We have searched for direct photons of low $P_T$ (≤1.0 GeV/c) at ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}=90\mathrm{}\mathrm{°}}$ in pp collisions at √s =63 GeV. We used two independent methods: direct detection in NaI crystals and conversion to $e^{+}$$e^{\mathrm{-}}$ pairs. No signal is observed; the photon spectrum is well described by the decay of hadrons. The result is consistent with a direct low-$P_T$ photon signal reported at √s =12 GeV, but excludes a rapid growth of soft-photon production with √s .

• Received 13 April 1987

DOI:https://doi.org/10.1103/PhysRevD.36.2615