Measurement of (Anti)deuteron and (Anti)proton Production in DIS at HERA

The first observation of (anti)deuterons in deep inelastic scattering at HERA has been made with the ZEUS detector at a centre-of-mass energy of 300-318 GeV using an integrated luminosity of 120 pb-1. The measurement was performed in the central rapidity region for transverse momentum per unit of mass in the range 0.3 \u3c pT / M \u3c 0.7. The particle rates have been extracted and interpreted in terms of the coalescence model. The (anti)deuteron production yield is smaller than the (anti)proton yield by approximately three orders of magnitude, consistent with the world measurements. © 2007 Elsevier B.V. All rights reserved

High-E_T dijet photoproduction at HERA

The cross section for high-E_T dijet production in photoproduction has been measured with the ZEUS detector at HERA using an integrated luminosity of 81.8 pb-1. The events were required to have a virtuality of the incoming photon, Q^2, of less than 1 GeV^2 and a photon-proton centre-of-mass energy in the range 142 < W < 293 GeV. Events were selected if at least two jets satisfied the transverse-energy requirements of E_T(jet1) > 20 GeV and E_T(jet2) > 15 GeV and pseudorapidity requirements of -1 < eta(jet1,2) < 3, with at least one of the jets satisfying -1 < eta(jet) < 2.5. The measurements show sensitivity to the parton distributions in the photon and proton and effects beyond next-to-leading order in QCD. Hence these data can be used to constrain further the parton densities in the proton and photon.Comment: 36 pages, 13 figures, 20 tables, including minor revisions from referees. Accepted by Phys. Rev.

High-ET Dijet Photoproduction at HERA

The cross section for high-ET dijet production in photoproduction has been measured with the ZEUS detector at HERA using an integrated luminosity of 81.8pb-1. The events were required to have a virtuality of the incoming photon, Q2, of less than 1GeV2 and a photon-proton center-of-mass energy in the range 14215GeV and pseudorapidity (with respect to the proton beam direction) requirements of -1\u3cηjet1,

Measurement of J/ψ Helicity Distributions in Inelastic Photoproduction at HERA

The J/ψ decay angular distributions have been measured in inelastic photo-production in ep collisions with the ZEUS detector at HERA, using an integrated luminosity of 468 pb-1. The range in photon-proton centre-of-mass energy, W, was 50 \u3c W \u3c 180 GeV. The J/ψ mesons were identified through their decay into muon pairs. The polar and azimuthal angles of the μ+ were measured in the J/ψ rest frame and compared to theoretical predictions at leading and next-to-leading order in QCD. © SISSA 2009

Production of Excited Charm and Charm-Strange Mesons at HERA

The production of excited charm, D 1(2420)0 and D 2* (2460)0, and charm-strange, D s1(2536)±, mesons in ep collisions was measured with the ZEUS detector at HERA using an integrated luminosity of 126 pb -1. Masses, widths and helicity parameters were determined. The measured yields were converted to the rates of c quarks hadronising as a given excited charm meson and to the ratios of the dominant D 2* (2460)0 and D s1(2536) ± branching fractions. A search for the radially excited charm meson, D *(2640)±, was also performed. The results are compared with those measured previously and with theoretical expectations. © 2009 Springer-Verlag / Società Italiana di Fisica

Diffractive Photoproduction of Dijets in ep Collisions at HERA

Diffractive photoproduction of dijets was measured with the ZEUS detector at the ep collider HERA using an integrated luminosity of 77.2 pb-1. The measurements were made in the kinematic range Q2 \u3c 1 GeV 2, 0.2

Measurement of D Mesons Production in Deep Inelastic Scattering at HERA

Charm production in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 82 pb-1. Charm has been tagged by reconstructing D*+, D0, D+ and D+s (+ c.c.) charm mesons. The charm hadrons were measured in the kinematic range pT (D* +,D 0,D+) \u3e 3GeV, pT (D+s ) \u3e 2GeV and |η(D)| \u3c 1.6 for 1.5 \u3c Q2 \u3c 1000GeV2 and 0.02 \u3c y \u3c 0.7. The production cross sections were used to extract charm fragmentation ratios and the fraction of c quarks hadronising into a particular charm meson in the kinematic range considered. The cross sections were compared to the predictions of next-to-leading-order QCD, and extrapolated to the full kinematic region in pT (D) and η(D) in order to determine the open-charm contribution, Fcc2 (x,Q2), to the proton structure function F2. © SISSA 2007

Forward-Jet Production in Deep Inelastic ep Scattering at HERA

Forward jet cross sections have been measured in neutral current deep inelastic scattering at low Bjorken-x with the ZEUS detector at HERA using an integrated luminosity of 81.8 pb-1. Measurements are presented for inclusive forward jets as well as for forward jets accompanied by a dijet system. The explored phase space, with jet pseudorapidity up to 4.3 is expected to be particularly sensitive to the dynamics of QCD parton evolution at low x. The measurements are compared to fixed-order QCD calculations and to leading-order parton-shower Monte Carlo models. © 2007 Springer-Verlag / Società Italiana di Fisica

Bose-Einstein Correlations of Charged and Neutral Kaons in Deep Inelastic Scattering at HERA

Bose-Einstein correlations of charged and neutral kaons have been measured in e ± p deep inelastic scattering with an integrated luminosity of 121 pb -1 using the ZEUS detector at HERA. The two-particle correlation function was studied as a function of the four-momentum difference of the kaon pairs, Q 12 = sqrt(- (p 1 - p 2) 2), assuming a Gaussian shape for the particle source. The values of the radius of the production volume, r, and of the correlation strength, λ, were obtained for both neutral and charged kaons. The radii for charged and neutral kaons are similar and are consistent with those obtained at LEP. © 2007 Elsevier B.V. All rights reserved