Quark Matter: Proceedings of the Sixth International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions — Quark Matter 1987 Nordkirchen, FRG, 24–28 August 1987

353 Pages·1988·10.333 MB·English

by  S. P. Sorensen (auth.), Professor Dr. Helmut Satz, Professor Dr. Hans Joachim Specht, Professor Dr. Reinhard Stock (eds.)

Quark Matter
Quark Matter
Proceedings of the
Sixth International Conference on Ultra-Relativistic
Nucleus-Nucleus Collisions - Quark Matter 1987
Nordkirchen, FRG, 24-28 August 1987
Editors: H. Satz, H.J. Specht, and R. Stock
With 320 Figures
Springer-Verlag Berlin Heidelberg New York
London Paris Tokyo
Professor Dr. Helmut Satz
Fakultat fiir Physik, Universitat Bielefeld, Postfach 8640
D-4800 Bielefeld, Fed. Rep. of Germany
Professor Dr. Hans Joachim Specht
1. Physikalisches Institut, Universitat Heidelberg, Philosophenweg 12
D-6900 Heidelberg, Fed. Rep. of Germany
Professor Dr. Reinhard Stock
Institut fiir Kernphysik, Universitat Frankfurt, August-Euler-Str. 6
D-6000 Frankfurt 90, Fed. Rep. of Germany
This book originally appeared as the journal
Zeitschrift f1ir Physik C - Particles and Fields, Volume 38, Number 1/2
(ISSN 0170-9739) © Springer-Verlag Berlin, Heidelberg 1988
ISBN-13: 978-3-642-83526-1 e-ISBN-13: 978-3-642-83524-7
DOl: 10.1007/978-3-642-83524-7
Library of Congress Cataloging-in-Publication Data. International Conference on Ultra-Relativistic Nucleus
Nucleus Collisions (6th: 1987 : Nordkirchen, Germany) Quark matter: proceedings of the Sixth International
Conference on Ultra-Relativistic Nucleus-Nucleus Collisions: quark matter, 1987, Nordkirchen, FRG, 24-28
August 1987/ editors, H. Satz, H.J. Specht, R. Stock. Published also as v. 38, no. 1/2 of the Zeitschrift fur Physik
C-Particles and fields. Bibiography: p. 1. Quarks-Congresses. 2. Hadrons-Congresses. 3. Heavy ion colli
sions-Congresses. I. Satz, H. II. Specht, H.J. (Hans Joachim), 1936-. III. Stock, R. (Reinhard), 1938-. IV.
Title. QC793.5.Q252I57 1987 539.7'21-dc 19 88-20011
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Contents
Preface. By R. Santo. H. Satz. H.J. Specht. R. Stock . 1
Oxygen-induced reactions at 60A GeVand 200A GeVstudied by calorimetry
By S.P. Sorensen et a!.. WA80 Collaboration (With 6 Figures) . 3
Transverse energy distributions in 160-nucleus collisions
By F. Corriveau et al.. HELlOS Collaboration (With 2 Figures) . 15
Study of the energy flow in 160-nucleus collisions at 60 and 200 GeV/nucleon
ByW. Heck et al.. NA35 Collaboration (With 14 Figures) . 19
Measurement of energy and charged particle emission in the central rapidity region from
O+A and p+A collisions at 14.5 GeV/c per nucleon and preliminary results from
Si +A collisions. By L.P. Remsberg et al.. E 802 Collaboration (With 12 Figures) . 35
Transverse energy distributions in Si-nucleus collisions at 10 Ge V/nucleon
By P. Braun-Munzinger et al.. E 814 Collaboration (With 7 Figures) . 45
Charged particle spectra in 160 induced nuclear collisions at the CERN SPS
By 1. Lund et a!.. WA 80 Collaboration (With 8 Figures) . 51
Measurement of multiplicity distributions in oxygentungsten collisions at 200 Ge V
per nucleon. By J. Schukraft (With 6 Figures) . 59
Review of high energy heavy ion reactions in emulsion. By I. Otterlund (With 13 Figures) . 65
First results from the hybrid emulsion experiment on 160-nucleus collisions at 200 Ge V/N
By L. Ramello (With 7 Figures) . 73
Pion interferometry with ultrarelativistic heavy-ion collisions from the NA 35 experiment
ByT.J. Humanic et al.. NA 35 Collaboration (With 5 Figures) . 79
