Publications (168)261.65 Total impact
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ABSTRACT: The 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 < z < 0.9 and 60 < W < 190 GeV as a function of W, z and p T . Here W denotes the photonproton centreofmass energy, z is the fraction of the incident photon energy carried by the meson and p T is the transverse momentum of the meson with respect to the beam axis. The J/ψ cross sections were measured for 0.1 < z < 0.9, 60 < W < 240 GeV and p T > 1 GeV. Theoretical predictions within the nonrelativistic QCD framework including NLO coloursinglet and colouroctet contributions were compared to the data, as were predictions based on the k T factorisation approach.Journal of High Energy Physics 02/2013; 2013(2). DOI:10.1007/JHEP02(2013)071 · 6.22 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Measurements of open charm production cross sections in deepinelastic ep scattering at HERA from the H1 and ZEUS Collaborations are combined. Reduced cross sections sigma_red^{c\bar{c}} for charm production are obtained in the kinematic range of photon virtuality 2.5<Q2<2000 GeV2 and Bjorken scaling variable 0.00003<x<0.05. The combination method accounts for the correlations of the systematic uncertainties among the different data sets. The combined charm data together with the combined inclusive deepinelastic scattering cross sections from HERA are used as input for a detailed NLO QCD analysis to study the influence of different heavy flavour schemes on the parton distribution functions. The optimal values of the charm mass as a parameter in these different schemes are obtained. The implications on the NLO predictions for W^{\pm} and Z production cross sections at the LHC are investigated. Using the fixed flavour number scheme, the running mass of the charm quark is determined.European Physical Journal C 01/2013; 73:2311. DOI:10.1140/epjc/s1005201323113 · 5.44 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The production of Z0 bosons in the reaction ep > eZ0p*, where p* stands for a proton or a lowmass 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 pb1 of integrated luminosity. The Z0 was measured in the hadronic decay mode. The elasticity of the events was ensured by a cut on eta_max < 3.0, where eta_max 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 sigma(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.  [Show abstract] [Hide abstract]
ABSTRACT: A search for singletop production, $ep \rightarrow etX$, has been performed with the ZEUS detector at HERA using data corresponding to an integrated luminosity of $0.37\fbi$. No evidence for top production was found, consistent with the expectation from the Standard Model. Limits were computed for singletop production via flavour changing neutral current transitions. The result was combined with a previous ZEUS result yielding a total luminosity of 0.50fb1. A 95% credibility level upper limit of 0.13 pb was obtained for the cross section at the centreofmass energy of $\sqrt{s}=315\gev$.  [Show abstract] [Hide abstract]
ABSTRACT: Measurements of the cross sections for charged current deep inelastic scattering in e + p collisions with a longitudinally polarised positron beam are presented. The measurements are based on a data sample with an integrated luminosity of 132pb−1 collected with the ZEUS detector at HERA at a centreofmass energy of 318GeV. The total cross section is presented at positive and negative values of the longitudinal polarisation of the positron beams. The singledifferential crosssections dσ/dQ 2, dσ/dx and dσ/dy are presented for Q 2>200GeV2. The reduced crosssection [(s)\tilde]\tilde{\sigma} is presented in the kinematic range 200<Q 2<60 000GeV2 and 0.006<x<0.562. The measurements agree well with the predictions of the Standard Model. The results are used to determine a lower limit on the mass of a hypothetical righthanded W boson.European Physical Journal C 08/2012; 70(4):945963. DOI:10.1140/epjc/s1005201014989 · 5.44 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The production of isolated highenergy photons accompanied by jets has been measured in deep inelastic ep scattering with the ZEUS detector at HERA, using an integrated luminosity of . Measurements were made for exchanged photon virtualities, , in the range 10 to . The photons were measured in the transverseenergy and pseudorapidity ranges and , and the jets were measured in the transverseenergy and pseudorapidity ranges and . Differential cross sections are presented as functions of these quantities. Perturbative QCD predictions give a reasonable description of the shape of the measured cross sections over most of the kinematic range, but the absolute normalisation is typically in disagreement by 20–30%.  [Show abstract] [Hide abstract]
