Neutral charm production in 400 GeV proton-emulsion interactions

A search has been carried out for neutral charm production in 5,108 proton-emulsion interactions at 400 GeV/c. Nine charm candidates have been observed in our fiducial volume which extends from 100µm-1,000µm in the forward cone. One of these is a 4-prong and the others are 2-prong events with opening angle>10 mrad and momenta of both decay tracks>150 MeV/c. Search for associated charm decays was made in an extended fiducial volume around the primary stars of these nine candidates. This yielded two neutral 2-prong events, one associated with the 4-prong and the other with a 2-prong candidate. All unassociated candidates are consistent with being backgrounds due to K s , Λ decays, neutral interactions and γ conversions whereas the background to associated events is negligible. Based on the two associated decays the inclusive cross section for D 0, -0 production is determined as 27±20 µb/nucleon. Detailed measurements on the 4-prong candidate lead to the identification of one decay track as an electron and another as a kaon. This is interpreted as a semi-leptonic, Cabbibo favoured D 0/D -0 decay