Spectra of negative particles and photons in collisions of p-W and loO_W at 200 Ge V/u
By H.-W. Bartels (With 3 Figures) . 85
Negative particle production in nuclear collisions at 60 and 200 Ge V/nucleon
By H. Strbbele et al.. NA 35 Collaboration (With 11 Figures) . 89
Neutral transverse momentum spectra in 60 and 200A· GeVl60 + nucleus and
proton + nucleus reactions. By H. Lbhneret al .. WA 80 Collaboration (With 8 Figures) . 97
Transverse momentum systematics in proton-proton and light ion collisions at the ISR
By H.G. Fischer (With 7 Figures) . 105
Target fragmentation in proton-nucleus and 160-nucleus reactions at 60 and 200 GeV/nucleon
By H.R. Schmidt et al.. WA 80 Collaboration (With 12 Figures) . 109
The production of JIIJf in 200 GeV IA oxygen-uranium interactions
By A. Bussiere et al.. NA38 Collaboration (With 11 Figures) . 117
First results on strangeness production in 60 and 200 Ge V/nucleon heavy ion reactions
from the NA 35 streamer chamber
By G. Vesztergombi et a!.. NA 35 Collaboration (With 5 Figures) . . 129
Astudy of 1f and K production in proton-uranium and oxygen-uranium interactions
at 200 GeVIA using decay muons
By P. Sonderegger et al.. NA 38 Collaboration (With 18 Figures). 133
Preliminary spectrometer results from E-802
ByY. Miake et al.. E802 Collaboration (With 5 Figures) . 135
The QCD vacuum and quark-gluon plasma. By E.V. Shuryak (With 5 Figures). 141
Lattice QCD at finite temperature: a status report. By F. Karsch (With 10 Figures) . 147
Connection between perturbation theory and lattice QCD. By K. Kajantie (With 3 Figures) 157
On a non-perturbative pressure effect in lattice QCD
By M.l. Gorenstein. O.A. Mogilevsky (With 2 Figures). 161
The '"instanton liquid"". By E. V Shuryak (With is Figures) . 165
Quarks and gluons in colour fields. By A. Bialas. W. Czyz (With 6 Figures) . 173
A unified approach for hadronic and nuclear collisions: the dual parton model
By A. Capella. J. Tran Thanh Van (With 16 Figures) . 177
The materialization phase in the colour rope picture. By J. Knoll (With 4 Figures) . 187
Ultra-relativistic heavy ion collisions in a multi-string model. By K. Werner (With 6 Figures) 193
Multiplicity distributions in hadronic and heavy ion reactions. By R.M. Weiner 199
The approach to equilibrium in a quark-gluon plasma. By U. Heinz. 203
Gluon transport equations. plasma oscillations. and screening. By H.-Th. Elze . 211
Central region in relativistic heavy ion collisions; results from hydrodynamic calculations
and cascade simulation. By P. V Ruuskanen (With 12 Figures) . 219
Initial state formation in the hydrodynamical theory of nucleon-nucleon collisions
By E.L. Feinberg. 229
Rapidity distributions and energy densities from hydrodynamical studies at 5-200 GeV/n
ByT. Rentzsch. G. Graebner. J.A. Maruhn. H. Stocker. W. Greiner (With 14 Figurcs) . 237
JllJf Suppression by plasma formation. ByT. Matsui (With 1 Figurc) . 245
Mass shifts of charmoniums and electromagnetic signals
ByT. Hashimoto. K. Hirose. T. Kanki. O. Miyamura (With 3 Figures) 251
Searching photon signal of quark-gluon plasma formation
ByVV. Goloviznin. A.M. Snigirev. G.M. Zinovjev. 255
Quark-matter diagnostics: dileptons. photons and (J/lfI) suppression
By B. Sinha (With 6 Figures) . 259
Perturbative aspects of dilcpton production at finite temperature
By R. Baier. B. Pire. D. Schiff (With 1 Figure) . 265
Strong interacting probes for quark gluon plasma. By P. Koch (With 3 Figures) . 269
/1(/1) Longitudinal polarization: a signature for the formation of a quark-gluon plasma
in heavy ion collisions. By M. Jacob. 273
