(SVD-2 Collaboration) A. G. Afonin, E. N. Ardashev, V. F. Golovkin, S. N. Golovnya, S. A. Gorokhov, A. A. Kiryakov, A. G. Kholodenko, V. V. Konstantinov, L. L. Kurchaninov, I. S. Lobanov, E. V. Lobanova, G. A. Mitrofanov, V. S. Petrov, A. V. Pleskach, M. K. Polkovnikov, V. N. Riadovikov*, V. N. Ronzhin, V. A. Senko,N. A. Shalanda, M. M. Soldatov, Yu. P. Tsyupa, A. P. Vorobiev, V. I. Yakimchuk, and V. N. Zapolskii∗ IHEP, Protvino, Moscow region, Russia.

(EHS/NA22 Collaboration) 1 Institute of Physics, AM-375036 Yerevan, Armenia 2 Institute of Particle Physics, Hua-Zhong Normal University, Wuhan 430070, China 3 Department of Physics, University of Antwerp, B-2610 Wilrijk, Belgium 4 Centro Brasileiro de Pesquisas Fisicas, BR-22290 Rio de Janeiro, Brazil 5 Radboud University Nijmegen/NIKHEF, NL-6525 ED Nijmegen, The Netherlands 6 Institute for High Energy Physics of Tbilisi State University, GE-380086 Tbilisi, Georgia; now at Northwestern Univ., Evanston, U.S.A. 7 Scobeltsyn Institute of Nuclear Physics, Lomonosow Moscow State University, RU-119899 Moscow, Russia Now at DESY, Hamburg, Germany Boost invariance and multiplicity dependence of the charge balance function are studied in πp and Kp collisions at 250 GeV/c incident beam momentum. Charge balance, as well as charge fluctuations, are found to be boost invariant over the whole rapidity region, but both depend on the size of the rapidity window. It is also found that the balance function becomes narrower with increasing multiplicity, consistent with the narrowing of the balance function when centrality and/or system size increase, as observed in current relativistic heavy ion experiments.

This paper presents the result of a search for a narrow strange baryonic state in the invariant-mass distribution of $pK^0_S(\overline{p}K^0_S)$ in HERA II data (2003-2007). The search was performed in the deep inelastic scattering (DIS) data with photon virtuality, $Q^2$, between 20 and 100 GeV. The analysis in HERA II period has improvements over the previous ZEUS analysis in HERA I period (1996-2000). These consist of large statistics and improved particle identification performance by using both of the CTD $dE/dx$ and the MVD $dE/dx$ in this search. Contrary to evidence for such an exotic state around 1.52 GeV in the HERA I data, no such state is found in this analysis. The upper limits on the production cross section are set at 95% confidence level.

The exclusive deep inelastic electroproduction of ψ(2S) and J/ψ(1S) at an ep centre-of-mass energy of 317 GeV has been studied with the ZEUS detector at HERA in the kinematic range 2

The exclusive deep inelastic electroproduction of ψ(2S) and J/ψ(1S) at an ep centre-of-mass 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 photon-proton centre-of-mass energy and t is the squared four-momentum 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 μ^+μ^- and J/ψ(1S) π^+π^- for the ψ(2S) and μ^+μ^- for the J/ψ(1S). The cross-section ratio σ_ψ(2S)/σ_J/ψ(1S) has been measured as a function of Q^2, W and t. The results are compared to predictions of QCD-inspired models of exclusive vector-meson production.

The high-precision HERA data allows searches up to TeV scales for beyond the Standard Model contributions to electron-quark scattering. Combined measurements of the inclusive deep inelastic cross sections in neutral and charged current ep scattering corresponding to a luminosity of around 1 fb(-1) have been used in this analysis. A new approach to the beyond the Standard Model analysis of the inclusive ep data is presented; simultaneous fits of parton distribution functions together with contributions of "new physics" processes were performed. Results are presented considering a finite radius of quarks within the quark form-factor model. The resulting 95% C.L. upper limit on the effective quark radius is 0.43.10(-16) cm. (C) 2016 CERN for the benefit of the ZEUS Collaboration. Published by Elsevier B.V.

