Measurement of D+- and D0 production in deep inelastic scattering using a lifetime tag at HERA

The production of D-+/-- and D-0-mesons has been measured with the ZEUS detector at HERA using an integrated luminosity of 133.6 pb(-1). The measurements cover the kinematic range 5 < Q(2) < 1000 GeV2, 0.02 < y < 0.7, 1.5 < p(T)(D) < 15 GeV and |eta(D)| < 1.6. Combinatorial background to the D-meson signals is reduced by using the ZEUS microvertex detector to reconstruct displaced secondary vertices. Production cross sections are compared with the predictions of next-to-leading-order QCD, which is found to describe the data well. Measurements are extrapolated to the full kinematic phase space in order to obtain the open-charm contribution, F-2(c (c) over bar), to the proton structure function, F-2

Search for contact interaction, large extra dimensions and finite quark radius in ep collisions at HERA

A search for physics beyond the Standard Model has been performed with high-Q2 neutral current deep inelastic scattering events recorded with the ZEUS detector at HERA. Two data sets, e+p→e +X and e-p→e-X, with respective integrated luminosities of 112 pb-1 and 16 pb-1, were analyzed. The data reach Q2 values as high as 40000 GeV2. No significant deviations from Standard Model predictions were observed. Limits were derived on the effective mass scale in eeqq contact interactions, the ratio of leptoquark mass to the Yukawa coupling for heavy leptoquark models and the mass scale parameter in models with large extra dimensions. The limit on the quark charge radius, in the classical form factor approximation, is 0.85×10 -16 cm. © 2004 Published by Elsevier B.V

STUDY OF DEEP INELASTIC INCLUSIVE AND DIFFRACTIVE SCATTERING WITH THE ZEUS FORWARD PLUG CALORIMETER

Deep inelastic scattering and its diffractive component, ep→e′γ∗p→e′XNep→e′γ∗p→e′XN, have been studied at HERA with the ZEUS detector using an integrated luminosity of 4.2 pb−14.2 pb−1. The measurement covers a wide range in the γ∗pγ∗p c.m. energy W (37–245 GeV), photon virtuality Q 2 (2.2–80 GeV2) and mass MXMX (0.28–35 GeV). The diffractive cross section for MX>2 GeVMX>2 GeV rises strongly with W ; the rise is steeper with increasing Q 2. The latter observation excludes the description of diffractive deep inelastic scattering in terms of the exchange of a single pomeron. The ratio of diffractive to total cross section is constant as a function of W , in contradiction to the expectation of Regge phenomenology combined with a naive extension of the optical theorem to γ∗pγ∗p scattering. Above MXMX of 8 GeV, the ratio is flat with Q 2, indicating a leading-twist behaviour of the diffractive cross section. The data are also presented in terms of the diffractive structure function, View the MathML sourceF2D(3)(β,xP,Q2), of the proton. For fixed β , the Q 2 dependence of View the MathML sourcexPF2D(3) changes with xPxP in violation of Regge factorisation. For fixed xPxP, View the MathML sourcexPF2D(3) rises as β→0β→0, the rise accelerating with increasing Q2. These positive scaling violations suggest substantial contributions of perturbative effects in the diffractive DIS cross section

SUBSTRUCTURE DEPENDENCE OF JET CROSS SECTIONS AT HERA AND DETERMINATION OF ALPHA(S).

Jet substructure and differential cross sections for jets produced in the photoproduction and deep inelastic ep scattering regimes have been measured with the ZEUS detector at HERA using an integrated luminosity of 82.2 pb−182.2 pb−1. The substructure of jets has been studied in terms of the jet shape and subjet multiplicity for jets with transverse energies View the MathML sourceETjet>17 GeV. The data are well described by the QCD calculations. The jet shape and subjet multiplicity are used to tag gluon- and quark-initiated jets. Jet cross sections as functions of View the MathML sourceETjet, jet pseudorapidity, the jet–jet scattering angle, dijet invariant mass and the fraction of the photon energy carried by the dijet system are presented for gluon- and quark-tagged jets. The data exhibit the behaviour expected from the underlying parton dynamics. A value of αs(MZ)αs(MZ) of View the MathML sourceαs(MZ)=0.1176±0.0009(stat.)−0.0026+0.0009(exp.)−0.0072+0.0091(th.) was extracted from the measurements of jet shapes in deep inelastic scattering

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

Multi-Leptons with High Transverse Momentum at HERA

18 pages, 3 figures, revised version with small textual changesEvents with at least two high transverse momentum leptons (electrons or muons) are studied using the H1 and ZEUS detectors at HERA with an integrated luminosity of 0.94 fb^{-1}. The observed numbers of events are in general agreement with the Standard Model predictions. Seven di- and tri-lepton events are observed in e^+p collision data with a scalar sum of the lepton transverse momenta above 100 GeV while 1.94+-0.17 events are expected. Such events are not observed in e^-p collisions for which 1.19+-0.12 are predicted. Total visible and differential di-electron and di-muon photoproduction cross sections are extracted in a restricted phase space dominated by photon-photon collisions

BEAM TESTS OF THE ZEUS BARREL CALORIMETER

A fully compensating uranium-scintillator calorimeter was constructed for the ZEUS detector at HERA. Several of the barrel calorimeter modules were subjected to beam tests at Fermilab before shipping them to DESY for installation. The calibrations of the modules used beams of electrons and hadrons, measuring the uniformity of the response, and checking the resolution. The runs also provided opportunity to test a large fraction of the actual ZEUS calorimeter readout system in an integrated beam environment more than one year before HERA turn on. The experiment utilized two computer controlled mechanical structures. one of which was capable of holding up to four modules in order to study shower containment, and a magnetic spectrometer with a high resolution beam tracking system. During two running periods, beams of 6 to 110 GeV containing e, mu, pi, and pBAR were used. The results show energy resolutions of 35%/square-root E for hadrons and 19%/square-root E for electrons, uniformities at the 1% level, energy nonlinearity less than 1%, and equal response for electrons and hadrons