Bubble-Chamber Study of Photoproduction by 2.8- and 4.7-GeV Polarized Photons. I. Cross-Section Determinations and Production ofρ0andΔ+<…

Photoproduction is studied at 2.8 and 4.7 GeV using a linearly polarized monoenergetic photon beam in a hydrogen bubble chamber. We discuss the experimental procedure, the determination of channel cross sections, and the analysis of the channel yp p~‘n-. A model independent analysis of the p” decay angular distribution allows us to measure nine independent density matrix ‘elements. From these we find that the reaction yp--pp” proceeds almost completely through natural parity exchange for momentum transfers It I < 1 GeV2 and that the rho production mechanism is consistent with s-channel c.m. s. helicity conservation for It I < 0.4 GeV2. A cross section for the production of n.‘npairs in the s-channel c. m. s. helicity-conserving p-wave state is determined. The rho mass shape is studied as a function of momentum transfer and is found to be inconsistent with a t-independent Ross-Stodolsky factor. Using a t-dependent parameterization of the p” mass shape we derive a phenomenological p” cross section. We compare our phenomenological p” cross section with other experiments and find good agreement for 0.05 < It I < 1 GeV2. We discuss the discrepancies in the various determinations of the forward differential cross section. We study models for p” photoproduction and find that the Soding model best describes the data. Using the Sijding model we determine a p” cross section. We determine cross sections and nine density matrix elements for yp -c a*~-. The parity asymmetry for A++ production is incompatible with simple one pion exchange. We compare A ‘$production with models.