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NET CHARGE FLUCTUATIONS IN AA COLLISIONS IN A SIMPLE
STRING-INSPIRED MODEL
A.V. Titov 1† , V.V. Vechernin 1
(1) Saint Petersburg State University
† E-mail: arsenii.titov@gmail.com
Net charge fluctuations have been proposed as a possible indicator of the formation
of quark-gluon plasma in high-energy nucleus-nucleus collisions [1, 2]. The theoretical
predictions of the value of the fluctuations [1, 2, 3] do not directly consist with the experimental
results from RHIC [4]. At present the results extracted from ALICE experimental
data have also rather ambiguous interpretation in the framework of existing models [5].
In this connection, we try to describe the experimental data in the framework of an
alternative string-inspired model.
We introduce two effective sources of thehadron production. The first source emulates
the mid-rapidity particle production from the decays of the strings. In the string model
one has an approximate conservation of the charge locally in rapidity, so we assume this
source emits N 1+ positive and N 1− negative particles in the central rapidity interval ∆y
with the same mean values and variances, but due to “leakage” of the charge on the
borders of the interval N 1+ ≠ N 1− event-by-event. In string models the positive charge
of initial nuclear protons is associated with their valence quarks and is concentrated at
projectile and target rapidities. The transport of this charge into the mid-rapidity region
∆y is the second cause of the deviation of the charge from zero in this region. To simulate
this process we introduce the second source which produces only positive particles.
As a result the measure of the dynamical net charge fluctuations, ν dyn , is expressed in
terms of the model parameters. The parameters of the first (main) source are expressed
through the parameters characterizing the individual string and their event-by-event distribution.
The important feature of the model is that based on the results obtained in [6]
we do not assume that the engaged fluctuations are poissonian.
The model calculations are compared with the experimental data on pseudorapidity
dependence of ν dyn from RHIC [4]. It is shown that under some assumptions the obtained
results are consistent with the data.
References
[1] S. Jeon and V. Koch, Phys. Rev. Lett. 85, 2076 (2000).
[2] M. Asakawa, U. Heinz and B. Muller, Phys. Rev. Lett. 85, 2072 (2000).
[3] E.V. Shuryak and M.A. Stephanov, Phys. Rev. C 63, 064903 (2001).
[4] B.I. Abelev et al. (STAR Collaboration), Phys. Rev. C 79, 024906 (2009).
[5] S. Jena for the ALICE Collaboration, arXiv:1203.0542 [nucl-ex] (2012).
[6] V.V. Vechernin and H.S. Nguyen, Phys. Rev. C 84, 054909 (2011).
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