Observation of direct soft photon production in π−p interactions at 280 GeV/ c

Abstract

The OMEGA spectrometer, equipped with a hydrogen target and two electromagnetic calorimeters, was used to investigate the production of soft gammas in hadronic collisions. The E γ and P T distributions of the measured γ's are compared with the corresponding distributions of γ's arising from hadronic decays and of γ's expected from QED inner bremsstrahlung. An excess of gammas by a factor of 7.9 ± 1.4 over the QED prediction is measured in the low energy (0.2< E γ <1.0 GeV) and low P T (< 10 MeV/ c) kinematic region, and confirms the original observation of a similar effect in a bubble chamber experiment.