Photoproduction of beauty quarks in events with two jets and an electron associated with one of the jets has been studied with the ZEUS detector at HERA using an integrated luminosity of 120pb^-1. The fractions of events containing b quarks, and also of events containing c quarks, were extracted from a likelihood fit using variables sensitive to electron identification as well as to semileptonic decays. Total and differential cross sections for beauty and charm production were measured and compared with next-to-leading-order QCD calculations and Monte Carlo models.
Total cross sections for electrons from beauty and charm quarks.
Differential electron cross sections as a function of PT and ETARAP from beauty and charm quarks.
Differential electron cross sections as a function of PT and ETARAP from beauty and charm quarks.
The photoproduction of beauty quarks in events with two jets and a muon has been measured with the ZEUS detector at HERA using an integrated luminosity of 110 pb$^{- 1}$. The fraction of jets containing b quarks was extracted from the transverse momentum distribution of the muon relative to the closest jet. Differential cross sections for beauty production as a function of the transverse momentum and pseudorapidity of the muon, of the associated jet and of $x_{\gamma}^{jets}$, the fraction of the photon's momentum participating in the hard process, are compared with MC models and QCD predictions made at next-to-leading order. The latter give a good description of the data.
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Charged particles ($h^\pm$) and \kz mesons have been studied in photoproduced events containing at least one jet of $E_T > 8$ GeV in a pseudorapidity interval (--0.5, 0.5) in the ZEUS laboratory frame. Distributions are presented in terms of transverse momentum, pseudorapidity and distance of the particle from the axis of a jet. The properties of \hpm within the jet are described well using the standard settings of PYTHIA, but the use of the multiparton interaction option improves the description outside the jets. A reasonable overall description of the \kz behaviour is possible with PYTHIA using a reduced value of the strangeness suppression parameter. The numbers of $h^\pm$ and \kz within a jet as defined above are measured to be $3.25\pm0.02\pm0.28$ and $0.431\pm0.013\pm0.088$ respectively. Fragmentation functions are presented for $h^\pm$ and \kz in photoproduced jets; agreement is found with calculations of Binnewies et al. and, at higher momenta, with $p\bar p$ scattering and with standard PYTHIA. Fragmentation functions in direct photoproduced events are extracted, and at higher momenta give good agreement with data from related processes in $e^+e^-$ annihilation and deep inelastic $ep$ scattering.
Corrected multiplicities of charged particles and neutral K0 mesons per photoproduced jet.
Corrected distribution of charged particles per jet in events containing a hadron jet.
Corrected distribution of charged particles per jet in events containing a hadron jet.
This paper presents measurements of D^{*\pm} production in deep inelastic scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The data have been taken with the ZEUS detector at HERA. The decay channel $D^{*+}\to (D^0 \to K^- \pi^+) \pi^+ $ (+ c.c.) has been used in the study. The $e^+p$ cross section for inclusive D^{*\pm} production with $5<Q^2<100 GeV^2$ and $y<0.7$ is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region {$1.3<p_T(D^{*\pm})<9.0$ GeV and $| \eta(D^{*\pm}) |<1.5$}. Differential cross sections as functions of p_T(D^{*\pm}), $\eta(D^{*\pm}), W$ and $Q^2$ are compared with next-to-leading order QCD calculations based on the photon-gluon fusion production mechanism. After an extrapolation of the cross section to the full kinematic region in p_T(D^{*\pm}) and $\eta$(D^{*\pm}), the charm contribution $F_2^{c\bar{c}}(x,Q^2)$ to the proton structure function is determined for Bjorken $x$ between 2 $\cdot$ 10$^{-4}$ and 5 $\cdot$ 10$^{-3}$.
No description provided.
Integrated charm cross sections in two Q**2 regions.
Distribution of the fractional momentum of the D* in the gamma*-p system.
Deep inelastic scattering and its diffractive component, $ep \to e^{\prime}\gamma^* p \to e^{\prime}XN$, have been studied at HERA with the ZEUS detector using an integrated luminosity of 52.4 pb$^{-1}$. The $M_X$ method has been used to extract the diffractive contribution. A wide range in the centre-of-mass energy $W$ (37 -- 245 GeV), photon virtuality $Q^2$ (20 -- 450 GeV$^2$) and mass $M_X$ (0.28 -- 35 GeV) is covered. The diffractive cross section for $2 < M_X < 15$ GeV rises strongly with $W$, the rise becoming steeper as $Q^2$ increases. The data are also presented in terms of the diffractive structure function, $F^{\rm D(3)}_2$, of the proton. For fixed $Q^2$ and fixed $M_X$, $\xpom F^{\rm D(3)}_2$ shows a strong rise as $\xpom \to 0$, where $\xpom$ is the fraction of the proton momentum carried by the Pomeron. For Bjorken-$x < 1 \cdot 10^{-3}$, $\xpom F^{\rm D(3)}_2$ shows positive $\log Q^2$ scaling violations, while for $x \ge 5 \cdot 10^{-3}$ negative scaling violations are observed. The diffractive structure function is compatible with being leading twist. The data show that Regge factorisation is broken.
Proton structure function F2 at Q**2 = 25 GeV**2.
Proton structure function F2 at Q**2 = 35 GeV**2.
Proton structure function F2 at Q**2 = 45 GeV**2.
