Abstract: We report the results of a study of the exclusive charmless semileptonic decays, B-0 -> pi(-)l(+)nu, B+ -> pi(0)l(+)nu, B+ -> omega l(+)nu, B+ -> eta l(+)nu, and B+ -> eta'l(+)nu (l = e or mu) undertaken with approximately 462 X 10(6) B (B) over bar pairs collected at the Upsilon(4S) resonance with the BABAR detector. The analysis uses events in which the signal B decays are reconstructed with a loose neutrino reconstruction technique. We obtain partial branching fractions in several bins of q(2), the square of the momentum transferred to the lepton-neutrino pair, for B-0 -> pi(-)l(+)nu, B+ -> pi(0)l(+)nu, B+ -> omega l(+)nu, and B+ -> eta l(+)nu. From these distributions, we extract the form-factor shapes f(+)(q(2)) and the total branching fractions B(B-0 -> pi(-)l(+)nu) = (1.45 +/- 0.04(stat) +/- 0.06(syst)) X 10(-4) (combined pi(-) and pi(0) decay channels assuming isospin symmetry), B(B+ -> omega l(+)nu) = (1.19 +/- 016(stat) +/- 0.09(syst)) X 10(-4) and B(B+ -> eta l(+)nu) = (0.38 +/- 0.05(stat) +/- 0.05(syst)) X 10(-4). We also measure B(B+ -> eta'l(+)nu) = (0.24 +/- 0.08(stat) +/- 0.03(syst)) X 10(-4). We obtain values for the magnitude of the Cabibbo-Kobayashi-Maskawa (KM) matrix element vertical bar V-ub vertical bar by direct comparison with three different QCD calculations in restricted q(2) ranges of B -> pi l(+)nu decays. From a simultaneous fit to the experimental data over the full q(2) range and the FNAL/MILC lattice QCD predictions, we obtain vertical bar V-ub vertical bar = (3.25 +/- 0.31) X 10(-3), where the error is the combined experimental and theoretical uncertainty.

Abstract: The branching ratios of K- absorption in nuclear matter are theoretically investigated in order to understand the mechanism of K- absorption into nuclei. For this purpose mesonic and nonmesonic absorption potentials are evaluated as functions of nuclear density, the kaon momentum, and energy from one- and two-body K- self-energy, respectively. By using a chiral unitary approach for the s-wave (K) over bar N amplitude we find that both the mesonic and nonmesonic absorption potentials are dominated by the Lambda(1405) contributions. The fraction of the mesonic and nonmesonic absorptions are evaluated to be respectively about 70% and 30% at the saturation density almost independently of the kaon momentum. We also observe different behavior of the branching ratios to pi(+)Sigma(-) and pi(-)Sigma(+) channels in mesonic absorption due to the interference between Lambda(1405) and the I = 1 nonresonant background, which is consistent with experimental results. The nonmesonic absorption ratios [Lambda p]/[Sigma(0)p] and [Lambda n]/[Sigma(0)n] are about unity while [Sigma(+)n]/[Sigma(0)p] and [Sigma(-) p]/[Sigma(0)n] are about 2 due to the Lambda(1405) dominance in absorption. Taking into account the kaon momenta and energies, the absorption potentials become weaker due to the downward shift of the initial K- N two-body energy, but this does not drastirally change the nonmesonic fraction. The Sigma(1385) contribution in the p-wave (K) over bar N amplitude is examined and found to be very small compared to the Lambda(1405) contribution in slow K- absorption.

Abstract: A sizeable difference in the differential production cross section of top-compared to antitop-quark production, denoted charge asymittetm has been observed at the Tevatron. The experimental results seem to exceed the theory predictions based on the Standard Model by a significant amount and have triggered a large number of suggestions for “new physics'. In the present paper the Standard Model predictions for Tevatron and LHe experiments are revisited. This includes a reanalysis of electromagnetic as well as weak corrections, leading to a shift of the asymmetry by roughly a factor 1.1 when compared to the results of the first papers on this subject. The impact of cuts on the transverse momentum of the top-antitop system is studied. Restricting the it system to a transverse momentum less than 20 GeV leads to an enhancement of the asymmetries by factors between 1.3 and 1.5, indicating the importance of an improved understanding of the tt-momentum distribution. Predictions for similar measurements at the LHC are presented, demonstrating the sensitivity of the large rapidity region bot ti to the Standard Model contribution and effects from ”new physics".