出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：Recent results from the H1 and ZEUS experiments are reviewed. The cross sections of elastic
photo- and electroproduction of the vector mesons f and J/y are measured as functions of Q2,W
and t. The large statistics and the large coverage in t and W allow the determination of the
effective Regge exchange trajectories, which are found to be different from the soft pomeron
trajectory. Shrinkage is observed in the J/y photoproduction.
Helicity analyses are used to determine the spin density matrix element r04
00 and the Q2 dependence
of the ratio of the cross sections for longitudinally and transversely polarised photons. S-channel
helicity conservation (SCHC) is confirmed for J/y production
While the properties of the f production put it in a position between “soft” and “hard” diffraction,
the J/y production shows “hard” features already in photoproduction. All observed properties are
consistent with the view of the production process as a photon induced q ¯ q pair scattering off the
proton, thereby forming a vector meson. pQCD-based models are able to give a fair description
of the data when at least one of the involved scales reaches a large value. The J/y data show some
sensitivity to the parameterisation of the gluon distribution in the proton.
Finally, an analysis of Deep Virtual Compton Scattering is reported. The t dependence of the cross
section is measured for the first time. Measurements of the W and Q2 dependences of the DVCS
cross section are also presented. A pQCD-based model with calculations in next-to-leading order
describes the data rather well.
