New Data on elastic J/ψ Production from H1 at HERA

Abstract

New data on cross sections for elastic production of J/ψ mesons in photoproduction and electroproduction are presented for photon virtualities Q2 up to 80 GeV2. The photon‐proton center‐of‐mass energy Wγp covers the ranges 40 ⩽ Wγp ⩽ 305 GeV in photoproduction and 40 ⩽ Wγp ⩽ 160 GeV in electroproduction. The steep rise of the cross sections with Wγp is confirmed. Differential cross sections dσ/dt, where t is the squared four‐momentum transfer at the proton vertex, are measured in the range |t| < 1.2 GeV2 as functions of Wγp and Q2 . An analysis of the J/ψ production and decay angular distributions yields no evidence for a violation of s‐channel helicity conservation. The ratio of the cross sections for longitudinal and transverse photons is measured as a function of Q2 and is found to be described by perturbative QCD models.