2000/10/31 by J. A. Crittenden
Physics and Astronomy · #hep-ex
published as Int.J.Mod.Phys. A16S1A (2001) 187-190 · Contributed to the proceedings of DPF2000, the meeting of the Division of Particles and Fields of the American Physical Society, August 9-12, 2000, Columbus, Ohio, USA (3 pages including 2 figures) Replaced to remove postscript format error. Transparencies are available at http://www-zeus.physik.uni-bonn.de/~critten/dpf2000/dpft/index.html
We discuss recent preliminary results on the diffractive photoproduction of \rhoz, ϕ, and \jpsi mesons at high momentum transfer reported by the ZEUS collaboration at HERA. A special-purpose calorimeter served to tag the quasi-real photons (\qsq<0.01 \gevsq) in the process γ+ p → \rm VM+ Y, where Y represents a dissociated state of the proton. The resulting range in photon-proton center-of-mass energy extends from 80 to 120 \gev. The differential cross sections (\Dσ)/(\D t) were obtained in the region \abst>1.2 \gevsq, where t denotes the squared momentum transfer to the proton. The measurements provide good sensitivity to the observed power-law dependence (\Dσ)/(\D t) ∝ (-t)-n. Over the region in momentum transfer covered by the data, the power is found to be approximately n≃ 3 for \rhoz and ϕ photoproduction, and approximately n≃ 2 for \jpsi photoproduction.