Measurements of inelastic J / psi and psi-prime photoproduction at HERA

The cross sections for inelastic photoproduction of J/psi and psi' mesons have been measured in ep collisions with the ZEUS detector at HERA, using an integrated luminosity of 38.0 pb-1. The events were required to have 0.1 < z < 0.9 and 50 < W < 180 GeV, where z is the fraction of the incident photon energy carried by the J/psi in the proton rest frame and W is the photon-proton centre-of-mass energy. The psi' to J/psi cross-section ratio was measured in the range 0.55 < z < 0.9. The J/psi data, for various ranges of transverse momentum, are compared to theoretical models incorporating colour-singlet and colour-octet matrix elements. Predictions of a next-to-leading-order colour-singlet model give a good description of the data, although there is a large normalisation uncertainty. The J/psi helicity distribution for z > 0.4 is compared to leading-order QCD predictions.Comment: 31 pages, 10 figure

Measurement of the photon-proton total cross section at a center-of-mass energy of 209 GeV at HERA

The photon-proton total cross section has been measured in the process e/sup +/p to e/sup +/ gamma p to e/sup +/X with the ZEUS detector at HERA. Events were collected with photon virtuality Q/sup 2/ lt 0.02 GeV/sup 2/ and average gamma p center-of-mass energy W/sub gamma p/=209 GeV in a dedicated run, designed to control systematic effects, with an integrated luminosity of 49 nb/sup -1/. The measured total cross section is sigma /sub tot//sup gamma p/ = 174+or-1 (stat.)+or-13 (syst.) mu b. The energy dependence of the cross section is compatible with parameterizations of high-energy pp and pp data

Measurement of the Q and energy dependence of diffractive interactions at HERA

Diffractive dissociation of virtual photons, gamma*p --> Xp, has beer, studied ill ep interactions with the ZEUS detector at HERA. The data cover photon virtualities 0.17 3 GeV2. The ratio of the diffractive to the virtual photon-proton total cross sect ion is studied as a function of W and Q(2). Comparisons are made with a model based oil perturbative QCD

Measurement of high Q**2 e- p neutral current cross-sections at HERA and the extraction of xF(3)

Cross sections for e(-)p neutral current deep inelastic scattering have been measured at a centre-of-mass energy of 318 GeV using an integrated luminosity of 15.9 pb(-1) collected with the ZEUS detector at HERA. Results on the double- differential cross-section d(2)sigma/dx dQ(2) in the range 185 lt Q(2) lt 50 000 GeV2 and 0.0037 lt x lt 0.75, as well as the single-differential cross-sections dsigma/dQ(2), dsigma/dx and dsigma/dy for Q(2) gt 200 GeV2, are presented. To study the effect of Z-boson exchange, dsigma/dx has also been measured for Q(2) gt 10 000 GeV2. The structure function xF(3) has been extracted by combining the e(-)p results presented here with the recent ZEUS measurements of e(+)p neutral current deep inelastic scattering. All results agree well with the predictions of the Standard Model