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Abstract:

The photoproduction of bottom quarks in events with two jets and a muon has been measured with the ZEUS detector at HERA using an integrated luminosity of 110 pb-1. The fraction of jets containing b quarks was extracted from the transverse momentum distribution of the muon relative to the closest jet. Differential cross sections for bottom production as a function of the transverse momentum and pseudorapidity of the muon, of the associated jet and of xγjets, the fraction of the photon's momentum participating in the hard process, are compared with MC models and QCD predictions made at next-to-leading order. The latter give a good description of the data.

Abstract:

A resonance search has been made in the K⁰Sp and K⁰Sp̄ invariant-mass spectrum measured with the ZEUS detector at HERA using an integrated luminosity of 121 pb^-1. The search was performed in the central rapidity region of inclusive deep inelastic scattering at an ep centre-of-mass energy of 300-318 GeV for exchanged photon virtuality, Q², above 1 GeV². Recent results from fixed-target experiments give evidence for a narrow baryon resonance decaying to K⁺n and K⁰Sp, interpreted as a pentaquark. The results presented here support the existence of such state, with a mass of 1521.5±1.5(stat.)^+2.8-1.7(syst.) MeV and a Gaussian width consistent with the experimental resolution of 2 MeV. The signal is visible at high Q² and, for Q²>20 GeV², contains 221±48 events. The probability of a similar signal anywhere in the range 1500-1560 MeV arising from fluctuations of the background is below 6×10^-5. © 2004 Elsevier B.V. All rights reserved.

Abstract:

A search for physics beyond the Standard Model has been performed with high-Q² neutral current deep inelastic scattering events recorded with the ZEUS detector at HERA. Two data sets, e⁺��→e ⁺X and e^-��→e^-X, with respective integrated luminosities of 112 pb^-1 and 16 pb^-1, were analyzed. The data reach Q² values as high as 40000 GeV². No significant deviations from Standard Model predictions were observed. Limits were derived on the effective mass scale in eeqq contact interactions, the ratio of leptoquark mass to the Yukawa coupling for heavy leptoquark models and the mass scale parameter in models with large extra dimensions. The limit on the quark charge radius, in the classical form factor approximation, is 0.85×10 ^-16 cm. © 2004 Published by Elsevier B.V.

Abstract:

The photoproduction of D^*±(2010) mesons associated with a leading neutron has been observed with the ZEUS detector in ep collisions at HERA using an integrated luminosity of 80 pb^-1. The neutron carries a large fraction, xL>0.2, of the incoming proton beam energy and is detected at very small production angles, θn< 0.8 mrad, an indication of peripheral scattering. The D^* meson is centrally produced with pseudorapidity η<1.5, and has a transverse momentum pT>1.9 GeV, which is large compared to the average transverse momentum of the neutron of 0.22 GeV. The ratio of neutron-tagged to inclusive D^* production is 8.85±0.93(stat.) ^+0.48-0.61(syst.)% in the photon-proton center-of-mass energy range 130