173 research outputs found

    Search for a narrow charmed baryonic state decaying to D*(+/-)p(-/+) in ep collisions at HERA

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    A resonance search has been made in the D*±p∓ invariant-mass spectrum with the ZEUS detector at HERA using an integrated luminosity of 126 pb-1. The decay channels D*+ -→ D0πs+ → (K -π+)πs+ and D*+ → D0πs+ → (K-π+π+π-) πs+ (and the corresponding antiparticle decays) were used to identify D*± mesons. No resonance structure was observed in the D*± p∓ mass spectrum from more than 60 000 reconstructed D*± mesons. The results are not compatible with a report of the H1 Collaboration of a charmed pentaquark, Θc0. © Springer-Verlag / Società Italiana di Fisica 2004

    Measurement of charmed hadron production in e±p deep inelastic scattering with the ZEUS detector

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    Charmed hadron production has been studied in 225 pb-1 of data collected with the ZEUS detector in the HERA-II runnning period. Studies were made in the D* → D0π → Kππ decay channel to determine the potential for the microvertex detector to improve charm signals. Integrated cross sections were measured for the decays D0 → K0sπ⁺ π⁻, D± → K0s π±, D±_s → K0s K± and Lambda±_c → Lambda0π± in the kinematic region 5 1.0 GeV. Differential cross sections as a function of Q², x, pT(D) and pseudorapidity(D) were measured for the D0, D±, and D_s± channels. The measurements were compared to next-to-leading order (NLO) QCD calculations, and good agreement found for all variables in all channels over the measured kinematic region. The strangeness-suppression factor, gamma_s = D_s±/(D± + D0), was measured and found to be in good agreement with values previously measured at HERA and elsewhere, and with the DJANGOH and RAPGAP Monte Carlo. The ratio of charmed baryons to mesons, Lambda_c±/(D± + D0), was measured and also found to be in good agreement with Monte Carlo

    Measurement of charmed hadron production in e±p deep inelastic scattering with the ZEUS detector

    No full text
    Charmed hadron production has been studied in 225 pb-1 of data collected with the ZEUS detector in the HERA-II runnning period. Studies were made in the D* → D0π → Kππ decay channel to determine the potential for the microvertex detector to improve charm signals. Integrated cross sections were measured for the decays D0 → K0sπ⁺ π⁻, D± → K0s π±, D±_s → K0s K± and Lambda±_c → Lambda0π± in the kinematic region 50 cross section was additionally measured down to pT(D0) > 1.0 GeV. Differential cross sections as a function of Q², x, pT(D) and pseudorapidity(D) were measured for the D0, D±, and D_s± channels. The measurements were compared to next-to-leading order (NLO) QCD calculations, and good agreement found for all variables in all channels over the measured kinematic region. The strangeness-suppression factor, gamma_s = D_s±/(D± + D0), was measured and found to be in good agreement with values previously measured at HERA and elsewhere, and with the DJANGOH and RAPGAP Monte Carlo. The ratio of charmed baryons to mesons, Lambda_c±/(D± + D0), was measured and also found to be in good agreement with Monte Carlo.Some figures have been removed from this version of the thesis for copyright reasons

    Measurement of D-*+/- meson production in e(+/-)p scattering at low Q(2)

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    The production of D* ± (2010) mesons in e± p scattering in the range of exchanged photon virtuality 0.05 < Q2 < 0.7   GeV2 has been measured with the ZEUS detector at HERA using an integrated luminosity of 82 pb-1. The decay channels D* + → D0 π+ with D0 → K- π+ and corresponding antiparticle decay were used to identify D* mesons and the ZEUS beampipe calorimeter was used to identify the scattered electron. Differential D* cross sections as functions of Q2, inelasticity, y, transverse momentum of the D* meson, pT (D*), and pseudorapidity of the D* meson, η (D*), have been measured in the kinematic region 0.02 < y < 0.85, 1.5 < pT (D*) < 9.0   GeV and | η (D*) | < 1.5. The measured differential cross sections are in agreement with two different NLO QCD calculations. The cross sections are also compared to previous ZEUS measurements in the photoproduction and DIS regimes. © 2007 Elsevier B.V. All rights reserved

    Measurement of the charm fragmentation function in D* photoproduction at HERA

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    The charm fragmentation function has been measured in D* photoproduction with the ZEUS detector at HERA using an integrated luminosity of 120 pb-1. The fragmentation function is measured versus z = (E +p||)D* /2Ejet, where E is the energy of the D * meson and p|| is the longitudinal momentum of the D * meson relative to the axis of the associated jet of energy Ejet. Jets were reconstructed using the kT clustering algorithm and required to have transverse energy larger than 9GeV. The D* meson associated with the jet was required to have a transverse momentum larger than 2GeV. The measured function is compared to different fragmentation models incorporated in leading-logarithm Monte Carlo simulations and in a next-to-leading-order QCD calculation. The free parameters in each fragmentation model are fitted to the data. The extracted parameters and the function itself are compared to measurements from e+e-experiments. © SISSA 2009