Enhanced multiplicity fluctuation as a possible signature of quark matter. By R.C. Hwa . 277
Emission of droplets of strange quark matter in RHIC
By C. Greiner. D. Rischke. H. Stocker. P. Koch (With 10 Figures) . 283
Dense nuclear matter: supernovae and heavy ions. By G.E. Brown (With 10 Figures) 291
Quark matter in astrophysics and cosmology. By A. V Olin to (With 3 Figures) 303
Hadron-quark phase transition in dense stars. By F. Grassi (With 4 Figures) . 307
The EMC effect - status and perspectives. By K. Rith (With 6 Figures) . 317
The ion programme at CERN: a brief outline. By P. Darriulat. 325
Lead beam experiments at the CERN SPS. By A. Sandoval (With 10 Figures) . 329
The time projection chamber for heavy-ion collisions: trends and perspectives
By F. Sauli (With 22 Figures) . 339
The relativistic heavy ion collider project: a status report
By T. W. Ludlam. N .P. Samios (With 6 Figures) . 353
Quark Matter 1987: concluding remarks. By M. Gyulassy . 361
Preface
This volume contains the papers which have been presented at the Sixth International
Conference on Ultra-Relativistic Nucleus-Nucleus Collisions, Quark Matter 1987, held
in Nordkirchen from August 24-28, 1987.
The conference was attended by about 250 scientists, representing 75 research
institutions around the world - the scientific community engaged in experimental
and theoretical studies of high energy nuclear collisions. The central theme of the
meeting was the possibility of achieving extreme energy densities in extended systems
of strongly interacting matter - with the ultimate aim of creating in the laboratory
a deconfined state of matter, a state in which quarks and gluons become the active
degrees of freedom. High energy accelerator beams and cosmic radiation projectiles
provide the experimental tools for this endeavor; on the theoretical side, it is intimate
ly connected to recent developments in the non-perturbative study of quantum chro
modynamics. Phase transitions between hadronic matter and quark-gluon plasma
are of basic interest also for our understanding of the dynamics of the early universe;
they may be relevant for the behaviour of neutron stars, or even for the structure
of certain exotic astrophysical objects, such as Cygnus X.
A very special aspect of this Sixth Quark Matter Conference was the advent
of the first experimental results from dedicated accelerator studies. These were con
ducted during 1986/87 at the AGS of Brookhaven National Laboratory, with beams
of 160 and 28Si at 14 GeV/nucleon, and at the CERN SPS, with 160 at 60 and
200 GeV / nucleon. An intense discussion of these data formed the main activity of
the meeting. Despite some hints in the right direction, it is still too early to reach
any conclusions about actual quark-gluon plasma formation. It did become clear,
however, that the experimental techniques are suitable for measuring the relevant
observables, and it seems possible to attain in nuclear collisions energy densities
sufficient for plasma production.
For the convenience of the reader, we have grouped the written versions of
the talks according to their subject matter, and not in the order in which they
were presented at Nordkirchen. We are grateful to all contributors for their efforts
in providing the manuscripts - in particular to the experimental groups who were
left with little time between first data taking and publication. Some of the contribu
tions therefore still retain a certain preliminarity; but perhaps this will co very to
the reader some of the excitement felt by the participants as they had their first
look at a so far unexplored area of physics.
