1. Parallel Session (Hadron 1) 2/Dec/97 Quark Matter ‘97 Kaon and Proton Ratios from Central Pb+Pb Collisions at the CERN SPS Masashi Kaneta for the NA44 collaboration Department of Physics, Hiroshima University ① Introduction ② m T distributions of K and p from Pb+Pb ③ Particle ratios ④ Summary e-mail: kaneta@hiroh2.hepl.hiroshima-u.ac.jp

2. Parallel Session (Hadron 1) 2/Dec/97 Quark Matter ‘97 Masashi Kaneta / Hiroshima univ. High energy heavy ion collision Thermal freeze-out Introduction E x p a n s i o n T fo ： ～ 140 MeV at SPS and AGS energies Lots of hadrons are newly created Huge number of collisions Thermo-chemical model To describe the system 

3. Parallel Session (Hadron 1) 2/Dec/97 Quark Matter ‘97 Masashi Kaneta / Hiroshima univ. 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,b, J.J.Gaardhøje 1, M.Hamelin 10, A.G.Hansen 1, O.Hansen 1, D.Hardtke 8, H. van Hecke 2, E.B.Holzer 6, T.Humanic 8, P.Hummel 9, B.V.Jacak 2,c, R.Jayanti 8, K.Kaimi 5, M.Kaneta 5, M.Kopytine 2,c, M.Leltchouk 3, A.Ljubicic Jr. 7, B.Lörstad 10, N.Maeda 5,d, R.Malina 6 M.Murray 10, H.Ohnishi 5, G.Paic 4,6, S.U.Pandey 8,e, F.Piuz 6, J.Pluta 4, V.Polychronakos 11, M.Potekhin 3, G.Poulard 6, D.Reichhold 8, A.Sakaguchi 5,f, J.Simon-Gillo 2, J.Schmidt-Sørensen 9, W.Sondheim 2, M.Spegel 8, T.Sugitate 5, J.P.Sullivan 2, Y.Sumi 5, W.J.Willis 3, K.L.Wolf 10, N.Xu 2,g and D. S. Zachary 8 Now at Universität Heidelberg, Physikalisches Institut, 69120 Heidelberg, Germany. Now at Brookhaven National Laboratory, Upton, NY 11973, USA. Now at State University of New York, Stony Brook, NY 11794, USA. Now at Department of Physics, Florida State University, Tallahassee, FL 32306-3016, USA. Now at Wayne State University, Detroit, MI 48202, USA. Now at Department of Physics, Osaka University, Toyonaka, Osaka 560, Japan. 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 Department of Physics, University of Lund, S-22362 Lund, Sweden. 10 Texas A&M University, College Station, TX 77843, USA. 11 Brookhaven National Laboratory, Upton, NY 11973, USA. The NA44 Collaboration abcdefgabcdefg

4. Parallel Session (Hadron 1) 2/Dec/97 Quark Matter ‘97 Masashi Kaneta / Hiroshima univ.

5. Parallel Session (Hadron 1) 2/Dec/97 Quark Matter ‘97 Masashi Kaneta / Hiroshima univ. PID

6. Parallel Session (Hadron 1) 2/Dec/97 Quark Matter ‘97 Masashi Kaneta / Hiroshima univ. Acceptance

7. Parallel Session (Hadron 1) 2/Dec/97 Quark Matter ‘97 Masashi Kaneta / Hiroshima univ. Selection of centrality

8. Parallel Session (Hadron 1) 2/Dec/97 Quark Matter ‘97 Masashi Kaneta / Hiroshima univ. K - /K + and p/p ratio as a function of P T and centrality

9. Parallel Session (Hadron 1) 2/Dec/97 Quark Matter ‘97 Masashi Kaneta / Hiroshima univ. m T distribution Inverse slope [MeV] dN/dy K+K-ppK+K-pp 237±3 21.3±0.8 238±3 11.5±0.4 303±6 25.3±1.0 281±8 1.64±0.09 systematic error: <4% for inverse slope <10% for dN/dy centrality : top 8.5%

10. Parallel Session (Hadron 1) 2/Dec/97 Quark Matter ‘97 Masashi Kaneta / Hiroshima univ. Effect for proton yield from weak decays Effects  of  and  + decay to proton spectra are estimated by a Monte-Carlo simulation (Also, antiparticle to antiproton) –dN/dy and m T slope are referred from RQMD(V1.08) and experimental data (NA49 coll., Nucl. Phys. A610 (1996) 188c) Inverse slope [MeV] dN/dy pppp 331±10±11 20.1±1.2±1.3 316±13±15 1.11±0.19±0.11 The error by correction reflected the result of increasing and decreasing the (  +  + )/p ratio by a factor of 1.5

11. Parallel Session (Hadron 1) 2/Dec/97 Quark Matter ‘97 Masashi Kaneta / Hiroshima univ. Strange neutral hadron gas model  s is given as a function of T ch and  q for different  s by numerical calculation. T ch,  q : 5MeV step  s : 0.05 step  s =1

12. Parallel Session (Hadron 1) 2/Dec/97 Quark Matter ‘97 Masashi Kaneta / Hiroshima univ. Extract chemical freeze-out temperature and chemical potentials T ch  q  s  s = 155 ～ 170 MeV = 75 ～ 85 MeV = 22 ～ 31 MeV = 0.75 ～ 0.95 comparison of ratios from experiment with ratios from model

13. Parallel Session (Hadron 1) 2/Dec/97 Quark Matter ‘97 Masashi Kaneta / Hiroshima univ. Comparison of T ch,  q,  s from Pb+Pb with those from other systems The T ch and  q in Pb+Pb are close to the values in S+A T ch ：  q ：  s : at SPS energies at AGS energies 155 ～ 200 MeV 120 ～ 140 MeV 60 ～ 120 MeV 160 ～ 200 MeV 3 ～ 40 MeV 60 ～ 120 MeV

14. Parallel Session (Hadron 1) 2/Dec/97 Quark Matter ‘97 Masashi Kaneta / Hiroshima univ. Summary Collisions system dependence of T ch,  q and  s is less clear than dependence At SPS energies, Chemical freeze-out temperature T ch > T fo ( ～ 140MeV) Chemical freeze-out temperature and chemical potentials are extracted from kaon and proton ratio in Pb+Pb collisions T ch  q  s  s = 155 ～ 170 MeV = 75 ～ 85 MeV = 22 ～ 31 MeV = 0.75 ～ 0.95 It is quite natural with view point of thermodynamics