Search results for "Standard Model"
showing 10 items of 1206 documents
Coherent muon-electron conversion in the dualized standard model
2000
Muon-electron conversion in nuclei is considered in the framework of the Dualized Standard Model. The ratio $B_{\mu-e}$ of the conversion rate to the total muon capture rate is derived, and computed for several nuclei in a parameter-free calculation using parameters previously determined in different physical contexts. The values obtained all lie within the present experimental bounds, but some are so close as to seem readily accessible to experiments already being planned. Similar considerations are applied also to muon-electron conversion in muonium but give rates many orders of magnitude below the present experiment limit.
Measurement of σ(pp¯→Z+X)Br(Z→τ+τ−) at s=1.96 TeV
2009
We present a measurement of the cross section for Z boson production times the branching fraction to tau lepton pairs sigma(p (p) over bar -> Z + X)Br(Z -> tau(+)tau(-)) in p (p) over bar collisions at root s = 1.96 TeV. The measurement is performed in the channel in which one tau lepton decays into a muon and neutrinos. and the other tau lepton decays hadronically or into an electron and neutrinos. The data sample corresponds to an integrated luminosity of 1.0 fb(-1) collected with the DO detector at the Fermilab Tevatron Collider. The sample contains 1511 candidate events with an estimated 20% background from jets or muons misidentified as tau leptons. We obtain sigma . Br = 240 +/- 8 (st…
Measurement of the W±Z production cross section and limits on anomalous triple gauge couplings in proton–proton collisions at s=7 TeV with the ATLAS …
2012
This Letter presents a measurement of W(+/-)Z production in 1.02 fb(-1) of pp collision data at root s = 7 TeV collected by the ATLAS experiment in 2011. Doubly leptonic decay events are selected w ...
LAB observables for the muon polarization in K+->pi(+)mu(+)mu(-)
1999
We analyse the muon longitudinal polarization asymmetry \Delta_long in the decay K^+ --> \pi^+ \mu^+ mu^-. It is stressed that, since the muon helicities are not Lorentz-invariant quantities, the magnitude of \Delta_long depends in general on the reference frame. We consider the muon helicities in the LAB system, and study the sensitivity of the longitudinal polarization asymmetry to the flavour-mixing parameters in the Standard Model for stopped and in-flight decaying K^+. A similar analysis is carried out for the decay K_L --> \mu^+ \mu^-. We find that in both cases the asymmetry is diluted when increasing the energy of the decaying kaons.
IMPROVED BOUNDS ON THE TAU MAGNETIC MOMENTS
2001
New limits on the tau magnetic couplings to the photon, the Z and the W bosons are obtained from the most general effective Lagrangian. Model independent bounds are set using data for tau pair production and W decay into tau leptons at LEP1, LEP2, SLD and hadron colliders. For the anomalous magnetic moment the bounds are, for the first time, of the order of magnitude of the standard model prediction.
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.
A new limit on the CP violating decay KS→3π0 with the KLOE experiment
2013
We have carried out a new direct search for the CP violating decay K-S -> 3 pi(0) with 1.7 fb(-1) of e(+)e(-) collisions collected by the KLOE detector at the Phi-factory DA Phi NE. We have searched for this decay in a sample of about 5.9 x 10(8) KSKL events tagging the K-S by means of the K-L interaction in the calorimeter and requiring six prompt photons. With respect to our previous search, the analysis has been improved by increasing of a factor four the tagged sample and by a more effective background rejection of fake K-S tags and spurious clusters. We find no candidates in data and simulated background samples, while we expect 0.12 standard model events. Normalizing to the number of …