ABSTRACT: A 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 centreofmass energy sqrt(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 < Q2 < 200 GeV2 in photon virtuality, 0.00035 < xIP < 0.09 in proton fractional momentum loss, 0.09 < t < 0.55 GeV2 in squared fourmomentum transfer at the proton vertex and 0.0018 < beta < 0.816 in beta = x/xIP, where x is the Bjorken scaling variable.European Physical Journal C 07/2012; 72:2175. DOI:10.1140/epjc/s100520122175y · 5.44 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: A search for firstgeneration leptoquarks was performed in electronproton and positronproton collisions recorded with the ZEUS detector at HERA in 2003–2007 using an integrated luminosity of 366 pb1. Final states with an electron and jets or with missing transverse momentum and jets were analyzed, searching for resonances or other deviations from the standard model predictions. No evidence for any leptoquark signal was found. The data were combined with data previously taken at HERA, resulting in a total integrated luminosity of 498 pb1. Limits on the Yukawa coupling, λ, of leptoquarks were set as a function of the leptoquark mass for different leptoquark types within the BuchmüllerRücklWyler model. Leptoquarks with a coupling λ=0.3 are excluded for masses up to 699 GeV.  [Show abstract] [Hide abstract]
ABSTRACT: Inclusivejet cross sections have been measured in the reaction ep>e+jet+X for photon virtuality Q2 < 1 GeV2 and gammap centreofmass energies in the region 142 < W(gammap) < 293 GeV with the ZEUS detector at HERA using an integrated luminosity of 300 pb1. Jets were identified using the kT, antikT or SIScone jet algorithms in the laboratory frame. Singledifferential cross sections are presented as functions of the jet transverse energy, ETjet, and pseudorapidity, etajet, for jets with ETjet > 17 GeV and 1 < etajet < 2.5. In addition, measurements of doubledifferential inclusivejet cross sections are presented as functions of ETjet in different regions of etajet. Nexttoleadingorder QCD calculations give a good description of the measurements, except for jets with low ETjet and high etajet. The influence of nonperturbative effects not related to hadronisation was studied. Measurements of the ratios of cross sections using different jet algorithms are also presented; the measured ratios are well described by calculations including up to O(alphas2) terms. Values of alphas(Mz) were extracted from the measurements and the energyscale dependence of the coupling was determined. The value of alphas(Mz) extracted from the measurements based on the kT jet algorithm is alphas(Mz) = 0.1206 +0.0023 0.0022 (exp.) +0.0042 0.0035 (th.); the results from the antikT and SIScone algorithms are compatible with this value and have a similar precision.Nuclear Physics B 05/2012; 864(1). DOI:10.1016/j.nuclphysb.2012.06.006 · 3.95 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Threejet production in deep inelastic ep scattering and photoproduction was investigated with the ZEUS detector at HERA using an integrated luminosity of up to 127 pb1. Measurements of differential cross sections are presented as functions of angular correlations between the three jets in the final state and the protonbeam direction. These correlations provide a stringent test of perturbative QCD and show sensitivity to the contributions from different color configurations. Fixedorder perturbative calculations assuming the values of the color factors CF, CA, and TF 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.  [Show abstract] [Hide abstract]
ABSTRACT: Scaled momentum distributions for the strange hadrons $ K_{\text{S}}^0 $ and $ \Lambda /\bar{\Lambda } $ were measured in deep inelastic ep scattering with the ZEUS detector at HERA using an integrated luminosity of 330 pb−1. The evolution of these distributions with the photon virtuality, Q 2, was studied in the kinematic region 10 < Q 2 < 40000 GeV2 and 0.001 < x < 0.75, where x is the Bjorken scaling variable. Clear scaling violations are observed. Predictions based on different approaches to fragmentation were compared to the measurements. Leadinglogarithm partonshower Monte Carlo calculations interfaced to the Lund string fragmentation model describe the data reasonably well in the whole range measured. Nexttoleadingorder QCD calculations based on fragmentation functions, FFs, extracted from e +e − data alone, fail to describe the measurements. The calculations based on FFs extracted from a global analysis including e +e −, ep and pp data give an improved description. The measurements presented in this paper have the potential to further constrain the FFs of quarks, antiquarks and gluons yielding $ K_{\text{S}}^0 $ and $ \Lambda /\bar{\Lambda } $ strange hadrons.Journal of High Energy Physics 03/2012; 2012(3). DOI:10.1007/JHEP03(2012)020 · 6.22 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The exclusive electroproduction of two pions in the mass range 0.4 < M{\pi}{\pi} < 2.5 GeV has been studied with the ZEUS detector at HERA using an integrated luminosity of 82 pb1. The analysis was carried out in the kinematic range of 2 < Q2 < 80 GeV2, 32 < W < 180 GeV and t < 0.6 GeV2, where Q2 is the photon virtuality, W is the photonproton centreofmass energy and t is the squared fourmomentum transfer at the proton vertex. The twopion invariantmass distribution is interpreted in terms of the pion electromagnetic form factor, F(M{\pi}{\pi}), assuming that the studied mass range includes the contributions of the {\rho}, {\rho}' and {\rho}" vectormeson states. The masses and widths of the resonances were obtained and the Q2 dependence of the crosssection ratios {\sigma}({\rho}' \rightarrow {\pi}{\pi})/{\sigma}({\rho}) and {\sigma}({\rho}" \rightarrow {\pi}{\pi})/{\sigma}({\rho}) was extracted. The pion form factor obtained in the present analysis is compared to that obtained in e+e \rightarrow {\pi}+{\pi}.European Physical Journal C 11/2011; 72(1). DOI:10.1140/epjc/s1005201218695 · 5.44 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: A search for singletop production, $ep \rightarrow etX$, has been performed with the ZEUS detector at HERA using data corresponding to an integrated luminosity of $0.37\fbi$. No evidence for top production was found, consistent with the expectation from the Standard Model. Limits were computed for singletop production via flavour changing neutral current transitions. The result was combined with a previous ZEUS result yielding a total luminosity of 0.50fb1. A 95% credibility level upper limit of 0.13 pb was obtained for the cross section at the centreofmass energy of $\sqrt{s}=315\gev$.  [Show abstract] [Hide abstract]
