470 research outputs found

    Measurement of the t distribution in diffractive photoproduction at HERA

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    Photon diffractive dissociation, γp → Xp, has been studied at HERA with the ZEUS detector using ep interactions where the virtuality Q2 of the exchanged photon is smaller than 0.02 GeV2. The squared four-momentum t exchanged at the proton vertex was determined in the range 0.073 < \t\ < 0.40 GeV2 by measuring the scattered proton in the ZEUS Leading Proton Spectrometer. In the photonproton centre-of-mass energy interval 176 < W < 225 GeV and for masses of the dissociated photon system 4 < Mx < 32 GeV, the t distribution has an exponential shape, dN/d\t\ ∝ exp (-b\t\), with a slope parameter b = 6.8 ± 0.9 (stat.) +1.2-1.1 (syst.) GeV-2

    Measurement of the E**2(T,jet) / Q**2 dependence of forward jet production at HERA

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    The forward-jet cross section in deep inelastic e(+)p scattering has been measured using the ZEUS detector at HERA with an integrated luminosity of 6.36 pb(-1). The jet cross section is presented as a function of jet transverse energy squared, E-T,jet(2), and Q(2) in the kinematic ranges 10(-2) lt E-T,jet(2)/Q(2) lt 10(2) and 2.5.10(-4) lt x lt 8.0.10(-2). Since the perturbative QCD predictions for this cross section are sensitive to the treatment of the log(E-T,jet(2)/Q(2)) terms, this measurement provides an important test. The measured cross section is compared to the predictions of a next-to-leading order pQCD calculation as well as to various leading-order Monte Carlo models. Whereas the predictions of all models agree with the measured cross section in the region of small E- T,jet(2)/Q(2), only one model, which includes a resolved photon component, describes the data over the whole kinematic range

    Observation of isolated high-E-T photons in deep inelastic scattering

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    First measurements of cross sections for isolated prompt photon production in deep inelastic ep scattering have been made using the ZEUS detector at the HERA electron-proton collider using an integrated luminosity of 121 pb(-1). A signal for isolated photons in the transverse energy and rapidity ranges 5 lt E-T(y) lt 10 GeV and -0.7 lt eta(gamma) lt 0.9 was observed for virtualities of T the exchanged photon of Q(2) gt 35 GeV2. Cross sections are presented for inclusive prompt photons and for those accompanied by a single jet in the range E-jet(T) greater than or equal to 6 GeV and 1.5 less than or equal to eta(jet) lt 1.8. Calculations at order alpha(3)alpha(s), describe the data reasonably well

    Measurement of the t distribution in diffractive photoproduction at HERA

    No full text
    Photon diffractive dissociation, γp → Xp, has been studied at HERA with the ZEUS detector using ep interactions where the virtuality Q2 of the exchanged photon is smaller than 0.02 GeV2. The squared four-momentum t exchanged at the proton vertex was determined in the range 0.073 &lt;\t\ &lt;0.40 GeV2 by measuring the scattered proton in the ZEUS Leading Proton Spectrometer. In the photonproton centre-of-mass energy interval 176 &lt;W &lt;225 GeV and for masses of the dissociated photon system 4 &lt;Mx &lt;32 GeV, the t distribution has an exponential shape, dN/d\t\ ∝ exp (-b\t\), with a slope parameter b = 6.8 ± 0.9 (stat.) +1.2-1.1 (syst.) GeV-2

    Measurement of the t distribution in diffractive photoproduction at HERA

    No full text
    Photon diffractive dissociation, γp → Xp, has been studied at HERA with the ZEUS detector using ep interactions where the virtuality Q2 of the exchanged photon is smaller than 0.02 GeV2. The squared four-momentum t exchanged at the proton vertex was determined in the range 0.073 &lt;\t\ &lt;0.40 GeV2 by measuring the scattered proton in the ZEUS Leading Proton Spectrometer. In the photonproton centre-of-mass energy interval 176 &lt;W &lt;225 GeV and for masses of the dissociated photon system 4 &lt;Mx &lt;32 GeV, the t distribution has an exponential shape, dN/d\t\ ∝ exp (-b\t\), with a slope parameter b = 6.8 ± 0.9 (stat.) +1.2-1.1 (syst.) GeV-2

