51�������

Abstract:

The world-wide situation with respect to proposed new accelerators is reviewed. Concentrating on Europe, and on machines designed by the particle physics community represented by the European Committee for Future Accelerators (ECFA), the prospects for new high-intensity accelerators to address specific questions are discussed and possible scenarios outlined.

Abstract:

The ZEUS inclusive differential cross-section data from HERA, for charged and neutral current processes taken with e ⁺ and e ^- beams, together with differential cross-section data on inclusive jet production in e ⁺ p scattering and dijet production in γp scattering, have been used in a new NLO QCD analysis to extract the parton distribution functions of the proton. The input of jet-production data constrains the gluon and allows an accurate extraction of alpha s(MZ) at NLO; alphas = 0.1183±0.0028(exp.)±0.0008(model). An additional uncertainty from the choice of scales is estimated as ±0.005. This is the first extraction of alphas(MZ) from HERA data alone. © Springer-Verlag/Società Italiana de Fisica 2005.

Abstract:

Deep inelastic scattering and its diffractive component, ep → e′ γ* p → e′ X N, have been studied at HERA with the ZEUS detector using an integrated luminosity of 4.2 pb^-1. The measurement covers a wide range in the γ* p c.m. energy W (37-245 GeV), photon virtuality Q² (2.2-80 GeV²) and mass MX (0.28-35 GeV). The diffractive cross section for MX > 2 GeV rises strongly with W; the rise is steeper with increasing Q². The latter observation excludes the description of diffractive deep inelastic scattering in terms of the exchange of a single pomeron. The ratio of diffractive to total cross section is constant as a function of W, in contradiction to the expectation of Regge phenomenology combined with a naive extension of the optical theorem to γ* p scattering. Above MX of 8 GeV, the ratio is flat with Q², indicating a leading-twist behaviour of the diffractive cross section. The data are also presented in terms of the diffractive structure function, F2^D(3)(β, xℙ, Q²), of the proton. For fixed β, the Q² dependence of xℙF2 ^D(3) changes with xℙ in violation of Regge factorisation. For fixed xℙ, xℙ F2^D(3) rises as β → 0, the rise accelerating with increasing Q². These positive scaling violations suggest substantial contributions of perturbative effects in the diffractive DIS cross section. © 2005 Elsevier B.V. All rights reserved.

Abstract:

A search for pentaquarks decaying to Ξ-π- (Ξ-π+) and corresponding antiparticles has been performed with the ZEUS detector at HERA. The data sample consists of deep inelastic ep scattering events at centre-of-mass energies of 300 and 318 GeV, and corresponds to 121 pb ^-1 of integrated luminosity. A clear signal for Ξ0(1530) →Ξ-π+ was observed. However, no signal for any new baryonic state was observed at higher masses in either the Ξ-π- or Ξ-π+ channels. The searches in the antiparticle channels were also negative. Upper limits on the ratio of a possible Ξ3/2 - (Ξ3/20) signal to the Ξ0(1530) signal were set in the mass range 1650-2350 MeV. © 2005 Elsevier B.V. All rights reserved.

Abstract:

Energetic neutrons produced in ep collisions at HERA have been studied with the ZEUS detector in the photoproduction regime at a mean photon-proton center-of-mass energy of 220 GeV. The neutrons carry a large fraction 0.64