Low transverse momentum photon production in proton-nucleus collisions at 18 GeV/<i>c</i>

Inclusive single photon spectra have been measured in the transverse momentum (${\mathit{p}}_{\mathit{T}}$) range from a few MeV/c up to approximately 1 GeV/c at various nucleon-nucleon center of momentum rapidities (${\mathit{y}}_{\mathit{NN}}$) in the interval from -2.4${\mathit{y}}_{\mathit{NN}}$+0.5 in 18 GeV/c p-Be and p-W collisions. These distributions were used to estimate the inclusive ${\mathit{p}}_{\mathit{T}}$ and rapidity distributions for ${\mathrm{\ensuremath{\pi}}}^{0}$ production over approximately the same kinematic range. The measured photon spectra are compared with the expected distribution of photons from ${\mathrm{\ensuremath{\pi}}}^{0}$ decays and hadronic bremsstrahlung in order to search for new sources of ``soft'' photons at low transverse momentum. The results indicate no anomalous sources of soft photons in either p-Be or p-W interactions at these energies. The p-W data at forward angles set a limit on any excess of low ${\mathit{p}}_{\mathit{T}}$ photons at 2.65 times hadronic bremsstrahlung at the 99% C.L. \textcopyright{} 1996 The American Physical Society.