Professor Brian Foster OBE, FRS

Abstract:

Diffractive production of D*±(2010) mesons in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 44.3 pb-1. Diffractive charm production is identified by the presence of a large rapidity gap in the final state of events in which a D*±(2010) meson is reconstructed in the decay channel D*+ → (D0 → K-π+)πs+ (+ charge conjugate). Differential cross sections when compared with theoretical predictions indicate the importance of gluons in such diffractive interactions. © 2002 Elsevier Science B.V. All rights reserved.

Abstract:

Diffractive dissociation of virtual photons, γ*p → Xp, has been studied in ep interactions with the ZEUS detector at HERA. The data cover photon virtualities 0.17 < Q2 < 0.70 GeV2 and 3 < Q2 < 80 GeV2 with 3 < MX < 38 GeV, where MX is the mass of the hadronic final state. Diffractive events were selected by two methods: the first required the detection of the scattered proton in the ZEUS leading proton spectrometer (LPS); the second was based on the distribution of MX. The integrated luminosities of the low- and high-Q2 samples used in the LPS-based analysis are ≃ 0.9 pb-1 and ≃ 3.3 pb-1, respectively. The sample used for the MX-based analysis corresponds to an integrated luminosity of ≃ 6.2 pb-1. The dependence of the diffractive cross section on W, the virtual photon-proton centre-of-mass energy, and on Q2 is studied. In the low-Q2 range, the energy dependence is compatible with Regge theory and is used to determine the intercept of the Pomeron trajectory. The W dependence of the diffractive cross section exhibits no significant change from the low-Q2 to the high-Q2 region. In the low-Q2 range, little Q2 dependence is found, a significantly different behaviour from the rapidly falling cross section measured for Q2 > 3 GeV2. The ratio of the diffractive to the virtual photon-proton total cross section is studied as a function of W and Q2. Comparisons are made with a model based on perturbative QCD.

Abstract:

We present a measurement of time-dependent CP-violating asymmetries in neutral B meson decays collected with the BABAR detector at the PEP-II asymmetric-energy e+e-collider at the Stanford Linear Accelerator Center. The data sample consists of 29.7 fb-1recorded at the Υ(4S) resonance and 3.9 fb-1off resonance. One of the neutral B mesons, which are produced in pairs at the Υ(4S), is fully reconstructed in the CP decay modes J/ΨKS0, Ψ(2S)KS0, Xc1KS0, J/ΨK*0(K*0→Ks0π0) and J/ΨKL0, or in flavor-eigenstate modes involving D(*)π/ρ/a1and J/ΨK*0(K*0→K+π-). The flavor of the other neutral B meson is tagged at the time of its decay, mainly with the charge of identified leptons and kaons. A neural network tagging algorithm is used to recover events without a clear lepton or kaon tag. The proper time elapsed between the decays is determined by measuring the distance between the decay vertices. Wrong-tag probabilities, the time-difference resolution function, and the B0-B̄0oscillation frequency Δmdare measured with a sample of about 6350 fully-reconstructed B0decays in hadronic flavor-eigenstate modes. A maximum-likelihood fit to this flavor eigenstate sample finds Δmd=0.516±0.016(stat)±0.010(syst) ps-1. The value of the asymmetry amplitude sin 2Β is determined from a simultaneous maximum-likelihood fit to the time-difference distribution of the flavor-eigenstate sample and about 642 tagged B0decays in the CP-eigenstate modes. We find sin 2Β=0.59 ±0.14(stat)±0.05(syst), demonstrating that CP violation exists in the neutral B meson system. We also determine the value of the CP violation parameter |λ|=0.93±0.09(stat)±0.03(syst), which is consistent with the expectation of |λ|=1 for no direct CP violation.