In closing we want to thank the members of our International Advisory Commit
tee for their assistance, and the entire organisational staff of the meeting who worked
so hard in making Quark Matter 1987 a success.
March 1988 R. Santo, H. Satz, H.J. Specht, R. Stock
(Organizing Committee)
Oxygen-induced reactions at 60 A GeV and 200 A GeV
*
studied by calorimetry
S.P. Sorensen
University of Tennessee, Knoxville, and Oak Ridge National Laboratory, Oak Ridge, USA
W A 80 Collaboration
R. Albrecht,3 T.e. Awes/ e. Baktash/ P. Beckmann,4 F. Berger,4 R. Bock,3 G. Claesson,3 L. Dragon,4
R.L. Ferguson,2 A Franz,5 S. Garpmann,6 R. Glasow,4 H.A Gustafsson,6 H.H. Gutbrod,3 K.H. Kampert,4
B.W. Kolb,3 P. Kristiansson,5 LY. Lee,2 H. Lohner,4 L Lund,3 F.E. Obenshain,1.2 A Oskarsson,6
L Otterlund,6 T. Peitzmann,4 S. Persson,6 F. PlasiI,2 AM. Poskanzer,s M. Purschke,4 H.G. Ritter,5 R. Santo,4
H.R. Schmidt,3 T. Siemiarczuk,3.a S.P. Sorensen,1,2 E. Stenlund,6 G.R. Young 2
1 University of Tennessee, Knoxville, TN 37996, USA
2 Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
3 Gesellschaft fUr Schwerionenforschung (GSI), D-6100 Darmstadt, Federal Republic of Germany
4 University of Munster, D-4400 Munster, Federal Republic of Germany
5 Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA
6 University of Lund, S-22362 Lund, Sweden
Abstract. Results based on calorimetric measurements trum of possible plasma signatures has been suggested
are presented from reactions of 60 A Ge V and 200 A [1,2]. An unfortunate common characteristic of most
GeV 160 projectiles with C, Cu, Ag, and Au nuclei. of these signatures is the necessity to distinguish them
Minimum-bias cross sections are discussed. Energy from the background created by nonplasma events.
spectra measured at zero degrees and transverse-ener A thorough understanding of the reaction mecha
gy distributions for the pseudo rapidity range 2.4 ~ fJ ::s;; nisms in ultrarelativistic heavy ion collisions is, there
5.5 are shown. An analysis of the average transverse fore, an important prerequisite in any QGP search.
energy in terms of the number of participating nucle This paper presents some of the first steps taken in
ons and the number of binary nucleon-nucleon col this direction by the W A 80 collaboration. The focus
lisions is presented. Estimates of nuclear stopping and will be on data obtained with our calorimeters, with
of attained energy densities are made. special emphasis on the results which can be extracted
from forward calorimetry.
In an effort to isolate characteristic features of
nucleus-nucleus collisions (e.g., collective phenomena)
from those that may be expected on the basis of a
1 Introduction
linear superposition of nucleon-nucleon collisions, we
The study of heavy ion collisions at ultrarelativistic
will compare measured quantities with calculations
energies is a new and exciting field on the borderline
that reproduce data from nucleon-induced reactions
between nuclear and high energy physics. Presently,
and that make predictions for nucleus-nucleus reac
the primary goal is to verify the existence of the postu
tions. While several models are available for this pro
lated quark-gluon plasma (QGP) [1]. A broad spec- cedure, none has yet been demonstrated to have clear
advantages over the others. Consequently, we have
Presented at the 6th International Conference on Ultra-Relativistic
Nucleus-Neucleus Collisions - Quark Matter 1987, 24--28 August chosen to make comparisons with the Lund model
1987, Nordkirchen, Federal Republic of Germany for high-energy nucleus-nucleus interactions (FRI
a On leave of absence from the Institute for Nuclear Studies, War TIOF) [3]. Effects of detector acceptance and of trig
saw, Poland ger bias have been included in all FRITIOF simula-
4
tions shown in this work except for the total reaction to I] > 6.0. The ZDC is both a key component of the
cross section calculations. In describing the nuclear trigger system and an important measuring device
density, the radius parameter ro = 1.10 fm has been from which the total energy of projectile spectators
used for the Woods-Saxon distributions. This results and/or of the leading particles is obtained. The resolu
in somewhat larger sizes of the light nuclei as com tion of the ZDC is 2.5% at 3.2 TeV and 4.5% at
pared to the standard FRITIOF parameter selection 0.96 TeV.
