Volume 62B, number 2 PHYSICS LETTERS 24 May 1976 COMPARISON OF NEUTRAL PARTICLE PRODUCTION IN 100 GeV/c ~p AND pp INTERACTIONS D.R. WARD, R.E. ANSORGE, C.P. BUST, J.R. CARTER, W.W. NEALE and J.G. RUSHBROOKE Cavendish Laboratory 1, Cambridge, England C. MOORE, R. RAJA, L. VOYVODIC and R.J. WALKER Fermi National Accelerator Laboratory 2, Batavia, Ill. 60510, USA W. MORRIS a , B.Y. OH, D.L. PARKER 4 , G.A. SMITH and J. WHITMORE Michigan State University ~:, E. Lansing, Michigan 48824, USA Received 12 April 1976 We derive cross-sections for the inclusive production in i~P interactions at 100 GeV/c of ~r ° , K° and A0fA ° of 91.5-+5.7 mb, 5.2-+0.4mb and 4.8-+0.4 mb respectively, which are all higher than pp cross-sections at this energy. We find indications that these differences can be attributed to "annihilation" processes. Introduction. We present results on the production of 3', Ks °, A ° and ~o in ~p interactions at 100 GeV/c. We also look for differences between pp and ~p inter- actions, which could be ascribed to the effects of "an- nihilation" processes. Both the present experiment and pp experiments at this energy suffer from limited sta- tistics, but we find that cross-sections for the produc- tion of neutral particles are in all cases somewhat higher in ~p interactions than in pp interactions. In the case of A °/~o production (and possibly 3"s) the difference appears to arise mainly in the neighbour- hood of y* = 0, characteristic of a central production process. The data to be described are the first on ~p ~ neu- trals above 14.75 GeV/c, and come from a 100 000 picture exposure of the 30" hydrogen bubble chamber at Fermilab to a tagged beam of negative particles. Information on the ~p charged multiplicity distribution 1 Work supported by the Science Research Council, UK. 2 Operated by the Universities Research Association, Inc., under Contract with the Energy Research and Development Administration, USA. 3 Presently at General Atomic Company, San Diego, CA 92138, USA. 4 Presently at Department of Physics, Iowa State University, Ames, Iowa, 50010, USA. s Work supported in part by the National Science Foundation, USA. at 100 GeV/c [1 j and on the difference between ~p and pp topological cross-sections [21 has already been published. The efficiency for scanning for V°'s was about 90% for singly scanned film, and after measure- ment and remeasurement 93% of events had been satis- factorily measured. After all cuts we have 1015 V O,s associated to events inside our fiducial volume giving fits to A ° , K s and ,~o decays, or 3' ~ e+e - conversion. Ambiguities (affecting about 9% of the events) were resolved by observing ionizations where possible, and otherwise by cuts on the transverse momentum of the decays and on the ×2 probabilities of the fits. The data were corrected for scanning and measuring losses, for losses of V °'s decaying or converting outside the fiducial volume, or closer than 3 cm (2 cm in the case of Ks °) to the production vertex, and for inter- actions of the strange particles. The pair production cross-section was taken from ref. [3], and the strange particle cross-sections were corrected for branching ratios taken from ref. [4]. A correction (~ 2-3%) was made for the loss of 3"s below 40 MeV/c using the sym- metry of the reaction ~p ~ 3' in the c.m. system. Cross-sections and multiplicities. In table 1 we give cross-sections for A°/.A °, K ° and rr ° production, the latter taken to be ½ o(~p ~ 3'). We have used events in both forward and backward hemispheres in the c.m. system for the 3"s, since, apart from the loss of very slow 3"s, no forward/backward asynlmetry was found 237