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 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.

Inclusive production cross sections of pi(+/-), K-+/- and p/(p) over bar per hadronic e(+)e(-) annihilation event are measured at a center-of-mass energy of 10.54 GeV, using a relatively small sample of very high quality data from the BABAR experiment at the PEP-II B-factory at the SLAC National Accelerator Laboratory. The drift chamber and Cherenkov detector provide clean samples of identified pi(+/-), K-+/-, and p/(p) over bar over a wide range of momenta. Since the center-of-mass energy is below the threshold to produce a B (B) over bar pair, with B a bottom-quark meson, these data represent a pure e(+)e(-) -> q (q) over bar sample with four quark flavors, and are used to test QCD predictions and hadronization models. Combined with measurements at other energies, in particular at the Z(0) resonance, they also provide precise constraints on the scaling properties of the hadronization process over a wide energy range.

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.

Three-jet production in deep inelastic ep scattering and photoproduction was investigated with the ZEUS detector at HERA using an integrated luminosity of 127 pb-1. Measurements of differential cross sections are presented as functions of angular correlations between the three jets in the final state and the proton-beam direction. These correlations provide a stringent test of perturbative QCD and show sensitivity to the contributions from different colour configurations. Fixed-order perturbative QCD calculations assuming the values of the colour factors C_F, C_A and T_F 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 colour configurations as predicted by SU(3) and disfavour other symmetry groups, such as SU(N) in the limit of large N.

The exclusive electroproduction of two pions in the mass range 0.4<M ππ <2.5 GeV has been studied with the ZEUS detector at HERA using an integrated luminosity of 82 pb−1. The analysis was carried out in the kinematic range of 2<Q 2<80 GeV2, 32<W<180 GeV and |t|<0.6 GeV2, 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 two-pion invariant-mass distribution is interpreted in terms of the pion electromagnetic form factor, |F(M ππ )|, assuming that the studied mass range includes the contributions of the ρ, ρ′ and ρ′′ vector-meson states. The masses and widths of the resonances were obtained and the Q 2 dependence of the cross-section ratios σ(ρ′→ππ)/σ(ρ) and σ(ρ′′→ππ)/σ(ρ) was extracted. The pion form factor obtained in the present analysis is compared to that obtained in e + e −→π + π −.

A search for first-generation leptoquarks was performed in electron-proton and positron-proton collisions recorded with the ZEUS detector at HERA in 2003-2007 using an integrated luminosity of 366 pb^-1. Final states with an electron and jets or with missing transverse momentum and jets were analysed, 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 pb^-1. Limits on the Yukawa coupling, lambda, of leptoquarks were set as a function of the leptoquark mass for different leptoquark types within the Buchmueller-Rueckl-Wyler model. Leptoquarks with a coupling lambda=0.3 are excluded for masses up to 699 GeV.

Inclusive-jet cross sections have been measured in the reaction ep→e+jet+X for photon virtuality Q2<1 GeV2 and γp centre-of-mass energies in the region 14217 GeV and −1<ηjet<2.5. In addition, measurements of double-differential inclusive-jet cross sections are presented as functions of ETjet in different regions of ηjet. Next-to-leading-order QCD calculations give a good description of the measurements, except for jets with low ETjet and high ηjet. The influence of non-perturbative 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(αs2) terms. Values of αs(MZ) were extracted from the measurements and the energy-scale dependence of the coupling was determined. The value of αs(MZ) extracted from the measurements based on the kT jet algorithm is αs(MZ)=0.1206−0.0022+0.0023(exp.)−0.0035+0.0042(th.); the results from the anti-kT and SIScone algorithms are compatible with this value and have a similar precision.

The production of isolated high-energy photons accompanied by jets has been measured in deep inelastic ep scattering with the ZEUS detector at HERA, using an integrated luminosity of 326 pb(-1). Measurements were made for exchanged photon virtualities Q(2), in the range 10 to 350 GeV2. The photons were measured in the transverse-energy and pseudorapidity ranges 4 < E-T(gamma) < 15 GeV and -0.7 < eta(gamma) < 0.9, and the jets were measured in the transverse-energy and pseudorapidity ranges 2.5 < E-T(jet) < 35 GeV and -15< eta(jet) < 1.8. 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%. (c) 2012 Elsevier B.V. All rights reserved.

