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    310 research outputs found

    NEUTRAL STRANGE PARTICLE-PRODUCTION IN DEEP-INELASTIC SCATTERING AT HERA RID B-9165-2008 RID C-5889-2009 RID A-4818-2008 RID C-1693-2008

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    This paper presents measurements of K-0 and Lambda production in neutral current, deep inelastic scattering of 26.7 GeV electrons and 820 GeV protons in the kinematic range 10 0.04. Average multiplicities for K-0 and Lambda production are determined for transverse momenta p(T) > 0.5 GeV and pseudorapidities \eta\ < 1.3. The multiplicities favour a stronger strange to light quark suppression in the fragmentation chain than found in e(+)e(-) experiments. The production properties of K-0's in events with and without a large rapidity gap with respect to the proton direction are compared. The ratio of neutral K-0's to charged particles per event in the measured kinematic range is, within the present statistics, the same in both samples
    Archivio della Ricerca - Università di Roma 3

    Measurement of D*+- production and the charm contribution to F(2) in deep inelastic scattering at HERA

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    The production of D*(+/-)(2010) mesons in deep inelastic scattering has been measured in the ZEUS detector at HERA using an integrated luminosity of 37 pb(-1). The decay channels D*(+) → D(0)pi(+) (+ c.c.), with D-0 → K(-)pi(+) or D-0 → K(- )pi(-)pi(+)pi(+), have been used to identify the D mesons. The e(+)p cross section for inclusive D*(+/-) production with 1 lt Q(2) lt 600 GeV2 and 0.02 lt y lt 0.7 is 8.31+/- 0.31(stat.)(+0.30)(-0.50) (syst.) nb in the kinematic region 1.5 lt pT(D*(+/-)) lt 15GeV and \eta(D*(+/-))\ lt 1.5. Differential cross sections are consistent with a next-to- leading-order perturbative-QCD calculation when using charm- fragmentation models which take into account the interaction of the charm quark with the proton remnant. The observed cross section is extrapolated to the full kinematic region in pr(D*(+/-)) and eta(D*(+/-)) in order to determine the charm contribution, F-2(c (c) over bar)(x,Q(2)), to the proton structllre function. The ratio F-2(c (c) over bar)/F-2 rises from similar or equal to 10% at Q(2) similar or equal to 1.8 GeV2 to similar or equal to 30% at Q(2) similar or equal to 130 GeV2 for x values in the rarlge 10(-4) to 10(-3)
    EDP Sciences OAI-PMH repository (1.2.0)
    DESY
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    ePubs: the open archive for STFC research publications
    The University of Manchester - Institutional Repository
    International Migration, Integration and Social Cohesion online publications
    Archivio istituzionale della ricerca - Università di Padova
    DESY Publication Database
    Crossref
    Oxford University Research Archive
    Andrews University
    Archivio della ricerca- Università di Roma La Sapienza

    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
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    International Migration, Integration and Social Cohesion online publications
    Archivio istituzionale della ricerca - Università di Padova
    DESY Publication Database
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    Oxford University Research Archive
    Andrews University
    Archivio istituzionale della ricerca - Alma Mater Studiorum Università di Bologna
    Archivio della Ricerca - Università di Salerno
    Archivio della ricerca- Università di Roma La Sapienza

    Study of the effective transverse momentum of partons in the proton using prompt photons in photoproduction at HERA

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    The photoproduction of prompt photons, together with an accompanying jet, has been measured with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb/sup -1/. A study of the effective transverse momentum, (k/sub T/), of partons in the proton, as modelled within the framework of the PYTHIA Monte Carlo, gives a value of (k/sub T/)=1.69+or-0.18/sub -0.20//sup +0.18/ GeV for the gamma p centre-of-mass energy range 134 lt W lt 251 GeV. This result is in agreement with the previously observed trend in hadron-hadron scattering for (k/sub T/) to rise with interaction energy
    Comparativ (E-Journal)
    Royal Holloway Research Online
    DESY
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    ePubs: the open archive for STFC research publications
    The University of Manchester - Institutional Repository
    International Migration, Integration and Social Cohesion online publications
    Archivio istituzionale della ricerca - Università di Padova
    DESY Publication Database
    Crossref
    Oxford University Research Archive
    Andrews University
    Archivio della ricerca- Università di Roma La Sapienza

    Measurement of charm fragmentation ratios and fractions in photoproduction at HERA

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    The production of D(*+), D(0), D(+), D(s)(+) and Lambda(+)(c) charm hadrons and their antiparticles in ep scattering at HERA was measured with the ZEUS detector using an integrated luminosity of 79 pb(-1). The measurement has been performed in the photoproduction regime with the exchanged-photon virtuality Q(2) 3.8 GeV and pseudorapidity vertical bar eta(D, Lambda(c))vertical bar D, Lambda(c)), were derived in the given kinematic range. The measured open-charm fragmentation fractions are consistent with previous results, although the measured f(c -> D(*+)) is smaller and f (c -> Lambda(+)(c)) is larger than those obtained in e(+)e(-) annihilations. These results generally support the hypothesis that fragmentation proceeds independently of the hard sub-process
    DESY Publication Database
    DESY
    Archivio istituzionale della ricerca - Alma Mater Studiorum Università di Bologna
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    DIAL UCLouvain
    Archivio della ricerca- Università di Roma La Sapienza
    Archivio istituzionale della ricerca - Università di Padova

