kaon and proton ratios from central pb+pb collisions at the cern sps

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 mT distributions of K and p from Pb+Pb

③ Particle ratios

④ Summary

e-mail: [email protected]

Masashi Kaneta / Hiroshima univ.


High energy heavy　 ion collision

Thermal freeze-out

Introduction

E x

p a

n s

i o

n

Tfo ：～ 140MeV at SPS and AGS energies

Lots of hadrons are newly createdHuge number of collisions

Thermo-chemical model To describe the system



I.G.Bearden1, H.Bøggild1, J.Boissevain2, J.Dodd3,

B.Erazmus4, S.Esumi5,a, C.W.Fabjan6, D.Ferenc7,

D.E.Fields2, A.Franz6,b, J.J.Gaardhøje1, M.Hamelin10,

A.G.Hansen1, O.Hansen1, D.Hardtke8, H. van Hecke2,

E.B.Holzer6, T.Humanic8, P.Hummel9, B.V.Jacak2,c, R.Jayanti8,

K.Kaimi5, M.Kaneta5, M.Kopytine2,c, M.Leltchouk3,

A.Ljubicic Jr.7, B.Lörstad10, N.Maeda5,d, R.Malina6

M.Murray10, H.Ohnishi5, G.Paic4,6,

S.U.Pandey8,e, F.Piuz6, J.Pluta4, V.Polychronakos11,

M.Potekhin3, G.Poulard6, D.Reichhold8, A.Sakaguchi5,f,

J.Simon-Gillo2, J.Schmidt-Sørensen9, W.Sondheim2,

M.Spegel8, T.Sugitate5, J.P.Sullivan2, Y.Sumi5,

W.J.Willis3, K.L.Wolf10, N.Xu2,g and D. S. Zachary8

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

a

b

c

d

e

f

g



PID



Acceptance



Selection of centrality



K-/K+ and p/p ratio as a function of PT

and centrality



mT distribution

Inverse slope [MeV] dN/dy

K+

K-

pp

237±3 21.3±0.8 238±3 11.5±0.4303±6 25.3±1.0281±8 1.64±0.09

systematic error: <4% for inverse slope <10% for dN/dy

centrality : top 8.5%



Effect for proton yield from weak decays

• Effectsof and + decay to proton spectra are estimated by a Monte-Carlo simulation (Also, antiparticle to antiproton)

– dN/dy and mT slope are referred from RQMD(V1.08) and experimental data

(NA49 coll., Nucl. Phys. A610 (1996) 188c)

Inverse slope [MeV] dN/dy

pp

331±10±11 20.1±1.2±1.3316±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



Strange neutral hadron gas model

s is given as a function of Tch and q for differents by numerical calculation. Tch, q : 5MeV step s : 0.05 step

s=1



Extract chemical freeze-out temperature and chemical potentials

Tch

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



Comparison of Tch, q, s from Pb+Pb with those from other systems

The Tch and q in Pb+Pb are close to the values in S+A

Tch ：q ：s :

at SPS energies at AGS energies

155 ～ 200MeV 120 ～ 140MeV

60 ～ 120MeV 160 ～ 200MeV 3 ～ 40MeV 　 60 ～ 120MeV



Summary

• Collisions system dependence of Tch ,q

and s is less clear than dependence

•　 At SPS energies,

　　　 Chemical freeze-out temperature T

ch

> Tfo( ～ 140MeV)

s

Chemical freeze-out temperature and chemical potentials are extracted fromkaon and proton ratio in Pb+Pb collisions

Tch

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

kaon and proton ratios from central pb+pb collisions at the cern sps

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