ABSTRACT: Scaled momentum distributions for the strange hadrons K0s and Lambda/bar Lambda were measured in deep inelastic ep scattering with the ZEUS detector at HERA using an integrated luminosity of 330 pb1. The evolution of these distributions with the photon virtuality, Q2, was studied in the kinematic region 10<Q2<40000 GeV2 and 0.001<x<0.75, where x is the Bjorken scaling variable. Clear scaling violations are observed. Predictions based on different approaches to fragmentation were compared to the measurements. Leadinglogarithm partonshower Monte Carlo calculations interfaced to the Lund string fragmentation model describe the data reasonably well in the whole range measured. Nexttoleadingorder QCD calculations based on fragmentation functions, FFs, extracted from e+e data alone, fail to describe the measurements. The calculations based on FFs extracted from a global analysis including e+e, ep and pp data give an improved description. The measurements presented in this paper have the potential to further constrain the FFs of quarks, antiquarks and gluons yielding K0s and Lambda/bar Lambda strange hadrons.  [Show abstract] [Hide abstract]
ABSTRACT: The exclusive photoproduction reaction gamma p > Upsilon(1S) p has been studied with the ZEUS detector in ep collisions at HERA using an integrated luminosity of 468 pb^1. The measurement covers the kinematic range 60<W<220 GeV and Q^2<1 GeV^2, where W is the photonproton centreofmass energy and Q^2 is the photon virtuality. The exponential slope, b, of the t dependence of the cross section, where t is the squared fourmomentum transfer at the proton vertex, has been measured, yielding b = 4.3 +2.0 1.3 (stat.) +0.5 0.6 (syst.) GeV^2. This constitutes the first measurement of the t dependence of the gamma p > Upsilon(1S) p cross section.Physics Letters B 11/2011; 708(12). DOI:10.1016/j.physletb.2012.01.009 · 6.02 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Photoproduction of beauty and charm quarks in events with at least two jets has been measured with the ZEUS detector at HERA using an integrated luminosity of 133 $pb^{1}$. The fractions of jets containing b and c quarks were extracted using the invariant mass of charged tracks associated with secondary vertices and the decaylength significance of these vertices. Differential cross sections as a function of jet transverse momentum, $p_{T}^{\text{jet}}$, and pseudorapidity, $\eta^{\text{jet}}$, were measured. The data are compared with previous measurements and are well described by nexttoleadingorder QCD predictions. 
Article: Measurement of beauty production in deep inelastic scattering at HERA using decays into electrons
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ABSTRACT: The production of beauty quarks in ep interactions has been studied with the ZEUS detector at HERA for exchanged fourmomentum squared Q 2>10GeV2, using an integrated luminosity of 363 pb−1. The beauty events were identified using electrons from semileptonic b decays with a transverse momentum 0.9 < pTe < 80.9 < p_{T}^{e} < 8GeV and pseudorapidity η e <1.5. Cross sections for beauty production were measured and compared with nexttoleadingorder QCD calculations. The beauty contribution to the proton structure function F 2 was extracted from the doubledifferential cross section as a function of Bjorkenx and Q 2.European Physical Journal C 01/2011; 71(2):115. DOI:10.1140/epjc/s100520111573x · 5.44 Impact Factor 
Article: Study of tauPair Production at HERA
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ABSTRACT: Journal articleJournal of High Energy Physics 01/2011; DOI:10.1007/JHEP02(2011)117 · 6.22 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Journal article  [Show abstract] [Hide abstract]
ABSTRACT: Single and doubledifferential inclusive dijet cross sections in neutral current deep inelastic ep scattering have been measured with the ZEUS detector using an integrated luminosity of 374pb−1. The measurement was performed at large values of the photon virtuality, Q 2, between 125 and 20 000GeV2. The jets were reconstructed with the k T cluster algorithm in the Breit reference frame and selected by requiring their transverse energies in the Breit frame, EjetT,BE^{\rm jet}_{T,{\rm B}}, to be larger than 8GeV. In addition, the invariant mass of the dijet system, MjjM_{\rm jj}, was required to be greater than 20GeV. The cross sections are described by the predictions of nexttoleadingorder QCD.European Physical Journal C 10/2010; 70(4):965982. DOI:10.1140/epjc/s1005201015042 · 5.44 Impact Factor
Publication Stats
730  Citations  
261.65  Total Impact Points  
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Institutions

2012

INFN  Istituto Nazionale di Fisica Nucleare
Frascati, Latium, Italy


2008

Argonne National Laboratory
Lemont, Illinois, United States
