Study of the reaction γp → rho- Δ++ at 20 GeV

A clean sample of γp → rho- Δ++ events has been isolated in a hydrogen bubble chamber experiment having a sensitivity of 2.4 events/nb. The experiment uses a narrow band, 20 GeV photon beam produced by backscattering laser light from the Stanford Linear Accelerator's electron beam. A large lead-glass photon detector was used to measure π0's from the rho- → π-π0 decays. We study the s and t dependence of the γp → rho- Δ++ production process and the spin density matrix elements for the decay of the Δ++. These data show that this reaction is not mediated by pure one pion exchange. This result brings in doubt previous measurements of the rho → πγ decay width which use a one pion exchange analysis of the γp → rho- Δ++ reaction. 14 references