    JET PRODUCTION IN HIGH Q(2) DEEP-INELASTIC EP SCATTERING AT HERA RID B-9165-2008 RID C-5889-2009 RID A-4818-2008 RID C-1693-2008

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    Two-jet production in deep-inelastic electron-proton scattering has been studied for 160 < Q(2) < 1280 GeV2 0.01 < x < 0.1 and 0.04 < y < 0.95 with the ZEUS detector at HERA. The kinematic properties of the jets and the jet production rates are presented. The partonic scaling variables of the two-jet system and the rate of two-jet production are compared to perturbative next-to-leading order QCD calculations
    Archivio della Ricerca - Università di Roma 3

    MEASUREMENT OF THE DIFFRACTIVE STRUCTURE-FUNCTION IN DEEP-INELASTIC SCATTERING AT HERA RID B-9165-2008 RID C-5889-2009 RID A-4818-2008 RID C-1693-2008

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    This paper presents an analysis of the inclusive properties of diffractive deep inelastic scattering events produced in ep interactions at HERA. The events are characterised by a rapidity gap between the outgoing proton system and the remaining hadronic system. Inclusive distributions are presented and compared with Monte Carlo models for diffractive processes. The data are consistent with models where the pomeron structure function has a hard and a soft contribution. The diffractive structure function is measured as a function of x(p), the momentum fraction lost by the proton, of beta, the momentum fraction of the struck quark with respect to x(p), and of Q(2) in the range 6.3 10(-4) < x(p) < 10(-2), 0.1 < .beta < 0.8 and 8 < Q(2) < 100 GeV2. The x(p) dependence is consistent with the form (1/x(p))(alpha) where alpha = 1.30 +/- 0.08 (stat)(-0.14)(+0.08) (sys) in all bins of beta and Q(2). In the measured Q(2) range, the diffractive structure function approximately scales with Q(2) at fixed beta. In an Ingelman-Schlein type model where commonly used pomeron flux factor normalisations are assumed, it is found that the quarks within the pomeron do not saturate the momentum sum rule
    Archivio della Ricerca - Università di Roma 3

    MEASUREMENT OF THE PROTON STRUCTURE-FUNCTION F2 FROM THE 1993 HERA DATA RID B-9165-2008 RID C-5889-2009 RID A-4818-2008 RID C-1693-2008

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    The ZEUS detector has been used to measure the proton structure function F-2. During 1993 HERA collided 26.7 GeV electrons on 820 GeV protons. The data sample corresponds to an integrated luminosity of 0.54 pb(-1), representing a twenty fold increase in statistics compared to that of 1992. Results are presented for 7 < Q(2) < 10(4) GeV2 and x values as low as 3 x 10(-4). The rapid rise in F-2 as x decreases observed previously is now studied in greater detail and persists for Q(2) values up to 500 GeV2
    Archivio della Ricerca - Università di Roma 3

    A SEARCH FOR EXCITED FERMIONS IN ELECTRON-PROTON COLLISIONS AT HERA RID B-9165-2008 RID C-5889-2009 RID A-4818-2008 RID C-1693-2008

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    A search for excited states of the standard model fermions was performed using the ZEUS detector at the HERA electron-proton collider, operating at a centre of mass energy of 296 GeV. In a sample corresponding to an integrated luminosity of 0.55 pb(-1), no evidence was found for any resonant state decaying into final states composed of a fermion and a gauge boson. Limits on the coupling strength times branching ratio of excited fermions are presented for masses between 50 GeV and 250 GeV, extending previous search regions significantly
    Archivio della Ricerca - Università di Roma 3

    Measurement of K-S(0), Lambda and (Lambda)over-bar production at HERA

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    The production of the neutral strange hadrons K0S, Λ and Λ has been measured in ep collisions at HERA using the ZEUS detector. Cross sections, baryon-to-meson ratios, relative yields of strange and charged light hadrons, Λ (Λ) asymmetry and polarization have been measured in three kinematic regions: Q2 > 25 GeV2; 5 < Q2 < 25 GeV2; and in photoproduction (Q 2 0). In photoproduction the presence of two hadronic jets, each with at least 5 GeV transverse energy, was required. The measurements agree in general with Monte Carlo models and are consistent with measurements made at e+e- colliders, except for an enhancement of baryon relative to meson production in photoproduction. © Springer-Verlag / Società Italiana di Fisica 2007
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    Archivio istituzionale della ricerca - Università di Padova
    DESY Publication Database
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    Oxford University Research Archive
    Andrews University
    Archivio istituzionale della ricerca - Alma Mater Studiorum Università di Bologna
    Archivio della Ricerca - Università di Salerno
    DIAL UCLouvain
    Archivio della ricerca- Università di Roma La Sapienza
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