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Particle Ratios from Central Pb+Pb Collisions at the CERN SPS. Masashi Kaneta for the NA44 collaboration Department of Physics, Hiroshima University. Introduction Particle Ratios Ratios as a function of centrality and P t Chemical property Thermal freeze-out Summary.

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## Particle Ratios from Central Pb+Pb Collisions at the CERN SPS

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**Particle Ratios from Central Pb+Pb Collisions at the CERN**SPS Masashi Kaneta for the NA44 collaboration Department of Physics, Hiroshima University • Introduction • Particle Ratios • Ratios as a function of centrality and Pt • Chemical property • Thermal freeze-out • Summary**The NA44 Collaboration**I. G. Bearden1, H. Bøggild1, J. Boissevain2, J. Dodd3, B. Erazmus4, S.Esumi5,A, C. W. Fabjan6, D. Ferenc7, D. E. Fields2, A, Franz6, J.J.Gaardhøje1, O, Hansen1, D. Hardtke8, H. van Hecke2, E. B. Holzer9, T. Humanic8, P. Hummel9, B. V. Jacak2, R. Jayanti8, M. Kaneta5, M. Kopytine2, M. Leltchouk3, T.Ljubicic7, B. Lörstad10, N. Maeda5,B, A. Medvedev3, M. Murray11, S. Nishimura5,C, H. Ohnishi5, G. Paic4,6, S. U. Pandey8, F. Piuz6, J. Pluta4, V. Polychronakos12, M. Potekhin3, G. Poulard6, A. Sakaguchi5,D, J. Simmon-Gillo2, J. Schmidt-Sørensen10, W. Sondheim2, M. Spegel9, T. Sugitate5, J. P. Sullivan2, Y. Sumi5, W.J.Willis3, K. Wolf11, N. Xu2,E and D. S. Zachary8 1 Niels Bohr Institute, DK-2100 Copenhagen, Denmark. 2 Los Alamos National Laboratory, Los Alamos, NM 87545 USA. 3 Department of Physics, Columbia University, New York, NY 10027, USA. 4 Nuclear Physics Laboratory of Nantes, 44072 Nantes, France. 5 Hiroshima University, Higashi-Hiroshima 739, Japan. 6 CERN, CH-1211 Geneva 23, Switzerland. 7 Rudjer Boskovic Institute, Zagreb, Croatia. 8 Department of Physics, Ohio State University, Columbus, OH 43210, USA. 9 Technical University, A-1040, Vienna, Austria. 10 Department of Physics, University of Lund, S-22362 Lund, Sweden. 11 Texas A&M University, College Station, TX 77843, USA. 12 Brookhaven National Laboratory, Upton, NY 11973, USA. A Now at Universität Heidelberg, Physikalisches Institut, 69120 Heidelberg, Germany. B Now at Department of Physics, Florida State University, Tallahassee, FL 32306-3016, USA. C Now at Institute of Physics, University of Tsukuba, Tsukuba, Ibaraki 305, Japan. D Now at Department of Physics, Osaka University, Toyonaka, Osaka 560, Japan. E Now at Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. Masashi Kaneta / Hiroshima univ.**Motivations**• Particle ratios • Sensitivity to collision dynamics • Check chemical equilibrium assumption • K-/K+, p/p ratios A Scenario Collisions Chemical equilibrium state？ Thermal equilibrium state Freeze-out Masashi Kaneta / Hiroshima univ.**PID**• Selection between K and p Masashi Kaneta / Hiroshima univ.**NA44 acceptance**Masashi Kaneta / Hiroshima univ.**Selection of centrality**Masashi Kaneta / Hiroshima univ.**Ratios as a function of Pt and centrality**• Those ratios are measured at the downstream (~20m) of collision point. • A effect of decayed particles is included in it. Masashi Kaneta / Hiroshima univ.**Effect of decayed particles**• Tools • RQMD : y, pT distribution • MC simulation : effect of acceptance As first step, lambda decay effect to proton yield is studied Example of Pt distribution pass p,p,L,L through NA44 detectors Correction factor for p/p ratio As systematic error { dN/dy: ±30% mt slope: ±10% Masashi Kaneta / Hiroshima univ.**Strangeness neutral hadron gas**Masashi Kaneta / Hiroshima univ.**Absolute ratio and ratio around mid rapidity**• NA44 acceptance for Kaons and protons are around mid rapidity. • compare ratios as a function of rapidity and absolute ratios in RQMD. NA44 preliminary RQMD ver 1.08 (b<2fm) ( average) Kaons : ratios around the mid rapidity is the same with absolute ratio. protons : both ratios are close in the region dy£1.6. Masashi Kaneta / Hiroshima univ.**Comparison with model prediction**Masashi Kaneta / Hiroshima univ.**Thermal freeze-out temperature**Masashi Kaneta / Hiroshima univ.**Summary**In Pb+Pb central collisions • Ratios • K-/K+and p/p ratios are flat as a function of Pt • Ratios are insensitive in the central region (top 8.5%) • Chemical properties • Assuming the system is in chemical equilibrium state • TemperatureTch ~ 175MeV • Chemical potentialmq ~ 80MeV, ms ~ 30MeV • Tch³ Tf0 Masashi Kaneta / Hiroshima univ.

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