Measurement of proton-dissociative diffractive photoproduction of vector mesons at large momentum transfer at HERA

Diffractive photoproduction of vector mesons, gammap --> VY, where Y is a proton-dissociative system, has been measured in e(+)p interactions with the ZEUS detector at HERA using an integrated luminosity of 25 pb(-1). The differential cross section, dsigma/dt, is presented for 1.2 < -t < 12 GeV(2), where t is the square of the four-momentum transferred to the vector meson. The data span the range in photon-proton centre-of-mass energy, W, from 80 GeV to 120 GeV. The t distributions are well fit by a power law, dsigma/dt proportional to (-t)(-n). The slope of the effective Pomeron trajectory, measured from the W dependence of the rho(0) and phi cross sections in bins of t, is consistent with zero. The ratios dsigma(gammap-->phiY)/dt to dsigma(gammap-->rho0Y)/dt and dsigma(gammap-->J/psiY)/dt to dsigma(gammap-->rho0Y)/dt increase with increasing -t. Decay- angle analyses for rho(0), phi and J/psi) mesons have been carried out. For the rho(0) and phi mesons, contributions from single and double helicity flip are observed. The results are compared to expectations of theoretical models.