Abstract
The time evolution of the strongly interacting matter created in a heavy-ion collision depends on the initial geometry and the the centrality of the collision. Thus an experimental determination of the collision geometry is required. This paper discusses a procedure for event classification and estimation of the geometrical parameters in inelastic Pb+Pb collisions at a beam energy of 40A GeV recorded with the fixed target experiment NA49 at the CERN SPS. In the NA49 experiment, event classes can be defined using the measured multiplicity of particles in the Time Projection Chambers (TPC) or the energy of projectile spectators deposited in the forward Veto or Ring calorimeters. Using the Monte-Carlo Glauber model, these event classes can be related to average values of the geometric quantities such as impact parameter or number of nucleon-nucleon collisions. The implementation of this procedure within a software framework of the future CBM experiment was adopted for event classification in the NA49 experiment. In future, this procedure will be used for analysis of the new Pb+Pb data collected by the NA61/SHINE experiment and for comparison with the results previously obtained by STAR at RHIC and NA49 at the CERN SPS.
Highlights
IntroductionThe correlation between multiplicity Mtrk of produced particles and z-coordinate of the interaction vertex are shown in Fig. 2 (left)
The resulting one-dimensional distribution, which is shown on Fig. 2 for Mtrk ≤ 20, contains a signal from the Pb target, which is described by the Gaussian function, and for peripheral collisions a background, which is described by a polynomial of the first degree
The procedure for determining the geometric parameters of the collisions developed within the software framework of the future CBM experiment was adopted for event classification in the NA49 experiment
Summary
The correlation between multiplicity Mtrk of produced particles and z-coordinate of the interaction vertex are shown in Fig. 2 (left). The resulting one-dimensional distribution, which is shown on Fig. 2 (right) for Mtrk ≤ 20, contains a signal from the Pb target, which is described by the Gaussian function, and for peripheral collisions a background, which is described by a polynomial of the first degree. Using these functions, the signal function is fitted within 3 standard deviations from the peak value and the background function in the region near the collision vertex. In the projection for large multiplicity values there are no background events, so the EPJ Web of Conferences 182, 02132 (2018) ICNFP 2017
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