K* Resonance Production in Au+Au and Cu+Cu collisions at RHIC

1. K* Resonance Production in Au+Au and Cu+Cu collisions at RHIC Sadhana Dash (for the STAR Collaboration) Institute of Physics ,Bhubaneswar ,India PLAN MOTIVATION ANALYSIS AND RESULTS SUMMARY 1

2. Features of K* Meson Some features of Neutral -meson : Mass : 896.10 +/- 0.27 MeV Width : 50.70 +/- 0.60 MeV Decay Modes : K ~ 100 % Decay Modes for present study K+  K-  BR ~ 66% ……….. Life time : ~ 4 fm Quark Structure : Particle d sbar anti-particle dbar s 2

3. K* lifetime ~4fm/c, comparable to lifetime of the hot dense matter (few fm/c)  sensitive to the properties of hot dense matter K* Mass and width modification in-medium dynamical effects Compared to other particles (K*/K)  information on K* production mechanism and (timing) on chemical freeze-out andthermal freeze-out conditions 3 Motivation : Why measure K*? /K* information on rescattering effect and/or strangeness enhancement

4. K* thermally produced at the chemical freeze-out stage  K*  K K* Daughter particles’ Rescattering Effect destroys part of K* signal K*lost  K K*   K* Regeneration Effect compensates K* yield K K K K* measured K*/K reveals timing between chemical and thermal freeze-out time 4 K* : Regeneration and Rescattering Effect K* measured Chemical freeze-out Thermal freeze-out

5. Typical Invariant Mass Spectrum Fit function : Signalnon-relativistic Breit-Wigner function 00202/4] Background linear function 0 : K* width 0 : K* mass 5 Au+Au 62GeV STAR PRELIMINARY The signal was obtained by subtracting the combinatorial background distribution (through mixed event technique) from the kaon-pion invariant mass distribution.

6. K* mass approaches PDG value at high-pT K* mass shifted ~10 MeV at low-pT K* width agrees with PDG value K* 200GeV from Phys. Rev. C 71 (2005) 064902 6 K*0 Mass and Width Distributions STAR PRELIMINARY MC PDG STAR PRELIMINARY PDG

7. Cu+Cu 62.4 Cu+Cu 200 7 K*0 Transverse Momentum Spectra STAR PRELIMINARY STAR PRELIMINARY STAR PRELIMINARY Au+Au 62.4 K*0 spectra fit to an exponential function pT -exponential fit to the measured data is used for extrapolation outside the fiducial range

8. K* 200GeV from Phys. Rev. C 71 (2005) 064902 K* dN/dy increases with Npart and dNch/d in both Cu+Cu and Au+Au collision. 8 K*0 dN/dy vs. Centrality & dNch/d STAR PRELIMINARY STAR PRELIMINARY

9. 9 Particle Ratios and <pT> STAR PRELIMINARY STAR PRELIMINARY • K*0/K in Au+Au 62.4 GeV is comparable to the Au+Au 200 value • Φ/K*0is lower in Au+Au 62.4  rescattering plays a major role as we go high in energy • No significant centrality dependence of <pT> for both Au+Au and Cu+Cu systems • <pT> for Au+Au and Cu+Cu at 200 GeV is higher than that of both systems in 62.4 GeV indicating energy dependence STAR PRELIMINARY Statistical errors only STAR PRELIMINARY

10. 10 Summary K*(896) resonance production has been measured at sNN=62.4 GeV andsNN=200 GeVin both Au+Au and Cu+ Cu collisions at STAR K*0 mass and width approaches the PDG value at higher pT inboth Au+Au and Cu+Cu collisions. K*0 dN /dy in Au+Au and Cu+Cuincreases with number of participants, <pT> shows no significant centrality or system sizedependencein Au+Au and Cu+Cu collisions. K*0/K ratiodaughter particles’ rescattering /K*0rescattering effect dominant in Au+Aucolisionsat 200GeV