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Comment: 4 pages, 3 figures (eps), fully revised version, to be published in PRB (Brief Reports)
The e(+)p neutral-current deep inelastic scattering differential cross-sections d sigma/dQ(2), for Q(2) gt 400 GeV2, d sigma/dx and d sigma/dy, for Q(2) gt 400, 2500 and 10000 GeV2, have been measured with the ZEUS detector at HERA. The data sample of 47.7 pb(-1) was collected at a center-of-mass energy of 300 GeV. The cross-section, d sigma/dQ(2), falls by six orders of magnitude between Q(2) = 400 and 40000 GeV2. The predictions of the Standard Model are in very good agreement with the data. Complementing the observations of time-like Z(0) contributions to fermion-antifermion annihilation! the data provide direct evidence for the presence of Z(0) exchange in the space-like region explored by deep inelastic scattering.
Diffractive production of D*+/-(2010) mesons in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 44.3 pb(-1). Diffractive charm production is identified by the presence of a large rapidity gap in the final state of events in which a D*+/- (2010) meson is reconstructed in the decay channel D*+/- → (D-0 → K(-)pi(+))pi(s)(+) (+ charge conjugate). Differential cross sections when compared with theoretical predictions indicate the importance of gluons in such diffractive interactions.
Inclusive event-shape variables have been measured in the current region of the Breit frame for neutral current deep inelastic ep scattering using an integrated luminosity of 45.0 pb/sup -1/ collected with the ZEUS detector at HERA. The variables studied included thrust, jet broadening and invariant jet mass. The kinematic range covered was 10 lt Q/sup 2/ lt 20 480 GeV/sup 2/ and 6 * 10/sup -4/ lt * lt 0.6, where Q/sup 2/ is the virtuality of the exchanged boson and x is the Bjorken variable. The Q dependence of the shape variables has been used in conjunction with NLO perturbative calculations and the Dokshitzer-Webber non-perturbative corrections ('power corrections') to investigate the validity of this approach.
The exclusive photoproduction of J/psi mesons, gammap → J/psip, has been studied in ep collisions with the ZEUS detector at HERA, in the kinematic range 20 lt W lt 290 GeV, where W is the photon-proton centre-of-mass energy. The J/psi mesons were reconstructed in the union and the electron decay channels using integrated luminosities of 38 pb(-1) and 55 pb(- 1), respectively. The helicity structure of J/psi production shows that the hypothesis of s-channel helicity conservation is satisfied within two standard deviations. The total cross section and the differential cross-section dsigma/dt, where t is the squared four-momentum transfer at the proton vertex, are presented as a function of W, for \t\ lt 1.8 GeV2. The t distribution exhibits an exponential shape with a slope parameter increasing logarithmically with W with a value b...
Events with a final-state proton carrying a large fraction of the proton beam momentum, x(L) gt 0.6, and the square of the transverse momentum p(T)(2) lt 0.5 GeV2 T, have been studied in e(+)p collisions with the ZEUS detector at HERA. Data with different photon virtualities were used: Q(2) lt 0.02 GeV2, 0.1 lt Q(2) lt 0.74 GeV2 and 3 lt Q(2) lt 254 GeV2, corresponding to integrated luminosities of 0.9, 1.85 and 3.38 pb(-1). The cross sections are given as a function of x(L), p(T)(2), Q(2) and the Bjorken scaling variable, x. The ratio of the cross section for leading proton production to the inclusive e(+)p cross section shows only a mild dependence on Q(2) and on x. In the region 0.6 lt x(L) lt 0.97, the relative yield of protons is only a weak function of x(L).
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