25,920 research outputs found
Study of proton parton distribution functions at high x using ZEUS data
No full textAt large values of x the parton distribution functions (PDFs) of the proton are poorly constrained and there are considerable variations between different global fits. Data at such high x have already been published by the ZEUS Collaboration, but not yet used in PDF extractions. A technique for comparing predictions based on different PDF sets to the observed number of events in the ZEUS data is presented. It is applied to compare predictions from the most commonly used PDFs to published ZEUS data at high Bjorken x. A wide variation is found in the ability of the PDFs to predict the observed results. A scheme for including the ZEUS high-x data in future PDF extractions is discussed
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
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
The ZEUS long term data preservation project
No full textThe ZEUS data preservation (ZEUS DP) project assures continued access to the data and documentation related to the experiment. It aims toprovide the ability to continue the generation of valuable scientific results from these data in the future. This talk presents analysis opportunities within the ZEUS DP project and its benefits for the physics community. The implications of the preserved data are discussed in the context of currentdata analyses, verification of contemporary and future theoretical models and the planning of future experiments and analyses. The detailed documentation on the data preservation effort can serve as an example for the data preservation efforts in current and future experiments
Combined inclusive diffractive cross sections measured with forward proton spectrometers in deep inelastic ep scattering at HERA
No full textA combination of the inclusive diffractive cross section measurements made by the H1 and ZEUS Collaborations at HERA is presented. The analysis uses samples of diffractive deep inelastic ep scattering data at a centre-of-mass energy √s= 318 Gev where leading protons are detected by dedicated spectrometers. Correlations of systematic uncertainties are taken into account, resulting in an improved precision of the cross section measurement which reaches 6 % for the most precise points. The combined data cover the range 2.5 < Q 2 < 200 GeV 2 in photon virtuality, 0.00035 < xP < 0.09 in proton fractional momentum loss, 0.09 <{pipe}t{pipe}< 0.55 GeV 2 in squared four-momentum transfer at the proton vertex and 0.0018 < β <0.816 in β=x/xP, where x is the Bjorken scaling variable. © 2012 The Author(s)
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
Measurement of neutral current cross sections at high Bjorken-x with the ZEUS detector at HERA.
No full textTreatment of QED corrections in jet production in deep inelastic scattering at ZEUS
No full textA new measurement of inclusive jet production in deep inelastic scattering was recently published by the ZEUS Collaboration. This contribution presents a detailed discussion of the treatment of higher-order QED effects in this measurement. A comprehensive treatment of these effects is crucial for a more direct comparison between ever more precise measurements and theoretical calculations. The present analysis is the only measurement of jet production in deep inelastic scattering that can be compared to full NNLO QCD + NLO electroweak predictions
Measurement of neutral current cross sections at high Bjorken x with the ZEUS detector
No full textThe latest results of the ZEUS collaboration on the high Q2, the exchanged boson virtuality, high Bjorken x region up to values of x = 1 are presented. Differential cross sections in x and Q2 are given for Q2 > 725 GeV2. An improved reconstruction method and a substantially increased amount of data allow a finer binning in the high-x region of the neutral current cross section and lead to a measurement with much improved precision compared to a similar earlier analysis. The measurements are compared to Standard Model expectations based on a variety of recent parton distribution functions
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