Production of vector mesons by muons in a hybrid bubble-chamber experiment

We present results on vector-meson leptoproduction in the SLAC fast-cycling 40-in. hydrogen bubble chamber exposed to 16-GeV/c muons. From 3644 inelastic events we obtained 495 events of μ⁻p->μ⁻π⁺π⁻p, of which approximately 160 are ρ events with W>2 GeV and Q²>0.05 GeV². Analyzing these data in the same way as in our previous photoproduction experiment, we find the ρ⁰ contribution to σtₒt decreases by about 35% between Q²=0 and 1 GeV², and the exponential slope parameter becomes approximately 20% smaller, although within errors it is still consistent with the photoproduction value. The decay angular distribution of the ρ⁰ shows a substantial cos²θ component which can be interpreted as evidence for production by longitudinal photons assuming s-channel helicity is conserved. Data from 39 ω-production events are also presented. Upper limits for φ and ρ^' production are given.