The reaction γ d→d ππ , γ p→p ππ and γ n→n ππ were studied in the SLAC 82″ deuterium filled bubble chamber, exposed to a linearly polarized photon beam of 7.5 GeV. All three reactions are dominated by ϱ 0 production. The differential cross section has a slope of ∼6.5 GeV −2 for nucleon reactions and a slope of ∼27 GeV −2 for coherent deuteron reactions. The behaviour of the density matrix elements shows that ϱ production conserves s -channel c.m.s. helicity and is dominated by natural parity exchange.
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We have measured the total and differential cross-sections for coherently photoproduced ϱ, ω and ϱ′ on deuterium at 7.5 GeV. Using VDM relations, we have obtained γ ω 2 / γ ϱ 2 = 7.1 ± 1.5, σ T ( ϱ d) = (54 ± 2) mb and σ T ( ω d) = (56 ± 5) mb. Assuming the amplitude for ϱ′ production via an intermediate ϱ 0 to be small and that the amplitudes for ϱp and ϱ′p elastic scattering are comparable, we found γ ϱ ′ 2 / γ ϱ 2 = 6.0 ± 1.2 and σ T ( ϱ ′d) = (47 ± 6) mb.
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FROM AN EXPONENTIAL FIT WITH DEUTERON FORM FACTOR.
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