Publications (42)114.88 Total impact
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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.Journal of High Energy Physics 05/2014; 2014(8). DOI:10.1007/JHEP08(2014)023 · 6.22 Impact Factor  [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.Journal of High Energy Physics 05/2014; 2014(10). DOI:10.1007/JHEP09(2014)127 · 6.22 Impact Factor  [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.Physical Review D 12/2013; 89(7). DOI:10.1103/PhysRevD.89.072007 · 4.86 Impact Factor  [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.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.
Publication Stats
60  Citations  
114.88  Total Impact Points  
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Institutions

2013–2014

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


2012

INFN  Istituto Nazionale di Fisica Nucleare
Frascati, Latium, Italy


2010

Kiev National Linguistic University
Kievo, Kyiv City, Ukraine
