Scaling of multiplicity distribution in high energy hadron-nucleus interactions

Abstract

Analysis of 50 and 340 GeV pion-nucleus and 400 GeV proton- nucleus interactions data for multiplicity scaling study has been carried out. The multiplicity distribution of compound(sum of shower and grey particles in an event), slow (black tracks) particles and target protons ( grey tracks) are found to obey a KNO type scaling law. Keywords: Multiplicity scaling, compound multiplicity, relativistic charged particles, multiparticle production, multiplicity distribution Subject classification PACS 13.85 - Hadron - induced high - and superhigh - energy interactions, energy > 10 GeV. I. Introduction During the last many years, the work on high energy experiments was carried out by several workers(1-8) mostly for shower particles which are fast moving charged particles or we can say that relativistic charged particles in hadron-nucleus (hA) and nucleus-nucleus (AA) collisions. The investigation of hA collisions is fundamental for understanding the nature of the interaction process. It is believed that these interactions may provide some very useful information about the dynamics of multiparticle production. An important feature noticed in these interactions is that the nucleus plays the role of target for the incident hadron. For the present study nuclear emulsion technique has been used to collect the data. Nuclear emulsion is a material which memorises the tracks of charged particles. When a particle, let us call it as a primary particle, is incident on the nuclei of the emulsion, secondary particles are produced in the form of tracks. These particles are termed as shower, grey and black particles; and their number in an event/interaction is given as ns, ng and nb. We have tried to study the compound particle (nc) multiplicity distribution also. A compound particle is defined as the sum of number of shower (ns) and grey (ng) particles in an event, i.e., nc=ns+ng. The study on compound particle multiplicity was first done by Jurak and Linscheid (9). We studied some aspects of compound multiplicity distribution in our earlier publication (10), this paper is in continuation to that (10). Many workers (12-20) have studied various characteristics of compound multiplicity distributions for high energy interactions. An attempt has also been made to study the multiplicity distributions of the slow particles (black tracks) and target protons (grey particles). In the present paper an effort is made to test the validity of hypothesis of Koba, Neilsen and Olesen (11) which is referred to as KNO scaling in the case of compound as well as slow particles. II. Experimental details In order to collect the experimental data, a stack of Ilford-G5 emulsion pellicles exposed to a 340 GeV negative pion beam was used. The events/interactions were picked up after leaving 3 mm from the leading edges of the pellicles to avoid any distortion effects. The measurement was carried out using an oil immersion objective of 100X magnification. To rule out any contamination of primary events with secondary interactions, the primaries of all the events were followed back up to the edge of the plates and only those events whose primary remained parallel to the main direction of the beam and which did not show any significant change in their ionization were finally picked up as genuine primary events. In these interactions the secondary particles appear in the form of a track. The particles associated with different tracks were classified according to emulsion terminology (21) on the basis of their specific ionization g*(=g/go), where g is the ionization of the track and go is the ionization of the primary. The tracks with g* 10 were named as grey and black tracks respectively. The particles associated with grey and black tracks are also called as slow particles, grey tracks are mostly target protons. In this study two more data sets were used, one at 50 GeV (18) pion-nucleus interactions and the other at 400 GeV (18) proton-nucleus interactions. Thus the analysis is based at three energies i.e., 50, 340 and 400 GeV. Other details may be found in our earlier publications(10,18).