but is in better agreement with results for the nuclear All data presented in this paper were obtained
density distribution from electron scattering [4]. under the minimum-bias condition. This condition
Another theme in our current analysis is the ex is defined by the requirements that: (a) less than 88%
traction of results from the data with minimal use of the full projectile energy is measured by the ZDC
of complicated models. Some reliance on models is, and (b) at least one charged particle is recorded by
however, needed in any interpretation of experimental the multiplicity arrays in the interval 1.3 < I] < 4.4.
data. An analysis of the transverse energy generated
in terms of the number of participating nucleons and
3 Reaction cross sections
the number of binary nucleon-nucleon collisions will
be presented in Sect. 6. Although the extraction of Usually the first quantities to be measured in a new
these numbers is not model-independent, it is based field of nuclear physics are the reaction cross sections.
primarily on simple geometrical aspects of the nuclear We will not deviate from this practice and present
collisions. in Table 1 the measured minimum-bias cross sections,
Finally results on nuclear stopping and energy together with two sets of FRITIOF calculations: the
densities are presented in Sect. 7 and 8, respectively. total reaction cross section based on the requirement
that at least one nucleon from the projectile collides
with a target nucleon, and the minimum-bias cross
2 Experimental setup
sections, based on simulated trigger constrains in the
The measurements described in this paper were per FRITIOF-generated events. Systematic errors on the
formed with the W A 80 experimental arrangement [5, absolute cross sections are estimated to be less than
6J at the CERN SPS. The setup includes two calorim 10%. FRITIOF reproduces both the energy and the
eters: the Mid-Rapidity Calorimeter (MIRAC) and target dependence of the measured minimum-bias
the Zero-Degree Calorimeter (ZDC) [7]. MIRAC con cross sections also to within 10%.
sists of 30 stacks with each stack subdivided into six
20 x 20 cm2 towers. Each tower consists of a lead/scin
tillator electromagnetic section of 15.6 radiation
Table 1. Reaction cross sections. Systematic errors on the experi-
lengths (0.8 absorption lengths) and an iron/scintillator
mental cross sections are estimated to less than 10%. Please refer
hadronic section of 6.1 absorption lengths. MIRAC is to the next for the definition of the minimum-bias condition. ro
organized into five groups of six stacks, called six and b are fitted Bradt-Peters parameters
packs, each with dimensions of 1.3 x 1.2 m2• Four ofthe
six-packs are arranged in a wall around the beam E1ab=60 A GeV min bias min bias reaction
axis at a distance of 6.5 m from the target and with a O'EXP (JFRITIOF (JFRITIOF
[mb] [mb] [mb]
7.5 x 7.5 cm2 hole in the center to allow the beam
to reach the ZDC. The MIRAC wall has full azimuth 160+ 12C 650 650 1100
al coverage in pseudo rapidity, 1], from 2.4 to 5.5 with 160+65CU 1650 1440 2100
160+ 108Ag 2250 1950 2630
partial coverage extending down to 2.0. The fifth six
160+197Au 2900 2660 3360
pack of MIRAC is placed next to the MIRAC wall,
ro [fm] 1.46 1.32 1.26
where it covers approximately 10% of the azimuthal
b[fm] -2.34 -1.82 -0.08
angles in the pseudo rapidity interval from 1.6 to 2.4
The measured (J/E resolutions of the calorimeter are
14.2% for 10 GeV/c charged pions and 5.1% for E1ab = 200 A GeV min bias min bias reaction
10 GeV/ c electrons [7]. O'EXP (JFRITIOF O'FRITIOF
[mb] [mb] [mb]
