Resonance production in the reaction γp → p π+π−π+π− in the energy range Eγ = 3.0−18.0 GeV

Abstract

The reaction γp → p π + π − π + π − is studied from the point of view of resonance production. Data from the DESY and SLAC streamer-chamber experiments are combined to permit a consistent analysis over the energy range of E γ = 3−18 GeV. Cross sections, invariant-mass, momentum-transfer, and other experimental distributions are given. A maximum-likelihood fit is performed to give quantitative results on the production cross section of the identifiable resonance channels present. In addition to the usual invariant-mass and momentum-transfer plots, diagrams suggested by theLPS and inclusive descriptions are used to test the quality of the fits and to emphasize aspects of this reaction. A combination of non-interfering peripheral resonance-production channels is found to describe adequately the reaction in all E γ intervals studied. In particular, it is found that ϱ′(∼1500 MeV) production is required by the data. Other resonance-production channels important over this energy range are γp → p ϱ O π + π − and γp → Δ ++ π − ϱ O . Evidence for γp → Δ ++A 1 − and γp → Δ ++A 2 − is found only for E γ ⩽ 6.5 GeV. Part of the Δ ++ production may be explained by the cascade decay N ∗ → Δ ++π − .