Publications (309)37.54 Total impact
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ABSTRACT: In this extended analysis using the ZEUS detector at HERA, the photoproduction of isolated photons together with a jet is measured for different ranges of the fractional photon energy, $x_\gamma^{\mathrm{meas}}$, contributing to the photonjet final state. Cross sections are evaluated in the photon transverseenergy and pseudorapidity ranges $6 < E_T^{\gamma} < 15$ GeV and $0.7 < \eta^{\gamma} < 0.9$, and for jet transverseenergy and pseudorapidity ranges $4 < E_T^{\rm jet} < 35$ GeV and $1.5 < \eta^{\rm jet} < 1.8$, for an integrated luminosity of 374 $\mathrm{pb}^{1}$. The kinematic observables studied comprise the transverse energy and pseudorapidity of the photon and the jet, the azimuthal difference between them, the fraction of proton energy taking part in the interaction, and the difference between the pseudorapidities of the photon and the jet. Higherorder theoretical calculations are compared to the results.05/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The production of beauty and charm quarks in ep interactions has been studied with the ZEUS detector at HERA for exchanged fourmomentum squared 5 < Q^2 < 1000 GeV^2 using an integrated luminosity of 354 pb^{1}. The beauty and charm content in events with at least one jet have been 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 Q^2, Bjorken x, jet transverse energy and pseudorapidity were measured and compared with nexttoleadingorder QCD calculations. The beauty and charm contributions to the proton structure functions were extracted from the doubledifferential cross section as a function of x and Q^2. The running beautyquark mass, m_b at the scale m_b, was determined from a QCD fit at nexttoleading order to HERA data for the first time and found to be 4.07 \pm 0.14 (fit} ^{+0.01}_{0.07} (mod.) ^{+0.05}_{0.00} (param.) ^{+0.08}_{0.05} (theo) GeV.05/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The cross sections for the photoproduction of $D^*$ mesons have been measured with the ZEUS detector at HERA at three different ep centreofmass energies, $\sqrt{s}$, of 318, 251 and 225 GeV. For each data set, $D^*$ mesons were required to have transverse momentum, $p_T^{D^*}$, and pseudorapidity, $\eta^{D^*}$, in the ranges $1.9 < p_T^{D^*} < 20$ GeV and $\eta^{D^*}<1.6$. The events were required to have a virtuality of the incoming photon, $Q^2$, of less than 1 GeV$^2$. The dependence on $\sqrt{s}$ was studied by normalising to the highstatistics measurement at $\sqrt{s} =318$ GeV. This led to the cancellation of a number of systematic effects both in data and theory. Predictions from nexttoleadingorder QCD describe the $\sqrt{s}$ dependence of the data well.05/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The reduced cross sections for $e^{+}p$ deep inelastic scattering have been measured with the ZEUS detector at HERA at three different centreofmass energies, $318$, $251$ and $225$ GeV. The cross sections, measured double differentially in Bjorken $x$ and the virtuality, $Q^2$, were obtained in the region $0.13\ \leq\ y\ \leq\ 0.75$, where $y$ denotes the inelasticity and $5\ \leq\ Q^2\ \leq\ 110$ GeV$^2$. The proton structure functions $F_2$ and $F_L$ were extracted from the measured cross sections.04/2014; 
Article: Measurement of neutral current e+/p cross sections at high Bjorken x with the ZEUS detector
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ABSTRACT: The neutral current e+/p cross section has been measured up to values of Bjorken x of approximately 1 with the ZEUS detector at HERA using an integrated luminosity of 187 inv. pb of ep and 142 inv. pb of e+p collisions at sqrt(s) = 318GeV. Differential cross sections in x and Q2, the exchanged boson virtuality, are presented for Q2 geq 725GeV2. An improved reconstruction method and greatly increased amount of data allows a finer binning in the highx region of the neutral current cross section and leads 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.12/2013;  [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.10/2012; 
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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.05/2012;  [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  EUR PHYS J C. 11/2011;  [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 $\sqrt{s}=315\gev$.11/2011;  [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.11/2011;  [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.11/2011;  [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.European Physical Journal C  EUR PHYS J C. 04/2011; 71(5). 
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 > 10 GeV^2, 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 < p_T^e < 8 GeV and pseudorapidity eta^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^2.01/2011;  [Show abstract] [Hide abstract]
ABSTRACT: Beauty production in deep inelastic scattering with events in which a muon and a jet are observed in the final state has been measured with the ZEUS detector at HERA using an integrated luminosity of 114 pb^1. The fraction of events with beauty quarks in the data was determined using the distribution of the transverse momentum of the muon relative to the jet. The cross section for beauty production was measured in the kinematic range of photon virtuality, Q^2 > 2 Gev^2, and inelasticity, 0.05 < y < 0.7, with the requirement of a muon and a jet. Total and differential cross sections are presented and compared to QCD predictions. The beauty contribution to the structure function F_2 was extracted and is compared to theoretical predictions. Comment: 24 pages, 5 figures05/2010;  [Show abstract] [Hide abstract]
ABSTRACT: For the first time, differential inclusivejet cross sections have been measured in neutral current deep inelastic ep scattering using the antikT and SIScone algorithms. The measurements were made for boson virtualities Q2>125 GeV2 with the ZEUS detector at HERA using an integrated luminosity of 82 pb−1 and the jets were identified in the Breit frame. The performance and suitability of the jet algorithms for their use in hadronlike reactions were investigated by comparing the measurements to those performed with the kT algorithm. Nexttoleadingorder QCD calculations give a good description of the measurements. 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(αs3) terms. Values of αs(MZ) were extracted from the data; the results are compatible with and have similar precision to the value extracted from the kT analysis.01/2010;  01/2010;
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ABSTRACT: The protondissociative diffractive photoproduction of J/ψ mesons has been studied in ep collisions with the ZEUS detector at HERA using an integrated luminosity of 112 pb−1. The cross section is presented as a function of the photonproton centreofmass energy and of the squared fourmomentum transfer at the proton vertex. The results are compared to perturbative QCD calculations. KeywordsLeptonNucleon ScatteringJournal of High Energy Physics 01/2010; 2010(5):136. · 5.62 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Charm production in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 120 pb1. The hadronic decay channels D + > K S 0 pi +, Lambda c + > pK S 0 and Lambda c + > Lambda pi +, and their charge conjugates, were reconstructed. The presence of a neutral strange hadron in the final state reduces the combinatorial background and extends the measured sensitivity into the low transverse momentum region. The kinematic range is 0 < p T ( D +, Lambda c +) < 10 GeV,  eta( D +, Lambda c +) < 1 .6, 1.5 < Q 2 < 1000 GeV2 and 0 .02 < y < 0.7. Inclusive and differential cross sections for the production of D + mesons are compared to nexttoleadingorder QCD predictions. The fraction of c quarks hadronising into Lambda c + baryons is extracted.01/2010;  01/2010; 1:1.
Publication Stats
604  Citations  
37.54  Total Impact Points  
Top Journals
Institutions

1993–2007

Argonne National Laboratory
Lemont, Illinois, United States


2003

McGill University
 Department of Physics
Montréal, Quebec, Canada


2

HumboldtUniversität zu Berlin
 Department of Physics
Berlin, Land Berlin, Germany