The ZDC is a 60 x 60 cm2 uranium/scintillator
calorimeter divided into an electromagnetic section 160+12C 450 460 1100
of 20.5 radiation lengths and a hadronic section of 160+65CU 1350 1270 2100
9.6 absorption lengths. The ZDC is located 11 m from 160+ 108Ag 1800 1660 2630
160+197Au 2450 2290 3360
the target and measures the energy of particles that
pass through the beam hole in MIRAC. This hole ro [fm] 1.44 1.41 1.26
b[fm] -3.02 -2.92 -0.08
has an inscribed cone angle of 0.3 deg, corresponding
5
The target dependence is given approximately by metrical considerations can be used as a key for a
the sum of the transverse areas of the nuclei as ex qualitative understanding of the ZDC energy spectra
pressed in the Bradt-Peters parametrization [8J shown as filled circles in Fig. 1. At 200 A GeV, the
160 + 12C reaction has essentially no cross section
(1) for events depositing a small amount of energy in
the ZDC because, in a simple participant spectator
The radius parameter, ro, and the overlap parameter
picture, even in the most central collisions, several
b extracted from the At dependence of the cross sec
projectile spectator nucleons, each with an energy of
tions are also shown in Table 1. It is noteworthy that
200 GeV, proceed in the beam direction. In contrast,
the overlap parameter for the FRITIOF total reaction
a pronounced peak is seen at small ZDC energies
cross sections is practically zero, whereas the mini in the spectrum from the 160 + 197 Au reaction. In
mum-bias cross sections show a large negative value
this case, events with low ZDC energies result from
of b. This indicates that b is to a larger extent a mea
central collisions in which the oxygen projectile is
sure of the trigger bias in this experiment than an
engulfed by the massive Au nucleus, resulting in the
estimate of the overlap between two nuclei in reac
emission of only a few leading particles at angles less
tions where at least one nucleon-nucleon collision
than 0.3 deg. Furthermore, in this case, a wide range
takes place.
of impact parameters gives rise to collisions in which
While the calculated reaction cross sections show
the entire projectile interacts with a nearly constant
no energy dependence, the minimum-bias cross sec
number of target nucleons, thus producing the peak
tions show a strong energy dependence. This depen
at low ZDC energies.
dence originates from different acceptances of the
The effects of the more restricted acceptance of
minimum-bias trigger at the two beam energies and
the ZDC in going from 200 A GeV to 60 A GeV,
can be understood from the following argument.
as discussed above, is clearly seen in the 60 A GeV
In a reaction with a given impact parameter the 160 + 197 Au spectrum, which has an even more pro
ratio between the energy deposited in the Zero-De
nounced peak at the lowest energies. In the 60 A GeV
gree Calorimeter, EZDO and the beam energy, Ebeam, 160 + 12C reaction there are many more events with
can be expressed as
low ZDC energies as compared to the 200 A GeV
case. These events may originate from collisions in
(2) which the oxygen projectile fragments so violently
that one or more of the projectile spectators has a
pseudorapidity lower than 6 and is thereby inter
where Es p is the energy carried by the projectile spec
cepted by MIRAC.
tators, and E is the reaction energy or, equivalent
reac
The predictions of the FRITIOF model are shown
ly, the energy carried by the projectile participants,
as histograms in Fig. 1. The agreement with the data
and E (1J > 6) is the reaction energy accepted by
reac
is generally better at 200 A GeV than at 60 A GeV.
