Publications (303)353.41 Total impact
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ABSTRACT: The exclusive deep inelastic electroproduction of $\psi(2S)$ and $J/\psi(1S)$ at an $ep$ centreofmass energy of 317 GeV has been studied with the ZEUS detector at HERA in the kinematic range $2 < Q^2 < 80$ GeV$^2$, $30 < W < 210$ GeV and $t < 1$ GeV$^2$, where $Q^2$ is the photon virtuality, $W$ is the photonproton centreofmass energy and $t$ is the squared fourmomentum transfer at the proton vertex. The data for $2 < Q^2 < 5$ GeV$^2$ were taken in the HERA I running period and correspond to an integrated luminosity of 114 pb$^{1}$. The data for $5 < Q^2 < 80$ GeV$^2$ are from both HERA I and HERA II periods and correspond to an integrated luminosity of 468 pb$^{1}$. The decay modes analysed were $\mu^+\mu^$ and $J/\psi(1S) \,\pi^+\pi^$ for the $\psi(2S)$ and $\mu^+\mu^$ for the $J/\psi(1S)$. The crosssection ratio $\sigma_{\psi(2S)}/\sigma_{J/\psi(1S)}$ has been measured as a function of $Q^2, W$ and $t$. The results are compared to predictions of QCDinspired models of exclusive vectormeson production.  [Show abstract] [Hide abstract]
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.  [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.  [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.  [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. 
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.  [Show abstract] [Hide abstract]
ABSTRACT: The production of $D^{*\pm}$ mesons in deep inelastic $ep$ scattering has been measured for exchanged photon virtualities $ 5<Q^2<1000 \gev^2 $, using an integrated luminosity of 363 pb$^{1}$ with the ZEUS detector at HERA. Differential cross sections have been measured and compared to nexttoleadingorder QCD calculations. The crosssections are used to extract the charm contribution to the proton structure functions, expressed in terms of the reduced charm cross section, $\sigma_{\rm red}^{c\bar{c}}$. Theoretical calculations based on fits to inclusive HERA data are compared to the results.  [Show abstract] [Hide abstract]
ABSTRACT: Measurements of neutral current cross sections for deep inelastic scattering in e(+)p collisions at HERA with a longitudinally polarized positron beam are presented. The singledifferential crosssections d sigma=dQ(2), d sigma=dx and d sigma=dy and the reduced cross section (sigma) over tilde are measured in the kinematic region Q(2) >185 GeV2 and y<0.9, where Q(2) is the fourmomentum transfer squared, x the Bjorken scaling variable and y the inelasticity of the interaction. The measurements are performed separately for positively and negatively polarized positron beams. The measurements are based on an integrated luminosity of 135.5 pb(1) collected with the ZEUS detector in 2006 and 2007 at a centerofmass energy of 318 GeV. The structure functions <(F3)over tilde> and F3(gamma Z) are determined by combining the e(+)p results presented in this paper with previously published e()p neutral current results. The asymmetry parameter A(+) is used to demonstrate the parity violation predicted in electroweak interactions. The measurements are well described by the predictions of the Standard Model.  [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: The production of the excited charm mesons D_1(2420) and D^*_2(2460) in ep collisions has been measured with the ZEUS detector at HERA using an integrated luminosity of 373 pb^{1}. The masses of the neutral and charged states, the widths of the neutral states, and the helicity parameter of D_1(2420)^{0} were determined and compared with other measurements and with theoretical expectations. The measured helicity parameter of the D^0_1 allows for some mixing of S and Dwaves in its decay to D^{*\pm}\pi^{\mp}. The result is also consistent with a pure Dwave decay. Ratios of branching fractions of the two decay modes of the D^*_2(2460)^0 and D^*_2(2460)^{\pm} states were measured and compared with previous measurements. The fractions of charm quarks hadronising into D_1 and D^{*}_2 were measured and are consistent with those obtained in e^+ e^ annihilations.  [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.  [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}.  [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.  [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.  [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 pb−1. The hadronic decay channels D + → K S 0 π +, Λ c + → pK S 0 and Λ c + → Λπ +, 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 +, Λ c +) < 10 GeV, η(D +, Λ 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 Λ c + baryons is extracted. KeywordsLeptonNucleon Scattering  [Show abstract] [Hide abstract]
ABSTRACT: Charged particle production has been studied in neutral current deep inelastic ep scattering with the ZEUS detector at HERA using an integrated luminosity of 0.44 fb−1. Distributions of scaled momenta in the Breit frame are presented for particles in the current fragmentation region. The evolution of these spectra with the photon virtuality, Q 2, is described in the kinematic region 10 < Q 2 < 41000Ge V2. Nexttoleadingorder and modified leadinglogapproximation QCD calculations as well as predictions from Monte Carlo models are compared to the data. The results are also compared to e + e − annihilation data. The dependences of the pseudorapidity distribution of the particles on Q 2 and on the energy in the γp system, W, are presented and interpreted in the context of the hypothesis of limiting fragmentation. KeywordsLeptonNucleon Scattering  [Show abstract] [Hide abstract]
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 Scattering
Publication Stats
3k  Citations  
353.41  Total Impact Points  
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Institutions

2014

Tel Aviv University
Tell Afif, Tel Aviv, Israel


2010

Japan Synchrotron Radiation Research Institute (JASRI)
Tatsuno, Hyōgo, Japan


19962010

Università degli Studi di Salerno
Fisciano, Campania, Italy 
Weizmann Institute of Science
Rhovot, Central District, Israel 
Deutsches ElektronenSynchrotron
Hamburg, Hamburg, Germany


20052007

HumboldtUniversität zu Berlin
Berlín, Berlin, Germany


19932007

Argonne National Laboratory
 Division of Physics
Lemont, Illinois, United States


19932004

University of Freiburg
Freiburg, BadenWürttemberg, Germany


2003

Jagiellonian University
Cracovia, Lesser Poland Voivodeship, Poland


1989

University of Bristol
Bristol, England, United Kingdom
