Maximum fluctuations of charged particle densities in narrow pseudorapidity space
at ultrarelativistic nuclear collisions
Dipak Ghosh, Argha Deb, Jayita Ghosh, Rini Chattopadhyay, Madhumita Lahiri, Abdul Kayum Jafri, Sunil Das,
and Md. Azizar Rahman
High Energy Physics Division, Jadavpur University, Calcutta-700032, India
Received 7 February 2000; published 2 August 2000
A study of multiparticle correlations on the basis of the maximum fluctuation of the charged particle density
in narrow pseudorapidity intervals in Monte Carlo background particles has been carried out with
16
O-AgBr
interactions at 60A GeV and
32
S-AgBr interactions at 200A GeV. The study reveals the existence of dynamical
multipion correlation in the pseudorapidity interval 0.1–1 for both data sets. Further study suggests that in each
case the maximum charged particle density in a given pseudorapidity interval increases linearly with charged
particle multiplicity.
PACS numbers: 25.75.Gz, 25.70.Pq, 24.60.Ky
Nowadays, various theoretical models 1 have been put
forward to understand the underlying dynamics of multipion
production in hadron-hadron, hadron-nucleus, and nucleus-
nucleus collisions at relativistic and ultrarelativistic energies.
Experimental evidence shows that the produced particles
prefer to be emitted in a correlated fashion 2. The reason
for such a correlation effect, explained by different theorists,
may be the production of resonance phenomena, hot multi-
nucleon fireballs, or the formation of a quark-gluon plasma,
etc. Study of the experimental data 3 prompted the scien-
tists to conclude that the formation of heavier intermediate
states, clusterization, etc., may be the cause of such a corre-
lation effect. So a detailed study on the correlation and clus-
terization of secondary particles in multiparticle production
processes is needed to extract the actual reason behind such
an effect. Very recently, the intermittent behavior of the mul-
tiplicity fluctuation 4,5 has also been interpreted by some
workers to be the possible manifestation of such a short
range correlation in high-energy interactions. Whatever may
be the reason for such phenomena, it had recently been felt
strongly that the commonly used method of the standard cor-
relation function is not sufficient enough to come to a con-
clusion beyond ambiguity. So the need for an in-depth analy-
sis in this field has arisen.
In this paper we will study multiparticle correlation phe-
nomena of the produced pions on the basis of the maximum
density fluctuation of the charged particles in narrow pseu-
dorapidity intervals. Though several studies 6–10 in this
field have been reported for hadron-hadron, hadron-nucleus,
and low energy nucleus-nucleus interactions, up to now no
detailed analysis of such phenomena has been carried out at
ultrarelativistic nuclear collisions. Data of
16
O-AgBr interac-
tions at 60A GeV and
32
S-AgBr interactions at 200A GeV are
used here for the analysis.
The details of the exposure of the plates, scanning of
events, angle measurement, etc., are given in Refs. 11,12.
In this paper we adopted the method as followed by Sarki-
syan et al. 13. For each event the ordered pseudorapidity
=-ln tan /2 is the emission angle of the particle is
scanned, with a fixed pseudorapidity window/bin across
the full range of the event. The maximum density of par-
ticles as defined by 13 is equal to
max
=n
max
/, where
n
max
is the maximum number of particles within the inter-
val in each event.
max
for all N events is then calculated
and the distribution dN / d
max
with respect to
max
is ana-
lyzed. The same procedure has been followed with the cor-
relation free events generated by Monte Carlo simulations.
The Monte Carlo data are generated following the assump-
tions: i The pions are emitted independently. ii The mul-
tiplicity distribution of the ensemble of the Monte Carlo
events is the same as the multiplicity spectrum of the experi-
mental ensemble. iii The single-particle spectrum d / d
of the simulated interactions reproduces the experimental
d / d distribution.
The distribution dN / d
max
with experimental data sets
and ( dN / d
max
)
MC
with Monte Carlo–simulated data sets
of
16
O-AgBr interactions at 60A GeV for window
FIG. 1. Plot of the normalized
max
distribution for
16
O-AgBr
interactions at 60A GeV in pseudorapidity windows =a 0.1,
b 0.5, c 0.8, and d 1, respectively.
PHYSICAL REVIEW C, VOLUME 62, 037902
0556-2813/2000/623/0379023/$15.00 ©2000 The American Physical Society 62 037902-1