Abstract
Results from the NA49 experiment at the CERN SPS are presented on event-by-event transverse momentum and multiplicity fluctuations of charged particles, produced at forward rapidities in central Pb+Pb interactions at beam momenta 20$A$, 30$A$, 40$A$, 80$A$, and 158$A$ GeV/c, as well as in systems of different size ($p+p$, C+C, Si+Si, and Pb+Pb) at 158$A$ GeV/c. This publication extends the previous NA49 measurements of the strongly intensive measure $\Phi_{p_T}$ by a study of the recently proposed strongly intensive measures of fluctuations $\Delta[P_T, N]$ and $\Sigma[P_T, N]$. In the explored kinematic region transverse momentum and multiplicity fluctuations show no significant energy dependence in the SPS energy range. However, a remarkable system size dependence is observed for both $\Delta[P_T, N]$ and $\Sigma[P_T, N]$, with the largest values measured in peripheral Pb+Pb interactions. The results are compared with NA61/SHINE measurements in $p+p$ collisions, as well as with predictions of the UrQMD and EPOS models.
Highlights
AND MOTIVATIONUltrarelativistic heavy-ion collisions are studied mainly to understand the properties of strongly interacting matter under extreme conditions of high energy densities when the creation of the quark-gluon plasma (QGP) is expected
A remarkable system size dependence is observed for both [PT,N ] and [PT,N ], with the largest values measured in peripheral Pb + Pb interactions
It is more limited for the analysis of the energy dependence since the same region was chosen at all energies [see lines in Fig. 1]
Summary
Ultrarelativistic heavy-ion collisions are studied mainly to understand the properties of strongly interacting matter under extreme conditions of high energy densities when the creation of the quark-gluon plasma (QGP) is expected. The present paper reports a continuation of this NA49 study by analyzing two new strongly intensive measures of event-by-event transverse momentum and multiplicity fluctuations, [PT ,N ] and [PT ,N ] [14,15]. These measures are dimensionless and have scales given by two reference values; namely they are equal to zero in the case of no fluctuations and equal to one in the case of independent particle production. The interpretation of the experimental results may benefit from a simultaneous measurement of both quantities
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