1. INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997 Particle Ratios from Central Pb+Pb Collisions at the CERN SPS Masashi Kaneta for the NA44 collaboration Department of Physics, Hiroshima University ① Introduction ② Particle Ratios Ratios as a function of centrality and P t Chemical property Thermal freeze-out ③ Summary

2. INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997 Masashi Kaneta / Hiroshima univ. 2 I. G. Bearden 1, H. Bøggild 1, J. Boissevain 2, J. Dodd 3, B. Erazmus 4, S.Esumi 5,A, C. W. Fabjan 6, D. Ferenc 7, D. E. Fields 2, A, Franz 6, J.J.Gaardhøje 1, O, Hansen 1, D. Hardtke 8, H. van Hecke 2, E. B. Holzer 9, T. Humanic 8, P. Hummel 9, B. V. Jacak 2, R. Jayanti 8, M. Kaneta 5, M. Kopytine 2, M. Leltchouk 3, T.Ljubicic 7, B. Lörstad 10, N. Maeda 5,B, A. Medvedev 3, M. Murray 11, S. Nishimura 5,C, H. Ohnishi 5, G. Paic 4,6, S. U. Pandey 8, F. Piuz 6, J. Pluta 4, V. Polychronakos 12, M. Potekhin 3, G. Poulard 6, A. Sakaguchi 5,D, J. Simmon-Gillo 2, J. Schmidt-Sørensen 10, W. Sondheim 2, M. Spegel 9, T. Sugitate 5, J. P. Sullivan 2, Y. Sumi 5, W.J.Willis 3, K. Wolf 11, N. Xu 2,E and D. S. Zachary 8 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. 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. The NA44 Collaboration

3. INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997 Masashi Kaneta / Hiroshima univ. 3 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 Motivations

4. INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997 Masashi Kaneta / Hiroshima univ. 4

5. INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997 Masashi Kaneta / Hiroshima univ. 5 PID Selection between K and p

6. INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997 Masashi Kaneta / Hiroshima univ. 6 NA44 acceptance

7. INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997 Masashi Kaneta / Hiroshima univ. 7 Selection of centrality

8. INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997 Masashi Kaneta / Hiroshima univ. 8 Ratios as a function of P t and centrality †Those ratios are measured at the downstream (~20m) of collision point.  A effect of decayed particles is included in it.

9. INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997 Masashi Kaneta / Hiroshima univ. 9 Effect of decayed particles Tools –RQMD : y, p T distribution –MC simulation : effect of acceptance As first step, lambda decay effect to proton yield is studied pass p, p, ,  through NA44 detectors Example of P t distribution dN/dy: ±30% m t slope: ±10% As systematic error { Correction factor for p/p ratio

10. INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997 Masashi Kaneta / Hiroshima univ. 10 Strangeness neutral hadron gas

11. INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997 Masashi Kaneta / Hiroshima univ. 11 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) : ratios around the mid rapidity is the same with absolute ratio. Kaons protons : both ratios are close in the region  y  1.6.

12. INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997 Masashi Kaneta / Hiroshima univ. 12 Comparison with model prediction

13. INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997 Masashi Kaneta / Hiroshima univ. 13 Thermal freeze-out temperature

14. INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997 Masashi Kaneta / Hiroshima univ. 14 Summary Ratios –K - /K + and p/p ratios are flat as a function of P t –Ratios are insensitive in the central region (top 8.5%) Chemical properties –Assuming the system is in chemical equilibrium state  Temperature T ch ~ 175MeV  Chemical potential  q ~ 80MeV,  s ~ 30MeV  T ch  T f0 In Pb+Pb central collisions