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    16 research outputs found

    A ring system detected around the Centaur (10199) Chariklo

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    Hitherto, rings have been found exclusively around the four giant planets in the Solar System1. Rings are natural laboratories in which to study dynamical processes analogous to those that take place during the formation of planetary systems and galaxies. Their presence also tells us about the origin and evolution of the body they encircle. Here we report observations of a multichord stellar occultation that revealed the presence of a ring system around (10199) Chariklo, which is a Centaur—that is, one of a class of small objects orbiting primarily between Jupiter and Neptune—with an equivalent radius of 124± 9 kilometres (ref. 2). There are two dense rings, with respective widths of about 7 and 3 kilometres, optical depths of 0.4 and 0.06, and orbital radii of 391 and 405 kilometres. The present orientation of the ring is consistent with an edge-on geometry in 2008, which provides a simple explanation for the dimming3 of the Chariklo system between 1997 and 2008, and for the gradual disappearance of ice and other absorption features in its spectrum over the same period4,5. This implies that the rings are partly composed of water ice. They may be the remnants of a debris disk, possibly confined by embedded, kilometre-sized satellites.Peer reviewe
    Repositório Institucional UNESP
    LAReferencia - Red Federada de Repositorios Institucionales de Publicaciones Científicas Latinoamericanas
    HAL Descartes
    Carolina Digital Repository
    Open Repository and Bibliography - Liège
    Acervo Digital da Universidade Estadual Paulista
    HAL-CEA
    MPG.PuRe
    Hal-Diderot
    Crossref
    CONICET Digital
    Open Research Online
    Copenhagen University Research Information System
    HAL-INSU
    HAL-OBSPM
    University of St Andrews Research Portal
    HAL
    University of St. Andrews - Pure
    St Andrews Research Repository

    Jet shapes at HERA

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    The shape of jets produced in quasi-real photon-proton interactions and deep inelastic positron-proton scattering (DIS) at high Q(2) (Q(2) > 100 GeV2) has been measured with the ZEUS detector at HERA. Jets with transverse energies E-T(jet) > 14 GeV and pseudorapidities (eta(jet)) in the range -1 collisions, and are similar to those in e(+)e(-) interactions
    Archivio della Ricerca - Università di Roma 3

    Recent photoproduction results from ZEUS

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    Recent results for inclusive jet cross sections, dijet cross sections and dijet angular distributions are compared with NLO perturbative QCD calculations. The observation of isolated high PT photons (prompt photons) is also reported
    Archivio della Ricerca - Università di Roma 3

    Event shape analysis of multihadronic final states in deep inelastic rapidity gap events at HERA

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    A global event shape analysis of the multihadronic final states observed in deep inelastic scattering (DIS) with a large forward rapidity gap (LRG) is performed in the range Q(2) greater than or equal to 5 GeV2, 160 GeV less than or equal to W less than or equal to 250 GeV and eta(max) less than or equal to 1.8. Particular emphasis is paid to the dependence of these variables, measured in the gamma*-pomeron rest frame, upon M-X, the mass of the hadronic final state. With increasing M-X the multihadronic final states become planar. The broadening effects exhibited by the data can be described by including a gluon density in models where the pomeron has a partonic structure or alternatively by considering a direct coupling of the pomeron to quark and gluon pairs
    Archivio della Ricerca - Università di Roma 3

    High Q(2) events in ep collisions

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    Using the ZEUS detector at HERA, we have studied the reaction e(+) p --> e(+) X for Q(2) > 5000 GeV2 with a 20.1 pb(-1) data sample collected during the years 1994 to 1996. For Q(2) below 15000 GeV2, the data are in good agreement with Standard Model expectations. For Q(2) > 35000 GeV2, two events are observed while 0.145 +/- 0.013 events are expected. For x > 0.55 and y > 0.25, four events are observed where 0.91 +/- 0.08 events are expected. The observed excess above Standard Model expectations is particularly interesting because it occurs in a previously unexplored kinematic region
    Archivio della Ricerca - Università di Roma 3

    F-2(D(3)) measurements at ZEUS

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    Results on the diffractive structure function F-2(D(3)) in deep inelastic neutral current positron-proton scattering (DIS) have been obtained by the ZEUS collaboration using two different methods. Diffractive interactions are selected by either requiring a small, not exponentially suppressed invariant hadronic mass M-X in the main detector or by detecting a fast proton in the ZEUS leading proton spectrometer (LPS). The results of the two methods are compared
    Archivio della Ricerca - Università di Roma 3

    Fragmentation functions at ZEUS

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    The scaled momentum spectra of final state charged hadrons produced in Deep Inelastic Scattering in the ranges 10 < Q(2) < 1280 GeV2 and 6 . 10(-4) < x(Bjorken) < 5 . 10(-2) have been measured in the current region of the Breit frame using the ZEUS detector. The evolution with Q(2) of the scaled momentum, x(p) = 2p(Breit)/Q, has been investigated and preliminary results are presented which show evidence for scaling violations and support for the universality of quark fragmentation
    Archivio della Ricerca - Università di Roma 3

    Measurement of the proton structure function F-2 and the total gamma*p cross-section at low Q(2) and low x

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    The ZEUS-experiment at HERA has significantly enhanced the kinematic coverage for low Q(2) and low x inelastic e(+)p --> e(+) X scattering with an upgrade of the ZEUS-detector in 1995 which extends the acceptance for small positron scattering angles. The upgrade included the modification of the beam pipe with low mass exit windows and the installation of a small electromagnetic sampling calorimeter, the Beam Pipe Calorimeter (BPC), to explore the region in Q(2) of 0.11 less than or equal to Q(2) less than or equal to 0.65 GeV2. A shift of two rear uranium calorimeter (RCAL) modules and the small rear tracking detector (SRTD) closer to the beam together with a data sample taken with a shifted event vertex extended the Q(2) coverage of the main detector down to 0.6 GeV2. Both data sets have been used to measure the proton structure function F-2 and the total virtual photonproton gamma*p cross-section. Results are presented for 0.11 less than or equal to Q(2) less than or equal to 6.10 GeV2 and 2.10(-6) less than or equal to x less than or equal to 7.10(-4) along with a comparison to various models
    Archivio della Ricerca - Università di Roma 3

    Leading baryons at low x(L) in DIS and photoproduction at ZEUS

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    Results obtained by the ZEUS collaboration on leading baryon production in the proton fragmentation region are presented. The reaction gamma p --> NX, with N a proton or a neutron, is examined both at low and high photon virtuality
    Archivio della Ricerca - Università di Roma 3

    Measurement of dijets in DIS and comparison to NLO calculations

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    We report a measurement of the dijet production cross section in neutral current deep inelastic scattering with the ZEUS detector at the HERA ep collider. Dijet events are identified with the cone algorithm and the results are compared to next-to-leading order perturbative QCD calculations. The systematic uncertainties of both the measurement and the calculation we discussed
    Archivio della Ricerca - Università di Roma 3
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