1. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Chemical Property in Heavy Ion Collisions Masashi Kaneta for the NA44 collaboration Department of Physics, Hiroshima University ① Introduction ② Particle Ratios from NA44 Ratios as a function of centrality and P T Chemical property ③ Chemical freeze-out ④ Thermal freeze-out ⑤ Summary

2. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Masashi Kaneta / Hiroshima univ. 2 Particle ratios –Sensitivity to collision dynamics –Check chemical equilibrium assumption A Scenario Motivations Collisions Thermal freeze-out Chemical freeze-out ？ E x p a n s i o n

3. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Masashi Kaneta / Hiroshima univ. 3 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, A.G. Hansen 1,O. Hansen 1, D. Hardtke 8, H. van Hecke 2, E.B. Holzer 9, T.J. Humanic 8, P. Hummel 9, B.V. Jacak 2, R. Jayanti 8, M. Kaneta 5, M. Kopytine 2, M. Leltchouk 3, A. 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, D. Reichhold 8, 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 Department of Physics, 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

4. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Masashi Kaneta / Hiroshima univ. 4 CERN experiment NA44 Study the space-time evolution and temperature of nuclear collisions Measure one- and two-particle distributions of charged hadron  around mid-rapidity ( y lab  3 )  0  P T  1.6 GeV/c  TOF resolution  100ps   P/P  0.5% (@ nominal P = 8GeV) Recent publications –Phys. Rev. Lett. 78 (1996) 2080 Collective expansion in high energy heavy ion collisions –Phys. Lett. B388 (1996) 431 Mid-rapidity protons in 158 A GeV Pb+Pb collisions –Phys. Lett. B372 (1996) 339 Coulomb effect in Single Particle Distributions

5. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Masashi Kaneta / Hiroshima univ. 5

6. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Masashi Kaneta / Hiroshima univ. 6 PID Selection between K and p

7. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Masashi Kaneta / Hiroshima univ. 7 NA44 acceptance

8. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Masashi Kaneta / Hiroshima univ. 8 Selection of centrality

9. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Masashi Kaneta / Hiroshima univ. 9 Ratios as a function of P T and centrality †Those ratios are measured downstream (~20m) from collision point.  The feed-down from resonance is included in it.  correction factor for p/p: 0.9 ± 0.1

10. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Masashi Kaneta / Hiroshima univ. 10 Strangeness neutral hadron gas

11. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Masashi Kaneta / Hiroshima univ. 11 Comparison ratios with model prediction

12. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Masashi Kaneta / Hiroshima univ. 12 Chemical freeze-out There is model dependence for chemical freeze-out temperature and chemical potential. In general, –the system in SPS energy is higher chemical freeze-out temperature and lower baryon density than one in AGS energy

13. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Masashi Kaneta / Hiroshima univ. 13 Thermal freeze-out (a) Positive (b) Negative The dashed lines in figure are fits to the function : Boltzmann distribution The slope parameter T depends on particle mass Transverse mass distributions Phys. Rev. Lett. 78 (1996) 2080

14. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Masashi Kaneta / Hiroshima univ. 14 Thermal freeze-out temperature Slope parameter T and particle mass m may be described by the relation ship T = T fo + m 2 T fo : freeze-out temperature : averaged collective flow velocity At SPS At AGS T fo = 140±10 MeV T fo = 145±15 MeV Phys. Rev. Lett. 78 (1996) 2080

15. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Masashi Kaneta / Hiroshima univ. 15 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 from SPS Chemical freeze-out and Thermal freeze-out temperatures SPS: AGS: T ch [MeV] T fo [MeV] 170 ～ 210 130 ～ 150 140±10 145±15

16. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Masashi Kaneta / Hiroshima univ. 16 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

17. International School on the Physics of Quark Gluon Plasma June 3-6, 1997, Hiroshima Masashi Kaneta / Hiroshima univ. 17 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.