Status of soft photon production in hadronic interactions

A review of experimental results on soft photon production in hadronic collisions is presented. Results from WA27, NA22, HELIOS, WA83, WA91 experiments are discussed. A more detailed presentation of SOPHIE/WA83 and WA91 experimental analysis of data on pi /sup -/p at 280 GeV/c interactions at the CERN OMEGA spectrometer is given. Both experiments show a similar excess of soft photons over the inner hadronic Bremsstrahlung, concentrated mainly, in the energy region 0.2<E gamma <1 GeV and P/sub T/<60 MeV/c. Furthermore, new preliminary results from WA102 experiment studying soft photons produced in pp interactions at 450 GeV/c show the same type of excess. These observations agree with the results of WA27 and NA22 experiments, which have overlapping kinematic regions (Y/sub cms/>0) but not with HELIOS results with photons measured at Y/sub cms/<or =0.0. (15 refs).