Professor Amanda Cooper-Sarkar

Abstract:

The production of D ^±- and D ⁰-mesons has been measured with the ZEUS detector at HERA using an integrated luminosity of 133.6 pb^-1. The measurements cover the kinematic range 52<1000 GeV², 0.02T ^D <15 GeV and |η ^D |<1.6. Combinatorial background to the D-meson signals is reduced by using the ZEUS microvertex detector to reconstruct displaced secondary vertices. Production cross sections are compared with the predictions of next-to-leading-order QCD, which is found to describe the data well. Measurements are extrapolated to the full kinematic phase space in order to obtain the open-charm contribution, F^cc 2 to the proton structure function, F 2. © 2009 Springer-Verlag / Società Italiana di Fisica.

Abstract:

Measurements of the neutral current cross sections for deep inelastic scattering in e ^- p collisions at HERA with a longitudinally polarised electron beam are presented. The single-differential cross-sections d σ/dQ ², d σ/dx and d σ/dy and the double-differential cross sections in Q ² and x are measured in the kinematic region y<0.9 and Q ²>185∈GeV ² for both positively and negatively polarised electron beams and for each polarisation state separately. The measurements are based on an integrated luminosity of 169.9∈pb ^-1 taken with the ZEUS detector in 2005 and 2006 at a centre-of-mass energy of 318∈GeV. The structure functions F3 and xF 3 ^{γ Z} are determined by combining the e ^- p results presented in this paper with previously measured e ⁺ p neutral current data. The asymmetry parameter A ^- is used to demonstrate the parity violating effects of electroweak interactions at large spacelike photon virtuality. The measurements agree well with the predictions of the Standard Model. © 2009 Springer-Verlag / Società Italiana di Fisica.

Abstract:

The dissociation of virtual photons, γ^{{star operator}} p → X p, in events with a large rapidity gap between X and the outgoing proton, as well as in events in which the leading proton was directly measured, has been studied with the ZEUS detector at HERA. The data cover photon virtualities Q² > 2   GeV² and γ^{{star operator}} p centre-of-mass energies 40 < W < 240   GeV, with MX > 2   GeV, where MX is the mass of the hadronic final state, X. Leading protons were detected in the ZEUS leading proton spectrometer. The cross section is presented as a function of t, the squared four-momentum transfer at the proton vertex and Φ, the azimuthal angle between the positron scattering plane and the proton scattering plane. It is also shown as a function of Q² and xP, the fraction of the proton's momentum carried by the diffractive exchange, as well as β, the Bjorken variable defined with respect to the diffractive exchange. © 2009 Elsevier B.V.