Comparison of photon and hadron induced production of ρ⁰ mesons in the energy range of 65 to 175 GeV

Abstract

The inclusive production of ρ⁰ mesons was measured in γp andh ^± p collisions at beam energies of 65 GeV≦E _γ≦175 GeV andE _h =80, 140 GeV, respectively, whereh is π orK. Cross sections were determined for all beams and energies as functions ofx _F (−0.1≦x _F≦1.0),p _T (0≦p _T≦3.5 GeV/c) and the polar decay angle of the ρ⁰ by fitting the ρ⁰ signal in π⁺π^- mass distributions. The ρ⁰ line shape is found to be distorted from a pure Breit-Wigner distribution throughout most of thex _F−p _T plane for both photon and hadron beams and a simple explanation is suggested. Throughout the paper emphasis is put on the comparison of photon and hadron beam data. The comparison of cross sections of γp andhp data provides a measure of the Vector Meson Dominance factor throughout thex _F−p _T range of the ρ⁰. The ρ⁰ production at lowp _T can be described for both photon and hadron beams by a triple regge model at largex _F. Similarly central production is well described by the quark-antiquark fusion model. At largep _T there is an excess of ρ⁰ photoproduction which is consistent with the expected onset of pointlike photon interactions.