Search results for " Standard Model"
showing 10 items of 645 documents
Improved $K_{e3}$ radiative corrections sharpen the $K_{\mu 2}$--$K_{l3}$ discrepancy
2021
The measurements of $V_{us}$ in leptonic $(K_{\mu 2})$ and semileptonic $(K_{l3})$ kaon decays exhibit a $3\sigma$ disagreement, which could originate either from physics beyond the Standard Model or some large unidentified Standard Model systematic effects. Clarifying this issue requires a careful examination of all existing Standard Model inputs. Making use of a newly-proposed computational framework and the most recent lattice QCD results, we perform a comprehensive re-analysis of the electroweak radiative corrections to the $K_{e3}$ decay rates that achieves an unprecedented level of precision of $10^{-4}$, which improves the current best results by almost an order of magnitude. No larg…
A general parametrization for the long-range part of neutrinoless double beta decay
1997
Double beta decay has been proven to be a powerful tool to constrain $B-L$ violating physics beyond the standard model. We present a representation for the long-range part of the general $0\nu\beta\beta$ decay rate allowed by Lorentz-invariance. Combined with the short range part this general parametrization in terms of effective $B-L$ violating couplings will provide the $0\nu\beta\beta$ limits on arbitrary lepton number violating theories.
Weak Polarized Electron Scattering
2014
Scattering polarized electrons provides an important probe of the weak interactions. Precisely measuring the parity-violating left-right cross section asymmetry is the goal of a number of experiments recently completed or in progress. The experiments are challenging, since A_{LR} is small, typically between 10^(-4) and 10^(-8). By carefully choosing appropriate targets and kinematics, various pieces of the weak Lagrangian can be isolated, providing a search for physics beyond the Standard Model. For other choices, unique features of the strong interaction are studied, including the radius of the neutron density in heavy nuclei, charge symmetry violation, and higher twist terms. This article…
Neutrino oscillations and new physics
2005
I discuss the theoretical background and the status of neutrino oscillation parameters from the current worlds' global data sample and latest flux calculations. I give their allowed ranges, best fit values and discuss the small parameters and sin2theta13, which characterize CP violation in neutrino oscillations. I mention the significance of neutrinoless double beta decay and current expectations in view of oscillation results.
Improved limits onB0decays to invisible(+γ)final states
2012
We establish improved upper limits on branching fractions for B-0 decays to final states where the decay products are purely invisible (i.e., no observable final state particles) and for final states where the only visible product is a photon. Within the Standard Model, these decays have branching fractions that are below the current experimental sensitivity, but various models of physics beyond the Standard Model predict significant contributions for these channels. Using 471 x 10(6) B (B) over bar pairs collected at the Upsilon(4S) resonance by the BABAR experiment at the PEP-II e(+)e(-) storage ring at the SLAC National Accelerator Laboratory, we establish upper limits at the 90% confide…
Search for new physics inlepton+photon+Xevents with929 pb−1ofpp¯collisions ats=1.96 TeV
2007
The authors present results of a search for anomalous production of events containing a charged lepton ({ell}, either e or {mu}) and a photon ({gamma}), both with high transverse momentum, accompanied by additional signatures, X, including missing transverse energy (E{sub T}) and additional leptons and photons. We use the same kinematic selection criteria as in a previous CDF search, but with a substantially larger data set, 305 pb{sup -1}, a p{bar p} collision energy of 1.96 TeV, and the upgraded CDF II detector. We find 42 {ell}{gamma}E{sub T} events versus a standard model expectation of 37.3 {+-} 5.4 events. The level of excess observed in Run I, 16 events with an expectation of 7.6 {+-…
Leptonic universality breaking in Upsilon decays as a probe of new physics
2003
In this work we examine the possible existence of new physics beyond the standard model which could modify the branching fractions of the leptonic (mainly tauonic) decays of bottomonium vector resonances below the $B\bar{B}$ threshold. The decay width is factorized as the product of two pieces: a) the probability of an intermediate pseudoscalar color-singlet $b\bar{b}$ state (coupling to the dominant Fock state of the Upsilon via a magnetic dipole transition) and a soft (undetected) photon; b) the annihilation width of the $b\bar{b}$ pair into two leptons, mediated by a non-standard CP-odd Higgs boson of mass about 10 GeV, introducing a quadratic dependence on the lepton mass in the partial…
Neutrinos and physics beyond the standard model
1997
A brief sketch is made of the present observational status of neutrino physics, with emphasis on the hints that follow from solar and atmospheric neutrino observations, as well as cosmological data on the amplitude of primordial density fluctuations. I also briefly review the ways to account for the observed anomalies and some of their implications.
Exposing dark sector with futureZ-factories
2019
We investigate the prospects of searching dark sector models via exotic [Formula: see text]-boson decay at future [Formula: see text] colliders with Giga [Formula: see text] and Tera [Formula: see text] options. Four general categories of dark sector models: Higgs portal dark matter, vector portal dark matter, inelastic dark matter and axion-like particles, are considered. Focusing on channels motivated by the dark sector models, we carry out a model independent study of the sensitivities of [Formula: see text]-factories in probing exotic decays. The limits on branching ratios of the exotic [Formula: see text] decay are typically [Formula: see text] for the Giga [Formula: see text] and [For…
SU(5)-inspired double beta decay
2015
The short-range part of the neutrinoless double beta amplitude is generated via the exchange of exotic particles, such as charged scalars, leptoquarks and/or diquarks. In order to give a sizable contribution to the total decay rate, the masses of these exotics should be of the order of (at most) a few TeV. Here, we argue that these exotics could be the “light” (i.e., weak-scale) remnants of some B – L violating variants of SU(5). We show that unification of the standard model gauge couplings, consistent with proton decay limits, can be achieved in such a setup without the need to introduce supersymmetry. Since these nonminimal SU(5)-inspired models violate B – L, they generate Majorana neut…