Indian J. Phys. 84 (6), 757-761 (2010) © 2010 IACS Variation of multiplicities of the secondary charged particles on the geometry of collision R Talukdar, S Sengupta, B Debnath and B Bhattacharjee* Department of Physics, Gauhati University, Guwahati- 781 014, Assam, India E-mail: bb_22@rediffmail.com Abstract : The total charge of the projectile spectator fragments, Q pf is taken as a measure of the degree of centrality of collision thus defining the collision geometry. In this paper the mean multiplicities of the different charged secondaries emitted in the interaction of 24 Mg-Em at 4.5A GeV have been investigated as a function of the total charge Q pf of the projectile spectator fragments. It has been observed that the average number of the produced particles, <N s > and the heavily ionizing particles, <N h > decreases exponentially with the increase of Q pf showing strong correlation with the geometry of the collision. An attempt has also been made to compare these results with 84 Kr-Em interaction at 0.95A GeV. Keywords: Nucleus-Nucleus collision, Collision geometry, multiplicity PACS Nos. : 25.75.-q, 25.70.Pq, 13.85.Hd 1. Introduction According to participant spectator model [1] the interacting system in high energy nucleus- nucleus collision can be divided into three parts: a target spectator, a participant and a projectile spectator. The overlapping part of the two colliding nuclei is called the participant, and the non-overlapping portion of target and projectile nuclei are respectively called the target and projectile spectators. The model predicts that violent nucleon-nucleon collision takes place in the participant region and weak excitations and cascade collision takes place in the spectator parts. The participants produce many mesons, nucleons, photons, lepton pairs etc., and the spectators break into many nucleons and nuclei. There are relations between the participants and the spectators. Relativistic nucleus-nucleus collisions are the unique tool to produce and study dense nuclear matter in the laboratory [2-4]. From straightforward geometrical considerations, *Corresponding Author