Elastic scattering of target protons in nucleon-nucleus collisions

Abstract

The study of elastic nucleon-nucleon collisions in the energy region above 100 GeV is of special interest in respect of 1) the primary-energy dependence of the total elastic cross-section and 2) the increase of interaction radius of a nucleon with increasing primary energy, which have been conjectured by the extensive studies in the energy region below 30 GeV. At present, since cosmic rays are the only source for high-energy particles (> 100 GeV), the problem is not explored as has been done at accelerator energy. The elastic scatterings of high-energy cosmic-ray particles by free protons or protons in a target nucleus which give rise to only one visible grey or black track (iV h : 1) in nuclear emulsion are very rare and it is difficult to find them. Only a few such experiments have so far been carried out (1.s). There is, however, a probability in an inelastic nucleon-nucleus collision that an incident pr imary nucleon, during the collision with nucleus, collides elastically with other nucleons in the same nucleus producing (( knock-on protons ~ which appear as grey tracks ((30--500) MeV) in nuclear emulsion. The frequency of these elastic p-p collisions in nuclei depends on I) the total elastic p-p cross-section and II) the interaction radius of the nucleon. A rough estimate shows that these elastic protons are expected to be ~ 0.5 per proton-light-nucleus (Z = 7) collision if a 5 mb total elastic cross-section when 1 fm interaction radius is assumed. Therefore, the problems I) and II) mentioned above can be investigated by using knock-on protons associated with inelastic nucleonnucleon interactions. A sample of 67 nucleon-light-nucleus interactions with ZTh~ 7 and primary energy between 50 and 10 a GeV found in the Dublin part of the ICEF stack has been analysed. The grain density, multiple scattering and in some cases the range were measured for all grey tracks whose dip angles to emulsion surface were ~ 30 ~ Also the energy and the polar angle to the direction of the primary of those tracks have been determined. We identified 41 knock-on protons with kinetic energy greater than 30 5[eV. The analysis for nucleon-nucleus events is based on this sample and is shown in Table I. The number of knock-on protons Pk observed, with dip angle ~ 30 ~ is given in the 4th and 5th line of Table I for E(pk)~ 30 MeV.