Results 1 - 10 of 8045
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[en] We have measured the mean lifetime tau of the free neutron by counting decay protons stored in an electromagnetic trap. Neutron density determination was by activation of calibrated boron foils. The result, based on five independent measurements for various experimental conditions, is tau = 937 +- 18 s. (orig.)
[en] At this stage of the LHC (Large Hadron Collider) program, the prospect for a new physics signal in the very rare K → Kνν-bar decays may be dented, but remains well alive thanks to their intrinsic qualities. First, these decays are among the cleanest observables in the quark flavor sector. When combined with their terrible suppression in the SM (Standard Model), they thus offer uniquely sensitive probes. Second, the LHC capabilities are not ideal for all kinds of new physics, even below the TeV scale. For example, rather elusive scenarios like natural-SUSY-like hierarchical spectrum, baryon number violation, or new very light but very weakly interacting particles may well induce deviations in rare K decays. Even though experimentalists should brace themselves for tiny deviations, these modes thus have a clear role to play in the LHC era. (author)
[en] A long distance contribution to the amplitude for K+→π+νν(bar sign) is calculated. Its magnitude, comparable to that of other long distance effects, is three orders of magnitude smaller than the short distance effects, but the techniques involved may have other applications. (c) 2000 The American Physical Society
[en] In this work a nonrelativistic model for hadronic matrix elements of the charged current is derived. First the stability of mesons made of heavy quarks is described. Then some general qualitative remarks on semileptonic hadron decays follow. After fixing the parametrisation of the form factors numerical bounds for certain semileptonic width ratios of pseudoscalar mesons are given. Subsequently, from the assumption of a local duality, form factors for weakly bound mesons are derived. Then the dependence of the form factors on the transfered momentum is considered. After these considerations a nonrelativistic model for hadronic matrix elements of the charged weak current between two (S-state) hadrons (mesons or baryons) is developed, which is symmetric between the two hadrons in the static approximation and depends on the effective spectator masses. For mesons the results are similar to those of other nonrelativistic models. For baryons the method is a lot less elegant than for mesons, since the baryon spinor cannot usefully be split up into a sum of quark spinors. (author)
[en] We establish two theorems that show that it is not possible to uniquely determine experimentally all of the relevant form factors involved in hyperon semileptonic decays, when an electron or positron is emitted and the hyperons are unpolarized. (orig.)
[en] Five different hyperon semileptonic decays have been made by the WA2 experiment. The results are summarized. The WA2 collaboration have performed a Cabibbo fit using only one datum not from the WA2 experiment. The fit gives a Λ2/df of 4.5/5. Other fits are mentioned. (U.K.)
[en] We show prospects for research of invisible decays of B meson in a sample of about 470 millions BB pairs recorded with the BABAR detector at the SLAC PEP-II B factory. The Standard Model predictions for a B decay with completely invisible final products (or with a single photon as detectable particle) are far from the current experimental sensitivities but several New Physics Models predict significant enhancements on the branching ratio of these decays. The analysis technique consists in the reconstruction of a semileptonic B decay on one side and in the search of missing energy or missing energy plus one photon in the recoil. We will describe the search techniques and provide the expected sensitivities for these decays.
[en] Neutron beta decay is described accurately within the standard model of particle physics using the first CKM-matrix element, Vud, and the ratio of vector and axial vector couplings, λ, as parameters. Angular correlations, spectra and the neutron lifetime are accessible experimentally, providing an excellent toolkit for investigating the structure of weak interaction. Measuring the Beta Asymmetry, A, is the most precise way of determining λ, which is an important standard model parameter and necessary for the determination of Vud from Neutron Decay. Moreover it allows to derive limits on non-standard model couplings by combining with measurements of other correlation coefficients. In this talk we present the most precise measurement of the Beta Asymmetry performed with the decay spectrometer Perkeo III carried out at the PF1B cold neutron beam facility at the Institut Laue-Langevin. We discuss the result and its implications.
[en] We present the status of the data analysis of the recent measurement of the proton asymmetry in neutron beta decay with Perkeo III. This first direct measurement using a pulsed neutron beam and a proton retardation system will improve the first indirect measurement of the proton asymmetry, which has been performed with Perkeo II. Measuring the proton asymmetry allows searches for physics beyond axialvector and vector couplings of the Standard Model when combined with measurements of other correlation coefficients of neutron beta decay.