Production of NeutralV-Events by Cosmotron Neutrons

Approximately 2000 cloud chamber pictures have been taken in the forward beam of neutrons produced by high-energy protons striking a beryllium target in the cosmotron. Nine $V$-events interpreted as the decay of a neutral particle produced in a one-inch lead plate in the cloud chamber, were observed. The neutron flux is estimated, from stars observed in the argon gas of the chamber, to be 140 per picture. An upper limit to the cross section for ${\Lambda }^0$-production of 3 millibarns per lead nucleus is deduced for the mesonproducing neutrons.