Diffractive production of ρ 0 (770) mesons in muon-proton interactions at 470 GeV

The diffractive production of ρ 0 (770 @#@) mesons in muon-proton interactions is studied in the kinematic region 0.15 GeV 2 < Q 2 < 20 GeV 2 and 20 GeV < ? < 420 GeV. The data were obtained in the Fermilab fixed-target experiment E665 with primary muons of 470 GeV energy. Results are presented on the Q 2 , x and ? dependence of the cross section, on the shape of the ρ + ρ t - mass spectrum, on the slope of the diffraction peak and on the production and decay angular distributions of the ρ 0 (770). The cross section for diffractive production of ρ 0 by virtual photons on protons depends mainly on Q 2 . At fixed Q 2 , no significant dependence on x or ? is observed. The extrapolation to Q 2 = 0 yields a photoproduction cross section of (10.30 ± 0.33) μb. The slope of the t′ distribution has a value of (7.0 ± 0.2) GeV −2 , with a tendency to decrease as Q 2 increases. The production and decay angular distributions of the ρ 0 depend strongly on Q 2 and are consistent with s -channel helicity conservation. The ratio R = σ l /σ t deduced from the decay angular distributions rises strongly with Q 2 , passing the value of 1 at Q 2 ≈ 2 GeV 2 .