the 0.30 beam hole in MIRAC. In going from 60 A
There is a clear tendency for FRITIOF to underesti
GeV to 200 A GeV, the nucleon-nucleon CM rapidity
increases from 2.4 to 3.0. As a consequence, if there mate the cross section for small values of EZDC• This
could indicate that FRITIOF does not include a suffi
is no significant change in the reaction mechanism,
ciently large degree of longitudinal momentum
E (1J> 6) will constitute a larger fraction of E
reac reac
transfer in binary nucleon-nucleon collisions, but a
at the higher bombarding energy and Esp will, there
final conclusion on this point will have to wait until
fore, have to constitute a smaller fraction of E
beam
the nuclear density prescription in FRITIOF has been
in order to fulfill the most stringent of the trigger
requirements, namely EZDC < 0.88 * Ebeam. Smaller further evaluated.
values of Esp/Ebeam implie smaller impact parameters
and, thereby, smaller total minimum-bias cross sec 5 Transverse energy distributions
tions at the higher beam energy.
The transverse energy produced in the reaction is
measured on an event-by-event basis in MIRAC. The
transverse energy is calculated as ET = I: Ei sin(Oi),
4 Zero-degree energy distributions
where Ei and 0i are the observed energy and the effec
An important aspect of high energy nucleus-nucleus tive angle of each element i of MIRAC, respectively.
collisions is the nuclear collision geometry [9-11 J as The estimated systematic error in the transverse ener
determined by the relative sizes of the target and pro gy scale is less than 10%. Based on measurements
jectile nuclei, the overlap volume in the collision, and of the response of the calorimeter to electrons, pions,
the impact parameter. As a consequence, simple geo- and protons of known energies between 2 and
6
60 A GeV 200 A GeV
c C 0.8
2.4
1.2
0.0
3 Cu Cu 1.5
:>
2 1.0
Q)
-0-
-.ED 1 .... ... ..+ ::!,"""'~~ 0.5
0 f+:.!.! :. .L---1.-L-.....L.---l'--'----1.-+-J 0.0
5
Ag Ag
() ... 1.5
~4 ...
W
-- 3 1.0
'0 ....... ........
\:) 2
'0 0.5
o
8 Au
1.5
6
1.0
4
... Fig. 1. Energy spectra measured in the Zero-Degree
0.5 Calorimeter (filled circles) in 160 induced reactions .
2
Histograms give the results of the FRITIOF model
o '-'---'---'--'--'--'----'---'.-.J 0.0 [3]. The vertical error bars represent statistical errors
o 200 400 600 800 o 1000 2000 3000
E
ZDC (GeV)
50 GeV, an iterative procedure has been developed a nearly constant number of target nucleons. As the
by means of which the nonprojective features of the target becomes smaller, the peak and the plateau be
calorimeter response are corrected for. The method come less pronounced. For 160 + 12C, the ET spectra
is described in detail elsewhere [7, 12]. have shapes similar to those of the ET spectra mea
The transverse energy distributions for sured in proton-induced reactions [13], whereas the
2.4 < '1 < 5.5 are shown as filled circles in Fig. 2. As heavy target spectra are similar, both in shape and
in the case of the ZDC spectra, the shapes of the energy scale, to the ET spectra for 200 A GeV 160
ET spectra are dominated by effects of the nuclear + Pb of the NA 35 collaboration [10].
geometry. The spectra for the heaviest nuclei, Ag and At 60 A GeV, the high-energy tails of the ET distri
Au, show a large "plateau" extending out to 80- butions for Cu, Ag, and Au targets almost coincide
100 GeV at 200 A GeV beam energy and to 40- with one another at a value of approximately 60 GeV.
45 GeV at 60 A GeV. The Au spectra have a broad This phenomenon could be caused by "complete
peak at the high-energy end of the plateau. This peak stopping" as discussed by the E802 collaboration for
is closely correlated with the low-energy peak in the data obtained at 15 A GeV [14]. However, at our
Au ZDC spectra [9]. This correlation demonstrates beam energies, this finding is more likely to be due
that the peak in the ET distribution, corresponding to a combination of two opposing effects. As the tar
to low ZDC energies, originates from the most central get mass or number of target participants increases,
collisions, in which the entire projectile interacts with the maximum transverse energy increases. At the