Search results for "Standard Model"
showing 10 items of 1206 documents
Search for dark matter in association with a Higgs boson decaying to two photons at s=13 TeV with the ATLAS detector
2017
A search for dark matter in association with a Higgs boson decaying to two photons is presented. This study is based on data collected with the ATLAS detector, corresponding to an integrated lumino ...
Measurement of W-pair production in $e^{+}e^{-}$ collisions at centre-of-mass energies from 183 to 209 GeV
2004
The W + W- production cross section is measured from a data sample corresponding to a total integrated luminosity of 683 pb-1, collected by the ALEPH experiment at LEP at centre-of-mass energies from 183 to 209 GeV. Individual cross sections for the different topologies arising from W decays into leptons or hadrons, as well as the total W-pair cross section are given at eight centre-of-mass energies. The results are found to be in agreement with recently developed Standard Model calculations at the one percent level. The hadronic branching fraction of the W boson is measured to be B(W→qq¯) = 67.13 ± 0.37(stat.) ± 0.15(syst.)%, from which the CKM matrix element |\ensuremathVcs| is determined…
Lepton hadron angular correlations in semileptonic ? decays
1994
We studyT-odd triple momentum correlations in exclusive semileptonic ∋-decays into three pseudoscalar mesons. We define asymmetry ratios that measure theseT-odd correlations and show how to separate the unitarity contribution from the trueCP-violating contributions. TheCP-violating contributions to the asymmetry ratios would have to come from new non-Standard Model sources as theCP-violating Standard Model contributions to the asymmetry ratios are zero. We discuss two extensions of the Standard Model that give rise to nonvanishingCP-violating triple momentum correlations, namely a left-right symmetric model and a multi Higgs boson model. Numerical results on triple momentum correlations are…
Higgs decay into two photons in a warped extra dimension
2014
A detailed five-dimensional calculation of the Higgs-boson decay into two photons is performed in both the minimal and the custodially protected Randall–Sundrum (RS) model, where the Standard Model (SM) fields propagate in the bulk and the scalar sector lives on or near the IR brane. It is explicitly shown that the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$R_\xi $$\end{document}Rξ gauge invariance of the sum of diagrams involving bosonic fields in the SM also applies to the case of these RS scenarios. An e…
Updates to the Dualized Standard Model on Fermion Masses and Mixings
2003
The Dualized Standard Model has scored a number of successes in explaining the fermion mass hierarchy and mixing pattern. This note contains updates to those results including (a) an improved treatment of neutrino oscillation free from previous assumptions on neutrino masses, and hence admitting now the preferred LMA solution to solar neutrinos, (b) an understanding of the limitation of the 1-loop calculation so far performed, thus explaining the two previous discrepancies with data, and (c) an analytic derivation and confirmation of the numerical results previously obtained.
Study of the four-fermion final state at the Z resonance
1995
The process e+e−→, where l is a charged or a neutral lepton and f any charged fermion, is analyzed. The study uses the ALEPH data collected at LEP from 1989 to 1993 at centre-of-mass energies between 88 and 95 GeV, corresponding to almost two million hadronic Z decays and to a total integrated luminosity of 79 pb−1. For all channels, the data agree well with the standard model expectation both in shape and normalization. The indication of an excess in the\(e^ + e^ - \to \tau ^ + \tau ^ - f\bar f\) channel, reported by ALEPH in 1991, is not confirmed.
Constraining New Physics with the Fermilab Measurement ofCPViolation inB→ψKs
1999
Recently, the CDF Collaboration has reported a measurement of the CP asymmetry in the $B\ensuremath{\rightarrow}\ensuremath{\psi}{K}_{s}$ decay: ${a}_{\ensuremath{\psi}{K}_{s}}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.79}_{\ensuremath{-}0.44}^{+0.41}$. We analyze the constraints that follow from this measurement on the size and the phase of contributions from new physics to $B\ensuremath{-}\overline{B}$ mixing. Defining the relative phase between the full ${M}_{12}$ amplitude and the standard model contribution to be $2{\ensuremath{\theta}}_{d}$, we find a new bound: $\mathrm{sin}2{\ensuremath{\theta}}_{d}\ensuremath{\gtrsim}\ensuremath{-}0.6(\ensuremath{-}0.87)$ at $1\ensuremat…
Lepton flavor violation in a Z′ model for the b→s anomalies
2019
In recent years, several observables associated to semileptonic $b \to s$ processes have been found to depart from their predicted values in the Standard Model, including a few tantalizing hints of lepton flavor universality violation. In this work we consider an existing model with a massive $Z^\prime$ boson that addresses the anomalies in $b \to s$ transitions and extend it with a non-trivial embedding of neutrino masses. We analyze lepton flavor violating effects, induced by the non-universal interaction associated to the $b \to s$ anomalies and by the new physics associated to the neutrino mass generation, and determine the expected ranges for the most relevant observables.
Strongly Coupled Models with a Higgs-like Boson
2013
Considering the one-loop calculation of the oblique S and T parameters, we have presented a study of the viability of strongly-coupled scenarios of electroweak symmetry breaking with a light Higgs-like boson. The calculation has been done by using an effective Lagrangian, being short-distance constraints and dispersive relations the main ingredients of the estimation. Contrary to a widely spread believe, we have demonstrated that strongly coupled electroweak models with massive resonances are not in conflict with experimental constraints on these parameters and the recently observed Higgs-like resonance. So there is room for these models, but they are stringently constrained. The vector and…
Vacuum oscillations in the supersymmetric standard model.
1995
We analyze the spectrum and mixing among neutrinos in the minimal supersymmetric standard model with explicit breaking of [ital R] parity. It is shown that (i) the mixing among neutrinos could be large and (ii) the nonzero neutrino mass is constrained to be [le]10[sup [minus]5] eV from arguments based on baryogenesis. Thus vacuum oscillations of neutrinos in this model may offer a solution of the solar neutrino problem. The allowed space of the supersymmetric parameters consistent with this solution is determined.