particle ratios from central pb+pb collisions at the cern sps

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 Pt

Chemical property

Thermal freeze-out

③ Summary

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INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997

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

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

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INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997

•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

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INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997

Masashi Kaneta / Hiroshima univ. 5

INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997

PID

• Selection between K and p

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INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997

NA44 acceptance

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INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997

Selection of centrality

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INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997

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.

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INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997

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

pass p,p,, through NA44 detectors

Example of Pt distribution

dN/dy: ±30%mt slope: ±10%As systematic error {

Correction factor for p/p ratio

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INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997

Strangeness neutral hadron gas

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INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997

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 y1.6.

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INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997

Comparison with model prediction

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INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997

Thermal freeze-out temperature

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INTERNATIONAL SYMPOSIUM ON STRANGENESS IN QUARK MATTER 1997

SummarySummary

•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

TemperatureTemperature TTch ch ~ 175MeV~ 175MeV

Chemical potentialChemical potential

qq ~ 80MeV, ~ 80MeV, ss ~ 30MeV ~ 30MeV

TTchch T Tf0f0

In Pb+Pb central collisions