mass STAR PRELIMINARY Au+Au 62GeV Signal : Simple Breit-Wigner Background : Linear function STAR PRELIMINARY 18 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 QM-08 Sadhana Dash Jaipur, Feb

K* in comparison with other species 19