A simultaneous fit of parton distribution functions (PDFs) and electroweak parameters to HERA data on deep inelastic scattering is presented. The input data are the neutral current and charged current inclusive cross sections which were previously used in the QCD analysis leading to the HERAPDF2.0 PDFs. In addition, the polarisation of the electron beam was taken into account for the ZEUS data recorded between 2004 and 2007. Results on the vector and axial-vector couplings of the Z boson to u- and d-type quarks, on the value of the electroweak mixing angle and the mass of the W boson are presented. The values obtained for the electroweak parameters are in agreement with Standard Model predictions.

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 \(e^{\pm }p\) 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\(^{-1}\) and span six orders of magnitude in negative four-momentum-transfer squared, \(Q^2\), 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, next-to-leading order and at next-to-next-to-leading 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 fixed-flavour-number 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 jet-production cross sections made a simultaneous determination of these parton distributions and the strong coupling constant possible, resulting in \(\alpha _s(M_Z^2)=0.1183 \pm 0.0009 \mathrm{(exp)} \pm 0.0005\mathrm{(model/parameterisation)} \pm 0.0012\mathrm{(hadronisation)} ^{+0.0037}_{-0.0030}\mathrm{(scale)}\). An extraction of \(xF_3^{\gamma Z}\) and results on electroweak unification and scaling violations are also presented.

H1 and ZEUS have published single-differential cross sections for inclusive D ∗±-meson production in deep-inelastic ep scattering at HERA from their respective final data sets. These cross sections are combined in the common visible phase-space 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. Double-differential cross sections d2 σ/dQ 2dy are combined with earlier D ∗± data, extending the kinematic range down to Q 2 > 1.5 GeV2. Perturbative next-to-leading-order QCD predictions are compared to the results.

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 isolated-photon transverse-energy and pseudorapidity ranges 6 < E-T(gamma) < 15 GeV and -0.7 < eta(gamma) < 0.9, and for jet transverse-energy and pseudorapidity ranges 4 < E-T(jet) < 35 GeV and -1.5 < eta(jet) < 1.8, for exchanged-photon virtualities Q(2) < 1 GeV2. Differential cross sections are also presented for inclusive isolated-photon production as functions of the transverse energy and pseudorapidity of the photon. Higher-order theoretical calculations are compared to the results. (C) 2014 The Authors. Published by Elsevier B.V.

The reduced cross sections for e(+)p deep inelastic scattering have been measured with the ZEUS detector at HERA at three different center-of-mass 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 <= y <= 0.75, where y denotes the inelasticity and 5 <= Q(2) <= 110 GeV2. The proton structure functions F-2 and F-L were extracted from the measured cross sections.

The production of beauty and charm quarks in ep interactions has been studied with the ZEUS detector at HERA for exchanged four-momentum squared 5 < Q 2 < 1000 GeV2 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 decay-length significance of these vertices. Differential cross sections as a function of Q 2, Bjorken x, jet trans- verse energy and pseudorapidity were measured and compared with next-to-leading-order QCD calculations. The beauty and charm contributions to the proton structure functions were extracted from the double-differential cross section as a function of x and Q 2. The running beauty-quark mass, m b at the scale m b , was determined from a QCD fit at next-to-leading order to HERA data for the first time and found to be m b (m b ) = 4.07 ± 0.14 (fit) − 0.07 + 0.01 (mod.) − 0.00 + 0.05 (param.) − 0.05 + 0.08 (theo.) GeV.

The photoproduction of D ∗± mesons has been measured with the ZEUS detector at HERA at three different ep centre-of-mass 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 pseudo-rapidity, η D∗, in the ranges 1.9 < p T D ∗ < 20 GeV and |η D∗| < 1.6. The events were required to have a virtuality of the incoming photon, Q 2, of less than 1 GeV2. The dependence on \( \sqrt{s} \) was studied by normalising to the high-statistics measurement at \( \sqrt{s}=318 \) GeV. This led to the cancellation of a number of systematic effects both in data and theory. Predictions from next-to-leading-order QCD describe the \( \sqrt{s} \) dependence of the data well.

