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 PT
Chemical property
③ Chemical freeze-out
④ Thermal freeze-out
⑤ Summary
International School on the Physics of Quark Gluon Plasma
June 3-6, 1997, Hiroshima
Motivations
• Particle ratios
– Sensitivity to collision dynamics
– Check chemical equilibrium assumption
A Scenario
E x p ansi
on
Collisions
Masashi Kaneta / Hiroshima univ.
Chemical freeze-out？
Thermal freeze-out
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International School on the Physics of Quark Gluon Plasma
June 3-6, 1997, Hiroshima
The NA44 Collaboration
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, A.G. Hansen1,O. Hansen1, D. Hardtke8, H. van Hecke2,
E.B. Holzer9, T.J. Humanic8, P. Hummel9, B.V. Jacak2, R. Jayanti8,
M. Kaneta5, M. Kopytine2, M. Leltchouk3, A. 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, D. Reichhold8, 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
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.
A
Now at Universität Heidelberg, Physikalisches Institut, 69120 Heidelberg, Germany.
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.
B
Masashi Kaneta / Hiroshima univ.
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International School on the Physics of Quark Gluon Plasma
June 3-6, 1997, Hiroshima
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 ( ylab 3 )
 0  PT 1.6 GeV/c
 TOF resolution  100ps
 dP/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
Masashi Kaneta / Hiroshima univ.
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International School on the Physics of Quark Gluon Plasma
June 3-6, 1997, Hiroshima
Masashi Kaneta / Hiroshima univ.
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International School on the Physics of Quark Gluon Plasma
June 3-6, 1997, Hiroshima
PID
• Selection between K and p
Masashi Kaneta / Hiroshima univ.
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International School on the Physics of Quark Gluon Plasma
June 3-6, 1997, Hiroshima
NA44 acceptance
Masashi Kaneta / Hiroshima univ.
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International School on the Physics of Quark Gluon Plasma
June 3-6, 1997, Hiroshima
Selection of centrality
Masashi Kaneta / Hiroshima univ.
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International School on the Physics of Quark Gluon Plasma
June 3-6, 1997, Hiroshima
Ratios as a function of PT and centrality
† Those ratios are measured downstream (~20m) from
collision point.
 The feed-down from resonance is included in it.
Lcorrection factor for p/p: 0.9 ± 0.1
Masashi Kaneta / Hiroshima univ.
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International School on the Physics of Quark Gluon Plasma
June 3-6, 1997, Hiroshima
Strangeness neutral hadron gas
Masashi Kaneta / Hiroshima univ.
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International School on the Physics of Quark Gluon Plasma
June 3-6, 1997, Hiroshima
Comparison ratios with model prediction
Masashi Kaneta / Hiroshima univ.
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International School on the Physics of Quark Gluon Plasma
June 3-6, 1997, Hiroshima
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
Masashi Kaneta / Hiroshima univ.
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International School on the Physics of Quark Gluon Plasma
June 3-6, 1997, Hiroshima
Thermal freeze-out
1 dN
mT
 A exp( 
)
mT dmT
T
: Boltzmann distribution
Transverse mass distributions
(a) Positive
(b) Negative
The dashed lines
in figure are
fits to the function
Phys. Rev. Lett.
78 (1996) 2080
• The slope parameter T depends on particle mass
Masashi Kaneta / Hiroshima univ.
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International School on the Physics of Quark Gluon Plasma
June 3-6, 1997, Hiroshima
Thermal freeze-out temperature
• Slope parameter T and particle mass m may be
described by the relation ship
T = Tfo + m<vt>2
• Tfo : freeze-out temperature
• <vt> : averaged collective flow velocity
Phys. Rev. Lett.
78 (1996) 2080
At SPS
Tfo = 140±10 MeV
At AGS
Tfo = 145±15 MeV
Masashi Kaneta / Hiroshima univ.
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International School on the Physics of Quark Gluon Plasma
June 3-6, 1997, Hiroshima
Summary
In Pb+Pb central collisions from SPS
• 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
 Temperature
Tch ~ 175MeV
 Chemical potential mq ~ 80MeV, ms ~ 30MeV
 Tch > Tf0
Chemical freeze-out and
Thermal freeze-out temperatures
Tch
[MeV]
Tfo [MeV]
SPS:
170～210
140±10
AGS:
130～150
145±15
Masashi Kaneta / Hiroshima univ.
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International School on the Physics of Quark Gluon Plasma
June 3-6, 1997, Hiroshima
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
Example of Pt distribution
pass p,p,L,L through NA44 detectors
Correction factor for p/p ratio
As systematic error
Masashi Kaneta / Hiroshima univ.
{
dN/dy: ±30%
mt slope: ±10%
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International School on the Physics of Quark Gluon Plasma
June 3-6, 1997, Hiroshima
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)
Kaons
: ratios around the mid rapidity
is the same with absolute ratio.
protons
: both ratios are close
in the region dy1.6.
Masashi Kaneta / Hiroshima univ.
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