    Measurement of the <i>t</i> dependence in exclusive photoproduction of &#978;(1 <i>S</i>) mesons at HERA

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    The exclusive photoproduction reaction γp&#8594;&#978;(1 &lt;i&gt;S&lt;/i&gt;)&lt;i&gt;p&lt;/i&gt; has been studied with the ZEUS detector in &lt;i&gt;ep&lt;/i&gt; collisions at HERA using an integrated luminosity of 468 pb&lt;sup&gt;−1&lt;/sup&gt;. The measurement covers the kinematic range60&#60;W&#60;220 GeV and Q&lt;sup&gt;2&lt;/sup&gt;&#60;1 GeV&lt;sup&gt;2&lt;/sup&gt;, where &lt;i&gt;W&lt;/i&gt; is the photon–proton centre-of-mass energy and Q&lt;sup&gt;2&lt;/sup&gt; is the photon virtuality. The exponential slope, &lt;i&gt;b&lt;/i&gt;, of the &lt;i&gt;t&lt;/i&gt; dependence of the cross section, where &lt;i&gt;t&lt;/i&gt; is the squared four-momentum transfer at the proton vertex, has been measured, yielding b = 4.3{+2.0 =1.3}(stat.){+0.5 -0.6}(syst.) GeV&lt;sup&gt;-2&lt;/sup&gt;. This constitutes the first measurement of the &lt;i&gt;t&lt;/i&gt; dependence of the γp&#8594;&#978;(1 &lt;i&gt;S&lt;/i&gt;)&lt;i&gt;p&lt;/i&gt; cross section

    A measurement of the Q(2), W and t dependences of deeply virtual Compton scattering at HERA

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    Deeply virtual Compton scattering, γ*p→γp has been measured in e+p collisions at HERA with the ZEUS detector using an integrated luminosity of 61.1 pb-1. Cross sections are presented as a function of the photon virtuality, Q2, and photon-proton centre-of-mass energy, W, for a wide region of the phase space, Q2 > 1.5GeV2 and 40 < W < 170GeV. A subsample of events in which the scattered proton is measured in the leading proton spectrometer, corresponding to an integrated luminosity of 31.3 pb-1, is used for the first direct measurement of the differential cross section as a function of t, where t is the square of the four-momentum transfer at the proton vertex. © SISSA 2009

    Observation of isolated high E(t) photons in photoproduction at HERA

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    Events containing an isolated prompt photon with high transverse energy, together with a balancing jet, have been observed for the first time in photoproduction at HERA. The data were taken with the ZEUS detector, in a gamma p centre of mass energy range 120-250 GeV. The fraction of the incoming photon energy participating in the production of the prompt photon and the jet, x(gamma), shows a strong peak near unity, consistent with LO QCD Monte Carlo predictions. In the transverse energy and pseudorapidity range 5 less than or equal to E-T(gamma) 0.8, the measured cross section is 15.3 +/- 3.8 +/- 1.8 ph, in good agreement with a recent NLO calculation

    Combined inclusive diffractive cross sections measured with forward proton spectrometers in deep inelastic ep scattering at HERA

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    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 improved precision of the cross section measurement which reaches 6 % for the most precise points. The combined data cover the range 2.5 < Q 2 < 200 GeV 2 in photon virtuality, 0.00035 < xP < 0.09 in proton fractional momentum loss, 0.09 <{pipe}t{pipe}< 0.55 GeV 2 in squared four-momentum transfer at the proton vertex and 0.0018 < β <0.816 in β=x/xP, where x is the Bjorken scaling variable. © 2012 The Author(s).0H1 and ZEUS CollaborationsSCOPUS: ar.jinfo:eu-repo/semantics/publishe
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