PHYSICAL RKVIK% C VOLUME 23, NUMBER 4 APRIL 1981 Inclusive scattering of protons on helium, nickel, and tantalum at 500 Mev G. Roy, L G. Greeniaus, G. A. Moss, D. A. Hutcheon, and R. I iljestrand Uniuersity ofAlberta, Edmonton, Alberta, Canada T66 2N5 R. M. %'oloshyn TRIUMF, Vancouuer, British Columbia, Canada V6T2A3 D. H. Boal Simon Fraser Uniuersity, Burnaby, British Columbia, Canada VSA IS6 A. %. Stetz Uni uersity of Oregon, Coruallis, Oregon 97331 K. Aniol Uniuernty of washington, Seattle, washington 98195 A. Willis and N. %illis Institut de Physique Nucleaire, I406 Orsay, France R. McCamis Uniuersity of Manitoba, 8'innipeg, Manitoba, Canada R3T 2N2 CReceived 26 August 1980I %'e have performed proton inclusive scattering measurements at 500 MeV on 'He, Ni, and Ta at angles at 65', 90, 120', and 160'. Analyzing powers were also obtained for 'He and Ni. The data extend in energy to the elastic scattering peak for 'He at 90'. The cross-section data are described well by a direct knockout model and by quasi- two-body scaling calculations. Fits to analyzing power results by these theories are poor, and furthermore, we find a qualitative difference between the 'He and Ni results. The Ni data show large positive analyzing powers at high detected particle energies, in keeping with results obtained on various targets from 'I. i to '"Ta at 800 MeV bombarding energy; the 'He analyzing powers are predominantly negative or close to zero. NUCLEAR REACTIONS Proton inclusive scattering; 4He, Ni, I I'a; E= 500 Mev; measured e(EJ, P(EJ. I. INTRODUCTION Much interest has been shown recently in large angle proton induced inclusive scattering' ' (i. e. , p+A- p+anything} at medium and high energies. Protons observed at laboratory angles greater than 90 are in a region kinematically forbidden for free nucleon-nucleon scattering, so the fact that the target is a nucleus plays an essential role. This has been taken into account in a variety of models with different reaction mechanisms. These models include evaporation, ' intranuclear cascade with pion production and absorption, ' scattering from clusters in the target, ' multinucleon ex- change, and scattering from a bound nucleon of high momentum. " All of these models can be eonstrueted to work equally well over a limited range of energy and angle. To test them fully, data are needed over the widest possible range of energy. In this paper we present some new re- sults for 500 MeV proton inclusive scattering ob- tained at the TRIUMF cyclotron. Cross sections are reported for helium, nickel, and tantalum targets. These are the first results fox large angle inclusive proton production on a target as light as helium. Previous experiments on large angle inclusive proton production have been done at incident en- ergies of 600 MeV and higher with the most com- plete measurements at 800 MeV. " Our motivation for extending the energy down to 500 MeV is two- fold. First, the cross section for pion production in nucleon-nucleon collisions changes dramatically in the 500-800 MeV range. If real pion production and absorption is a dominant mechanism for large angle proton emission, ' we would expect to see large qualitative changes in inclusive cross sec- tions over this energy range. Second, at 800 MeV, whexe the most complete measurements have been made, a scaling behavior" (quasi-two-body scaling) has been observed. This scaling follows as an approximation to a direct knockout mecha- 1981 The Amencan Phys&cal Society