A measurement of the t dependence of the helicity structure of diffractive ρ meson electroproduction at HERA

Abstract

The helicity structure of the diffractive electroproduction of ρ mesons, e+ p→ e+ ρ+ Y, is studied in a previously unexplored region of large four-momentum transfer squared at the proton vertex, t: 0< t′<3 GeV 2, where t′=| t|−| t| min. The data used are collected with the H1 detector at HERA in the kinematic domain 2.5< Q 2<60 GeV 2, 40< W<120 GeV. No t dependence of the r 04 00 spin density matrix element is found. A significant t dependent helicity non-conservation from the virtual photon to the ρ meson is observed for the spin density matrix element combinations r 5 00+2 r 5 11 and r 1 00+2 r 1 11. These t dependences are consistently described by a perturbative QCD model based on the exchange of two gluons.