Diffractive photoproduction of vector mesons, \(\gamma p \to V Y\), where Y is a proton-dissociative system, has been measured in e+p interactions with the ZEUS detector at HERA using an integrated ...luminosity of 25\(\pbi\). The differential cross section, \(d\sigma/d t\), is presented for \(1.2 < -t<12{\rm GeV}^2\), where t is the square of the four-momentum transferred to the vector meson. The data span the range in photon-proton centre-of-mass energy, W, from 80 GeV to 120 GeV. The t distributions are well fit by a power law, \(d\sigma/d t \propto (-t)^{-n}\). The slope of the effective Pomeron trajectory, measured from the W dependence of the \(\rho^0\) and \(\phi\) cross sections in bins of t, is consistent with zero. The ratios \(d\sigma_{\gamma p \to \phi Y}/d t\) to \(d\sigma_{\gamma p \to \rho^0 Y}/d t\) and \(d\sigma_{\gamma p \to J/\psi Y}/d t\) to \(d\sigma_{\gamma p \to \rho^0 Y}/d t\) increase with increasing -t. Decay-angle analyses for \(\rho^0\), \(\phi\) and \(J/\psi\) mesons have been carried out. For the \(\rho^0\) and \(\phi\) mesons, contributions from single and double helicity flip are observed. The results are compared to expectations of theoretical models.
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DOBA, FZAB, GEOZS, IJS, IMTLJ, IZUM, KILJ, KISLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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<ETγ<10GeV and −0.7<ηγ<0.9 was observed for virtualities of the exchanged photon of Q2>35GeV2. Cross sections are presented for inclusive prompt photons and for those accompanied by a single jet in the range ETjet⩾6GeV and −1.5⩽ηjet<1.8. Calculations at order α3αs describe the data reasonably well.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Bose–Einstein correlations of charged and neutral kaons have been measured in e±p deep inelastic scattering with an integrated luminosity of 121 pb−1 using the ZEUS detector at HERA. The two-particle ...correlation function was studied as a function of the four-momentum difference of the kaon pairs, Q12=−(p1−p2)2, assuming a Gaussian shape for the particle source. The values of the radius of the production volume, r, and of the correlation strength, λ, were obtained for both neutral and charged kaons. The radii for charged and neutral kaons are similar and are consistent with those obtained at LEP.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The production of D super(c)- and D super(0)-mesons has been measured with the ZEUS detector at HERA using an integrated luminosity of 133.6 pb super(-1). The measurements cover the kinematic range ...5<Q super(2)<1000 GeV super(2), 0.02<y<0.7, 1.5<p sub(T) super(D )<15 GeV and
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DOBA, FZAB, GEOZS, IJS, IMTLJ, IZUM, KILJ, KISLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Inclusive K_{S};{0}K_{S};{0} production in ep collisions at the DESY ep collider HERA was studied with the ZEUS detector using an integrated luminosity of 0.5 fb;{-1}. Enhancements in the mass ...spectrum were observed and are attributed to the production of f_{2}(1270)/a_{2};{0}(1320), f_{2};{'}(1525) and f_{0}(1710). Masses and widths were obtained using a fit which takes into account theoretical predictions based on SU(3) symmetry arguments, and are consistent with the Particle Data Group values. The f_{0}(1710) state, which has a mass consistent with a glueball candidate, was observed with a statistical significance of 5 standard deviations. However, if this state is the same as that seen in gammagamma-->K_{S};{0}K_{S};{0}, it is unlikely to be a pure glueball state.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
The dependence of dijet production on the virtuality of the exchanged photon, Q2, has been studied by measuring dijet cross sections in the range \(0 \lesssim Q^2 < 2000 {\;\rm GeV}^2\) with the ZEUS ...detector at HERA using an integrated luminosity of 38.6 pb-1. Dijet cross sections were measured for jets with transverse energy \(E_T^{\rm jet} > 7.5\) and 6.5 GeV and pseudorapidities in the photon-proton centre-of-mass frame in the range \(-3 < \eta^{\rm jet} < 0\). The variable \(x^{\rm obs}_{\gamma}\), a measure of the photon momentum entering the hard process, was used to enhance the sensitivity of the measurement to the photon structure. The Q2 dependence of the ratio of low- to high- \(\smashb x^{\rm obs}_{\gamma} \) events was measured. Next-to-leading-order QCD predictions were found to generally underestimate the low- \(\smasht x^{\rm obs}_{\gamma} \) contribution relative to that at high \(\smasht x^{\rm obs}_{\gamma} \). Monte Carlo models based on leading-logarithmic parton-showers, using a partonic structure for the photon which falls smoothly with increasing Q2, provide a qualitative description of the data.
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DOBA, FZAB, GEOZS, IJS, IMTLJ, IZUM, KILJ, KISLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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