Publications (48)200.34 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: A combination is presented of all inclusive deep inelastic cross sections previously published by the H1 and ZEUS collaborations at HERA for neutral and charged current (Formula presented.) scattering for zero beam polarisation. The data were taken at proton beam energies of 920, 820, 575 and 460 GeV and an electron beam energy of 27.5 GeV. The data correspond to an integrated luminosity of about 1 fb(Formula presented.) and span six orders of magnitude in negative fourmomentumtransfer squared, (Formula presented.), and Bjorken x. The correlations of the systematic uncertainties were evaluated and taken into account for the combination. The combined cross sections were input to QCD analyses at leading order, nexttoleading order and at nexttonexttoleading order, providing a new set of parton distribution functions, called HERAPDF2.0. In addition to the experimental uncertainties, model and parameterisation uncertainties were assessed for these parton distribution functions. Variants of HERAPDF2.0 with an alternative gluon parameterisation, HERAPDF2.0AG, and using fixedflavournumber schemes, HERAPDF2.0FF, are presented. The analysis was extended by including HERA data on charm and jet production, resulting in the variant HERAPDF2.0Jets. The inclusion of jetproduction cross sections made a simultaneous determination of these parton distributions and the strong coupling constant possible, resulting in (Formula presented.). An extraction of (Formula presented.) and results on electroweak unification and scaling violations are also presented. 
Article: Combination of differential D∗± crosssection measurements in deepinelastic ep scattering at HERA
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ABSTRACT: H1 and ZEUS have published singledifferential cross sections for inclusive D ∗±meson production in deepinelastic ep scattering at HERA from their respective final data sets. These cross sections are combined in the common visible phasespace region of photon virtuality Q 2> 5 GeV2, electron inelasticity 0.02 < y < 0.7 and the D ∗± meson’s transverse momentum p T(D ∗) > 1.5 GeV and pseudorapidity η(D ∗) < 1.5. The combination procedure takes into account all correlations, yielding significantly reduced experimental uncertainties. Doubledifferential cross sections d2σ/dQ 2dy are combined with earlier D ∗± data, extending the kinematic range down to Q 2> 1.5 GeV2. Perturbative nexttoleadingorder QCD predictions are compared to the results.  [Show abstract] [Hide abstract]
ABSTRACT: Production of exclusive dijets in diffractive deep inelastic $e^\pm p$ scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 372 pb$^{1}$. The measurement was performed for $\gamma^*p$ centreofmass energies in the range $90 < W < 250$ GeV and for photon virtualities $Q^2 > 25$ GeV$^2$. Energy and transverseenergy flows around the jet axis are presented. The cross section is presented as a function of $\beta$ and $\phi$, where $\beta=x/x_{\rm I\!P}$, $x$ is the Bjorken variable and $x_{\rm I\!P}$ is the proton fractional longitudinal momentum loss. The angle $\phi$ is defined by the $\gamma^*$dijet plane and the $\gamma^*e^\pm$ plane in the rest frame of the diffractive final state. The $\phi$ cross section is measured in bins of $\beta$. The results are compared to predictions from models based on different assumptions about the nature of the diffractive exchange.  [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.  [Show abstract] [Hide abstract]
ABSTRACT: The photoproduction of isolated photons, both inclusive and together with a jet, has been measured with the ZEUS detector at HERA using an integrated luminosity of 374 pb(1). Differential cross sections are presented in the isolatedphoton transverseenergy and pseudorapidity ranges 6 < ET(gamma) < 15 GeV and 0.7 < eta(gamma) < 0.9, and for jet transverseenergy and pseudorapidity ranges 4 < ET(jet) < 35 GeV and 1.5 < eta(jet) < 1.8, for exchangedphoton virtualities Q(2) < 1 GeV2. Differential cross sections are also presented for inclusive isolatedphoton production as functions of the transverse energy and pseudorapidity of the photon. Higherorder theoretical calculations are compared to the results. (C) 2014 The Authors. Published by Elsevier B.V.  [Show abstract] [Hide abstract]
ABSTRACT: The production of D *± mesons in deep inelastic ep scattering has been measured for exchanged photon virtualities 5 < Q 2 < 1000 GeV2, 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, \( \sigma_{\mathrm{red}}^{{c\overline{c}}} \). Theoretical calculations based on fits to inclusive HERA data are compared to the results. 
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 0, D *+, D +, \( D_s^{+} \) and \( \Lambda_c^{+} \) 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 Dmeson production rates, the fraction of charged D mesons produced in a vector state, and the stangenesssuppression 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. 
Article: Measurement of D ± production in deep inelastic ep scattering with the ZEUS detector at HERA
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ABSTRACT: Charm production in deep inelastic ep scattering was measured with the ZEUS detector using an integrated luminosity of 354 pb−1. Charm quarks were identified by reconstructing D ± mesons in the D ± → K ∓π±π± decay channel. Lifetime information was used to reduce combinatorial background substantially. Differential cross sections were measured in the kinematic region 5 < Q 2< 1000 GeV2, 0.02 < y < 0.7, 1.5 < p T (D ±) < 15 GeV and η(D ±) < 1.6, where Q 2 is the photon virtuality, y is the inelasticity, and p T (D ±) and η(D ±) are the transverse momentum and the pseudorapidity of the D ± meson, respectively. Nexttoleadingorder QCD predictions are compared to the data. The charm contribution, $ F_2^{{c\overline{c}}} $ , to the proton structurefunction F 2 was extracted.  [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: Measurements of open charm production cross sections in deepinelastic ep scattering at HERA from the H1 and ZEUS Collaborations are combined. Reduced cross sections \(\sigma_{\rm red}^{c\bar{c}}\) for charm production are obtained in the kinematic range of photon virtuality 2.5≤Q 2≤2000 GeV2 and Bjorken scaling variable 3⋅10−5≤x≤5⋅10−2. 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 ± 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.  [Show abstract] [Hide abstract]
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.  [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.  [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%.
Publication Stats
191  Citations  
200.34  Total Impact Points  
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Institutions

20132014

National Taras Shevchenko University of Kyiv
 Department of Nuclear Physics
Kievo, Kyiv City, Ukraine


20122014

National Academy of Sciences of Ukraine
 Institute for Nuclear Research
Kievo, Kyiv City, Ukraine


20102012

National Technical University of Ukraine Kiev Polytechnic Institute
Kievo, Kyiv City, Ukraine
