Diffractive photoproduction of ψ(2 S) mesons at HERA

Abstract

Results on diffractive photoproduction of ψ(2 S) 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 ψ(2 S) cross section is found to be similar to or possibly somewhat steeper than that for J/ ψ mesons. The dependences of the elastic and proton dissociative ψ(2 S) 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 ψ(2 S) =(4.31±0.57±0.46) GeV −2, compatible with that of the J/ ψ. For the proton dissociative channel the result b pd ψ(2 S) =(0.59±0.13±0.12) GeV −2 is 2.3 standard deviations smaller than that measured for the J/ ψ. With proper account of the individual wavefunctions theoretical predictions based on perturbative QCD are found to describe the measurements well.