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 γ meas , contributing to the photon-jet final state. Cross sections are evaluated in the photon transverse-energy and pseudorapidity ranges 6 < E T γ < 15 GeV and −0.7 < η γ < 0.9, and for jet transverse-energy and pseudorapidity ranges 4 < E T jet < 35 GeV and −1.5 < η jet < 1.8, for an integrated luminosity of 374 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. Higher-order theoretical calculations are compared to the results.

The production of Z(0) bosons in the reaction ep -> eZ(0)p((*)), where p((*)) stands for a proton or a low-mass 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 pb(-1) of integrated luminosity. The Z(0) was measured in the hadronic decay mode. The elasticity of the events was ensured by a cut on eta(max) <3.0, where eta(ma)x is the maximum pseudorapidity of energy deposits in the calorimeter defined with respect to the proton beam direction. A signal was observed at the Z(0) mass. The cross section of the reaction ep -> eZ(0)p((*)) was measured to be sigma(ep -> eZ(0)p((*))) = 0.13 +/- 0.06(stat.) +/- 0.01(syst) pb, in agreement with the Standard Model prediction of 0.16 pb. Thfs is the first measurement of Z(0) production in ep collisions. (C) 2012 Elsevier B.V. All rights reserved.

The stages of development and the current status of the versatile “Spectrometer with a Vertex Detector” setup designed for physics experiments at the U-70 accelerator of the Institute for High Energy Physics (Protvino) is described. The main detectors of the setup are the vertex detector based on silicon microstrip detectors, the wide-aperture magnetic spectrometer based on multiwire proportional chambers, and the lead-glass hodoscope γ detector. In the setup, there is a fast two-level trigger system for selecting required particle interactions. The key characteristics of the setup systems are presented, and the physical results obtained on it are briefly listed.

The production of D *± 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 next-to-leading-order QCD calculations. The cross-sections are used to extract the charm contribution to the proton structure functions, expressed in terms of the reduced charm cross section, σ_red^cc . Theoretical calculations based on fits to inclusive HERA data are compared to the results.

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 D-meson production rates, the fraction of charged D mesons produced in a vector state, and the stangeness-suppression 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.

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 single-differential cross-sections $d\ensuremath{\sigma}/d{Q}^{2}$, $d\ensuremath{\sigma}/dx$ and $d\ensuremath{\sigma}/dy$ and the reduced cross section $\stackrel{\texttildelow{}}{\ensuremath{\sigma}}$ are measured in the kinematic region ${Q}^{2}>185\text{ }\text{ }{\mathrm{GeV}}^{2}$ and $y<0.9$, where ${Q}^{2}$ is the four-momentum 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 $135.5\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$ collected with the ZEUS detector in 2006 and 2007 at a center-of-mass energy of 318 GeV. The structure functions ${\stackrel{\texttildelow{}}{F}}_{3}$ and ${F}_{3}^{\ensuremath{\gamma}Z}$ are determined by combining the ${e}^{+}p$ results presented in this paper with previously published ${e}^{\ensuremath{-}}p$ 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.

The cross sections for inelastic photoproduction of J/psi and psi' mesons have been measured in ep collisions with the ZEUS detector at HERA, using an integrated luminosity of 38.0 pb-1. The events were required to have 0.1 < z < 0.9 and 50 < W < 180 GeV, where z is the fraction of the incident photon energy carried by the J/psi in the proton rest frame and W is the photon-proton centre-of-mass energy. The psi' to J/psi cross-section ratio was measured in the range 0.55 < z < 0.9. The J/psi data, for various ranges of transverse momentum, are compared to theoretical models incorporating colour-singlet and colour-octet matrix elements. Predictions of a next-to-leading-order colour-singlet model give a good description of the data, although there is a large normalisation uncertainty. The J/psi helicity distribution for z > 0.4 is compared to leading-order QCD predictions.