Procedure for event characterization in Pb-Pb collisions at 40AGeV in the NA49 experiment at the CERN SPS

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.