1,721,821 research outputs found
Measurement of neutral current cross sections at high Bjorken-x with the ZEUS detector at HERA.
No full text
Angular correlations in three-jet events in ep collisions at HERA
No full textThree-jet production in deep inelastic ep scattering and photoproduction was investigated with the ZEUS detector at HERA using an integrated luminosity of up to 127pb -1. Measurements of differential cross sections are presented as functions of angular correlations between the three jets in the final state and the proton-beam direction. These correlations provide a stringent test of perturbative QCD and show sensitivity to the contributions from different color configurations. Fixed-order perturbative calculations assuming the values of the color factors C F, C A, and T F as derived from a variety of gauge groups were compared to the measurements to study the underlying gauge group symmetry. The measured angular correlations in the deep inelastic ep scattering and photoproduction regimes are consistent with the admixture of color configurations as predicted by SU(3) and disfavour other symmetry groups, such as SU(N) in the limit of large N. © 2012 American Physical Society
Production of Z0 bosons in elastic and quasi-elastic ep collisions at HERA
No full textThe production of Z0 bosons in the reaction ep→eZ0p(∗), where p(∗) stands for a proton or a low- mass nucleon resonance, has been studied in ep collisions at HERA using the ZEUS detector. The analysis is based on a data sample collected between 1996 and 2007, amounting to 496 pb−1 of integrated luminosity. The Z0 was measured in the hadronic decay mode. The elasticity of the events was ensured by a cut on ηmax < 3.0, where ηmax is the maximum pseudorapidity of energy deposits in the calorimeter defined with respect to the proton beam direction. A signal was observed at the Z0 mass. The cross section of the reaction ep → eZ0p(∗) was measured to be σ(ep → eZ0p(∗)) =0.13 ± 0.06(stat.) ± 0.01(syst.) pb, in agreement with the Standard Model prediction of 0.16 pb. This
is the first measurement of Z0 production in ep collisions
Measurement of inelastic J/ψ and ψ′ photoproduction at HERA
No full textThe cross sections for inelastic photoproduction of J/ψ and ψ′ mesons have been measured in ep collisions with the ZEUS detector at HERA, using an integrated luminosity of 468 pb−1 collected in the period 1996–2007. The ψ′ to J/ψ cross section ratio was measured in the range 0.55 1 GeV. Theoretical predictions within the non- relativistic QCD framework including NLO colour-singlet and colour-octet contributions were compared to the data, as were predictions based on the kT -factorisation approach
Measurement of charm fragmentation fractions in photoproduction at HERA
No full textThe production of D 0, D *+, D +, Ds + and Λc + charm hadrons and their antiparticles in ep scattering at HERA has been studied with the ZEUS detector, using a total integrated luminosity of 372 pb-1. The fractions of charm quarks hadronising into a particular charm hadron were derived. In addition, the ratio of neutral to charged D-meson production rates, the fraction of charged D mesons produced in a vector state, and the stangeness-suppression factor have been determined. The measurements have been performed in the photoproduction regime. The charm hadrons were reconstructed in the range of transverse momentum p T > 3.8 GeV and pseudorapidity |η| < 1.6. The charm fragmentation fractions are compared to previous results from HERA and from e + e - experiments. The data support the hypothesis that fragmentation is independent of the production process
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