Diffractive Photoproduction of Psi(2S) Mesons at HERA

Abstract: Results on diffractive photoproduction of psi(2S) mesons are presented using data collected between 1996 and 2000 with the H1 detector at the HERA ep collider. The data correspond to an integrated luminosity of 77 pb^-1. The energy dependence of the diffractive psi(2S) cross section is found to be similar to or possibly somewhat steeper than that for J/psi mesons. The dependences of the elastic and proton dissociative psi(2S) photoproduction cross sections on the squared momentum transfer t at the proton vertex are measured. The t-dependence of the elastic channel, parametrised as e^bt, yields b_(el)^psi(2S)=(4.31+-0.57+-0.46) GeV^-2, compatible with that of the J/psi. For the proton dissociative channel the result b_(pd)^psi(2S)=(0.59+-0.13+-0.12) GeV^-2 is 2.3 standard deviations smaller than that measured for the J/psi. With proper account of the individual wavefunctions theoretical predictions based on perturbative QCD are found to describe the measurements well.