The dissociation of virtual photons, $\gamma^{\star} p \to X p$, in events with a large rapidity gap between $X$ and the outgoing proton, as well as in events in which the leading proton was directly measured, has been studied with the ZEUS detector at HERA. The data cover photon virtualities $Q^2>2$ GeV$^2$ and $\gamma^{\star} p$ centre-of-mass energies $40<W<240$ GeV, with $M_X>2$ GeV, where $M_X$ is the mass of the hadronic final state, $X$. Leading protons were detected in the ZEUS leading proton spectrometer. The cross section is presented as a function of $t$, the squared four-momentum transfer at the proton vertex and $\Phi$, the azimuthal angle between the positron scattering plane and the proton scattering plane. It is also shown as a function of $Q^2$ and $\xpom$, the fraction of the proton's momentum carried by the diffractive exchange, as well as $\beta$, the Bjorken variable defined with respect to the diffractive exchange.
The differential cross section DSIG/DT for the LRG and the LPS data samples.
The fitted exponential slope of the T distribution as a function of X(NAME=POMERON).
The fitted exponential slope of the T distribution as a function of X(NAME=POMERON).
The virtual photon absorption cross section differences [sigma_1/2-sigma_3/2] for the proton and neutron have been determined from measurements of polarised cross section asymmetries in deep inelastic scattering of 27.5 GeV longitudinally polarised positrons from polarised 1H and 3He internal gas targets. The data were collected in the region above the nucleon resonances in the kinematic range nu < 23.5 GeV and 0.8 GeV**2 < Q**2 < 12 GeV**2. For the proton the contribution to the generalised Gerasimov-Drell-Hearn integral was found to be substantial and must be included for an accurate determination of the full integral. Furthermore the data are consistent with a QCD next-to-leading order fit based on previous deep inelastic scattering data. Therefore higher twist effects do not appear significant.
Gerasimov-Drell-Hearn sum rule for proton as a function of Q2.
Gerasimov-Drell-Hearn sum rule for neutron as a function of Q2 (integral spans from Q2/2M to infinity instead of zero to infinity, see paper).
Cross section difference for the proton data. Statistical errors only.
Differential dijet cross sections have been measured with the ZEUS detector for photoproduction events in which the hadronic final state containing the jets is separated with respect to the outgoing proton direction by a large rapidity gap. The cross section has been measured as a function of the fraction of the photon (x_gamma^OBS) and pomeron (beta^OBS) momentum participating in the production of the dijet system. The observed x_gamma^OBS dependence shows evidence for the presence of a resolved- as well as a direct-photon component. The measured cross section d(sigma)/d(beta^OBS) increases as beta^OBS increases indicating that there is a sizeable contribution to dijet production from those events in which a large fraction of the pomeron momentum participates in the hard scattering. These cross sections and the ZEUS measurements of the diffractive structure function can be described by calculations based on parton densities in the pomeron which evolve according to the QCD evolution equations and include a substantial hard momentum component of gluons in the pomeron.
Differential cross section as a function of rapidity of the two highest Et jets in event.
Differential cross section as a function of transverse energy Et of the tw o highest Et jets in event.
Differential cross section as a function of invariant mass of the GAMMA P system.
Diffractive photoproduction of dijets was measured with the ZEUS detector at the ep collider HERA using an integrated luminosity of 77.2 pb-1. The measurements were made in the kinematic range Q^2 < 1 GeV^2, 0.20 < y < 0.85 and x_pom < 0.025, where Q^2 is the photon virtuality, y is the inelasticity and x_pom is the fraction of the proton momentum taken by the diffractive exchange. The two jets with the highest transverse energy, E_T^jet, were required to satisfy E_T^jet > 7.5 and 6.5 GeV, respectively, and to lie in the pseudorapidity range -1.5 < eta^jet < 1.5. Differential cross sections were compared to perturbative QCD calculations using available parameterisations of diffractive parton distributions of the proton.
Differential cross section DSIG/DY for diffractive photoproduction of dijets as a function of Y.
Differential cross section DSIG/DM(P=5_6_7) for diffractive photoproduction of dijets as a function of M(P=5_6_7).
Differential cross section DSIG/DX(NAME=POMERON) for diffractive photoproduction of dijets as a function of X(NAME=POMERON).
Dijet cross sections are presented using photoproduction data obtained with the ZEUS detector during 1994. These measurements represent an extension of previous results, as the higher statistics allow cross sections to be measured at higher jet transverse energy (ETJ). Jets are identified in the hadronic final state using three different algorithms, and the cross sections compared to complete next-to-leading order QCD calculations. Agreement with these calculations is seen for the pseudorapidity dependence of the direct photon events with ETJ > 6 GeV and of the resolved photon events with ETJ > 11 GeV. Calculated cross sections for resolved photon processes with 6 GeV < ETJ < 11 GeV lie below the data.
Dijet cross section using the KTCLUS jet alogrithm with a minimum ET for each jet of 6 GeV and a requirement on X(NAME=GAMMA_OBS) to be 0.0 TO 1.0. The second DSYS errors are the correlated uncertainties.
Dijet cross section using the KTCLUS jet alogrithm with a minimum ET for each jet of 8 GeV and a requirement on X(NAME=GAMMA_OBS) to be 0.0 TO 1.0. The second DSYS errors are the correlated uncertainties.
Dijet cross section using the KTCLUS jet alogrithm with a minimum ET for each jet of 11 GeV and a requirement on X(NAME=GAMMA_OBS) to be 0.0 TO 1.0. The second DSYS errors are the correlated uncertainties.
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