Reactions γp → π+π-π+π-p and γp → K/sup +/-/π/sup -/+/K0p at 20 GeV

The reactions γp → π+π-π+π-p and γp → K/sup +/-/π/sup -/+/K0p at 20 GeV are studied from data obtained during the BC72 experiment, run at the SLAC 1 meter Hybrid Bubble Chamber facility from 1980 to 1982. The 5702 events in the first channel represent a cross section of 2.54 +/- 0.24 μb; the 235 events in the second channel represent a cross section of 380 +/- 40 nb. The primary radial excitation of the rho(770), commonly called the rho(1600), is observed in half of the 4π channel, but with parameters markedly different from what has been previously published. Production of the resonance is peripheral, exponential t dependence 0f 7.5 (GeV)-2, with s-channel helicity conserved at the 90% level. A variety of methods have been used to calculate the mass and the width of the rho' resonance, the strongest (and new for this channel) being a maximum likelihood fit to all aspects of the 4π data. Forty percent of the 4π channel is associated with Δ++ (1232) production. The author has studied, in particular, γp → A/sub n/Δ++ and see predominantly production of the A2 tensor meson resonance with an admixture of the pseudoscalar A1 mean resonance. The KKπ channel is dominated by K/sup */K system does not appear to be associated with resonance production