    Measurement of D ± and D 0 production in deep inelastic scattering using a lifetime tag at HERA

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    The production of D &lt;sup&gt;±&lt;/sup&gt;- and D &lt;sup&gt;0&lt;/sup&gt;-mesons has been measured with the ZEUS detector at HERA using an integrated luminosity of 133.6 pb&lt;sup&gt;−1&lt;/sup&gt;. The measurements cover the kinematic range 5&#60;Q &lt;sup&gt;2&lt;/sup&gt;&#60;1000 GeV&lt;sup&gt;2&lt;/sup&gt;, 0.02&#60;y&#60;0.7, 1.5&#60;&lt;sub&gt;p&lt;/sub&gt;&lt;sub&gt;T&lt;/sub&gt;&lt;sup&gt;D&lt;/sup&gt; &#60;15 GeV and |η &lt;sup&gt;D&lt;/sup&gt; |&#60;1.6. Combinatorial background to the D-meson signals is reduced by using the ZEUS microvertex detector to reconstruct displaced secondary vertices. Production cross sections are compared with the predictions of next-to-leading-order QCD, which is found to describe the data well. Measurements are extrapolated to the full kinematic phase space in order to obtain the open-charm contribution, F&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;cc&lt;/sup&gt; , to the proton structure function, F &lt;sub&gt;2&lt;/sub&gt;

    Multijet cross sections in charged current e(+/-)p scattering at HERA

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    Jet cross sections were measured in charged-current deep inelastic e±p scattering at high boson virtualities Q2 with the ZEUS detector at HERA II using an integrated luminosity of 0.36fb-1. Differential cross sections are presented for inclusive-jet production as functions of Q2, Bjorken x and the jet transverse energy and pseudorapidity. The dijet invariant mass cross section is also presented. Observation of three- and four-jet events in charged-current e±p processes is reported for the first time. The predictions of next-to-leading-order (NLO) QCD calculations are compared to the measurements. The measured inclusive-jet cross sections are well described in shape and normalization by the NLO predictions. The data have the potential to constrain the u and d valence-quark distributions in the proton if included as input to global fits. © 2008 The American Physical Society

    Diffractive photoproduction of D*(+/-) (2010) at HERA

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    Diffractive photoproduction of D*±(2010) mesons was measured with the ZEUS detector at the ep collider HERA, using an integrated luminosity of 78.6 pb-1. The D* mesons were reconstructed in the kinematic range: transverse momentum pT(D*) > 1.9 GeV and pseudorapidity |η(D*)|<1.6, using the decay D*+→D0π+s followed by D0→K-π+(+c.c.). Diffractive events were identified by a large gap in pseudorapidity between the produced hadronic state and the outgoing proton. Cross sections are reported for photon-proton centre-of-mass energies in the range 130 < W < 300 GeV and for photon virtualities Q2 < 1 GeV2, in two ranges of the Pomeron fractional momentum xIP<0.035 and xIP<0.01. The relative contribution of diffractive events to the inclusive D*±(2010) photoproduction cross section is about 6%. The data are in agreement with perturbative QCD calculations based on various parameterisations of diffractive parton distribution functions. The results are consistent with diffractive QCD factorisation. © Springer-Verlag Berlin Heidelberg 2007

    Measurement of open beauty production at HERA in the D* mu final state

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    The production of beauty quarks with a D and a muon in the final state has been measured with the ZEUS detector at HERA using an integrated luminosity of 114 pb&lt;sup&gt;-1&lt;/sup&gt;. Low transverse-momentum thresholds for the muon and D&lt;sup&gt;*&lt;/sup&gt; meson allow for a measurement of beauty production closer to the production threshold than previous measurements. The beauty signal was extracted using the charge correlations and angular distributions of the muon with respect to the D* meson. Cross sections for photoproduction and deep inelastic scattering are somewhat higher than, but compatible with, next-to-leading-order QCD predictions, and compatible with other measurements

    Measurement of charged current deep inelastic scattering cross sections with a longitudinally polarised electron beam at HERA

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    Measurements of the neutral current cross sections for deep inelastic scattering in e - p collisions at HERA with a longitudinally polarised electron beam are presented. The single-differential cross-sections d σ/dQ 2, d σ/dx and d σ/dy and the double-differential cross sections in Q 2 and x are measured in the kinematic region y185∈GeV 2 for both positively and negatively polarised electron beams and for each polarisation state separately. The measurements are based on an integrated luminosity of 169.9∈pb -1 taken with the ZEUS detector in 2005 and 2006 at a centre-of-mass energy of 318∈GeV. The structure functions F3 and xF 3γ Z are determined by combining the e - p results presented in this paper with previously measured e + p neutral current data. The asymmetry parameter A - is used to demonstrate the parity violating effects of electroweak interactions at large spacelike photon virtuality. The measurements agree well with the predictions of the Standard Model. © 2009 Springer-Verlag / Società Italiana di Fisica
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