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. Leading-logarithm parton-shower Monte Carlo calculations interfaced to the Lund string fragmentation model describe the data reasonably well in the whole range measured. Next-to-leading-order 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, anti-quarks and gluons yielding $ K_{\text{S}}^0 $ and $ \Lambda /\bar{\Lambda } $ strange hadrons.

The exclusive electroproduction of two pions in the mass range 0.4 < Mππ < 2.5 GeV has been studied with the ZEUS detector at HERA using an integrated luminosity of 82 pb−1. 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 photon-proton centre-of-mass energy and t is the squared four-momentum transfer at the proton vertex. The Eur. Phys. J. C (2012) 72:1869 Page 3 of 12 two-pion invariant-mass distribution is interpreted in terms of the pion electromagnetic form factor, |F(Mππ)|, assuming that the studied mass range includes the contributions of the ρ, ρ′ and ρ′′ vector-meson states. The masses and widths of the resonances were obtained and the Q2 dependence of the cross-section ratios σ(ρ′ → ππ)/σ(ρ) and σ(ρ′′ → ππ)/σ(ρ) was extracted. The pion form factor obtained in the present analysis is compared to that obtained in e+e− → π+π−. a e-mail: levy@alzt.tau.ac.il ASupported by the US Department of Energy BSupported by the Italian National Institute for Nuclear Physics (INFN) CSupported by the German Federal Ministry for Education and Research (BMBF), under contract No. 05 H09PDF DSupported by the Science and Technology Facilities Council, UK ESupported by an FRGS grant from the Malaysian government FSupported by the US National Science Foundation. Any opinion, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation GSupported by the Polish Ministry of Science and Higher Education as a scientific project No. DPN/N188/DESY/2009 HSupported by the Polish Ministry of Science and Higher Education and its grants for Scientific Research ISupported by the German Federal Ministry for Education and Research (BMBF), under contract No. 05h09GUF, and the SFB 676 of the Deutsche Forschungsgemeinschaft (DFG) JSupported by the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) and its grants for Scientific Research KSupported by the Korean Ministry of Education and Korea Science and Engineering Foundation LSupported by FNRS and its associated funds (IISN and FRIA) and by an Inter-University Attraction Poles Programme subsidised by the Belgian Federal Science Policy Office MSupported by the Spanish Ministry of Education and Science through funds provided by CICYT NSupported by the Natural Sciences and Engineering Research Council of Canada (NSERC) OPartially supported by the German Federal Ministry for Education and Research (BMBF) PSupported by RF Presidential grant N 4142.2010.2 for Leading Scientific Schools, by the Russian Ministry of Education and Science through its grant for Scientific Research on High Energy Physics and under contract No.02.740.11.0244 QSupported by the Netherlands Foundation for Research on Matter (FOM) RSupported by the Israel Science Foundation bNow at University of Salerno, Italy cNow at Queen Mary University of London, United Kingdom dAlso funded by Max Planck Institute for Physics, Munich, Germany eAlso Senior Alexander von Humboldt Research Fellow at Hamburg University, Institute of Experimental Physics, Hamburg, Germany

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. Leading-logarithm parton-shower Monte Carlo calculations interfaced to the Lund string fragmentation model describe the data reasonably well in the whole range measured. Next-to-leading-order 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, anti-quarks and gluons yielding \( K_{\text{S}}^0 \) and \( \Lambda /\bar{\Lambda } \) strange hadrons.

The EUDET-project was launched to create an infrastructure for developing and testing new and advanced detector technologies to be used at a future linear collider. The aim was to make possible experimentation and analysis of data for institutes, which otherwise could not be realized due to lack of resources. The infrastructure comprised an analysis and software network, and instrumentation infrastructures for tracking detectors as well as for calorimetry.

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 centre-of-mass energy √ s = 318 GeV where leading protons are detected by dedicated spectrometers. Correlations of systematic uncertainties are taken into account, resulting in an

Scaled momentum distributions for the strange hadrons K 0 S and Λ / ¯Λ were measured in deep inelastic ep scattering with the ZEUS detector at HERA using an integrated luminosity of 330 pb − 1 in the kinematic region 10 < Q 2 < 40000 GeV 2 and 0 . 001 < x < 0 . 75 . Predictions based on different approaches to fragmentation were compared to the measurements. Next-to-leading-order QCD calculations based on fragmentation functions, FFs, extracted from e + e − data alone, fail to describe the measurements. The measurements presented in this paper have the potential to further constrain the fragmentation functions of quarks, anti-quarks and gluons yielding K 0 S and Λ / ¯Λ strange hadrons.