Event by Event fluctuations in k/pi ratio in the STAR Experiment at RHIC

1. Event by Event fluctuations in k/pi ratio in the STAR Experiment at RHIC Neeraj Gupta1 and Zubayer Ahammed2 for the STAR Collaboration • Dept. of Physics and Electronics, University of Jammu, Jammu. • Variable Energy Cyclotron Centre, 1/AF, BidhanNagar, Kol-64. Outline: • Introduction • Earlier Measurements • Particle Identification in STAR • Analysis Methods • Results and Discussions • Summary

2. Introduction • QCD predicts QGP phase transition at sufficient high temperature/ energy density. • The nature of this phase transition can be reflected in the increased/reduced fluctuations in the global observables. • Kapusta and Mekjian[Ref.] suggested that such fluctuations in the Kaon to Pion ratio can reflect the nature of such phase transition. Ref. J.I. Kapusta and A. Mekjien, Phys. Rev. D33(1986)1304

3. Earlier Measurements (NA49 Collaboration) S. Afanasiev for NA49 PRL 86 (2001) C. Roland QM 2004 Increased fluctuation signal at lower beam energies for k /pi

4. Earlier Measurements(STAR Collaboration) (QM06) Au+Au Au+Au Au+Au Au+Au Similar fluctuations strength for Au+Au at 62 and 200 AGeV

5. STAR Detectors Tracking Detectors: TPC, FTPC, SVT Calorimeters: BEMC, EEMC, ZDC Trigger Detectors: CTB, BBC, MWPC Photon Detector: PMD Others:TOF, FPD

6. Particle Identification in STAR M. Anderson et al. for STAR Collaboration, NIMA499 (2003) Data Quality Cuts in the present analysis • The momentum of the track(pt)~ 0.15<pt<0.6 • Primary vertext of the event, z-vertex<25cm • Distance of closest approach of the track, dca<3cm • The number of hits in TPC pads, Nhit>15 • Ratio of nhit and number of fit points, Nhit/nFits>0.5 Kaons: nskaon < 2 && nspion > 2 Pions: nspion < 2 && nskaon > 2

7. Measures Dynamical Fluctuations = Total Fluctuations - Statistical Fluctuations Due to finite number statistics Reflects dynamics and response of the system Estimation of sdynamical: s = RMS/MEAN sdyn = (s2data – s2mixed) Where, s_data is the widtdth of k/pi distribution from real data and s_mixed is the is that of mixed events.

8. Measures n_dynamical: This variable is based on two particle correlations. Proposed by Pruneau, Gavin and Voloshin PRC 66(2002). This variable is supposed to be independent of detector inefficiency. Independent of detector inefficiency

9. Mixed Events: Mixed events is constructed to get the statistical fluctuation due to finite number statistics and experimental resolution. • Mixed Events are constructed taking one track from each event randomly. • Keep the multiplicity of the mixed event same as that of the real event . • All the parameters of the track is kept in the mixed event array. • Apply same cuts as the real events • Calculate number of Kaons and Pions event by event and their ratio.

10. Mixed Events QA <Pions> Data: 165.6 Mixed :165.6 STAR Preliminary STAR Preliminary <Kaons> Data:10.39 Mixed:10.4 STAR Preliminary

11. Results 62 AGeV: sdynamical = 6.10.67 Cu+Cu 62AGeV STAR Preliminary 200 AGeV: sdynamical = 5.30.53 Cu+Cu 200AGeV Similar within errors for both the energy. STAR Preliminary

12. Comparison with SPS and STAR Au+Au STAR Cu+Cu Cu+Cu: Similar at 62 and 200 AGeV(within errors) Slightly larger than Au+Au

13. Results STAR Preliminary STAR Preliminary Cu+Cu 200AGeV Cu+Cu 200AGeV The scaled nu_dynamical fluctuations with total charged particles almost constant with centrality.

14. Summary • Dynamical fluctuations in K/pi ratio is measured for Cu+Cu system. • The sdynamical is similar for 62 AGeV and 200 AGeV Cu+Cu system • The scaled nu_dynamical fluctuations with total charged particles almost constant with centrality.