Search results for "Lepton"
showing 10 items of 1512 documents
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.
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.
Search forZZandZγ*Production inpp¯Collisions ats=1.96 TeVand Limits on AnomalousZZZandZZγ*Couplings
2008
We present a study of mu mu mu mu, eeee, and mu mu ee events using 1 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron p (p) over bar Collider at root s = 1.96 TeV. Requiring t ...
Weak Interactions and Solar Neutrinos: Testing the Oscillation Hypothesis
1988
Various proposals for understanding the reduced solar neutrino flux in terms of non-standard neutrino propagation properties are briefly reviewed in the context of weak interaction theory. Emphasis is given to neutrino oscillation models which may be tested experimentally, despite the small mass parameter involved. Spontaneous lepton number (and R parity) breaking in supergravity — the supersymmetric doublet Majoron model — solves the solar neutrino problem through matter-enhanced neutrino oscillations. The spectrum of supersymmetric particles is restricted in a way that will be probed by high energy collider experiments. In addition, low energy processes associated with the existence of th…
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.
Universality-Breaking Effects in Leptonic Z Decays
1993
We analyze the possibility of universality violation in diagonal leptonic decays of the $Z$ boson, in the context of interfamily "see-saw" models. In a minimal extension of the Standard Model with right-handed neutrino fields, we find that universality-breaking effects increase quadratically with the heavy Majorana neutrino mass and may be observed in the running $LEP$ experiments.
Beam-Helicity Asymmetries in Double-Pion Photoproduction off the Proton
2009
Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz in the three isospin channels $\vec{\gamma}p\to \pi^{+}\pi^0n$, $\vec{\gamma}p\to \pi^{0}\pi^0p$ and $\vec{\gamma}p\to \pi^{+}\pi^{-}p$ . The circularly polarized photons, produced from bremsstrahlung of longitudinally polarized electrons, were tagged with the Glasgow magnetic spectrometer. Charged pions and the decay photons of $\pi^0$ mesons were detected in a $~4\pi$ electromagnetic calorimeter which combined the Crystal Ball detector with the TAPS detector. The precisely measured asymmetries are very sensitive to details of the production processes and are thus key observables in the modeling of the reaction d…
Physical observables in the decay Λb→Λc(→Λ+π)+τ−+ν̄τ
2015
We analyze the tauonic semileptonic baryon decays [Formula: see text] with particular emphasis on the lepton helicity flip contributions which vanish for zero lepton masses. We calculate the total rate, differential decay distributions, the longitudinal and transverse polarization components of the [Formula: see text] and the [Formula: see text], and the lepton-side forward-backward asymmetries. We use the covariant confined quark model to provide numerical results on these observables.
Unexplained Excess of Electronlike Events from a 1-GeV Neutrino Beam
2009
The MiniBooNE Collaboration observes unexplained electronlike events in the reconstructed neutrino energy range from 200 to 475 MeV. With 6.46 x 10(20) protons on target, 544 electronlike events are observed in this energy range, compared to an expectation of 415.2 +/- 43.4 events, corresponding to an excess of 128.8 +/- 20.4 +/- 38.3 events. The shape of the excess in several kinematic variables is consistent with being due to either nu(e) and (nu) over bar (e) charged-current scattering or nu(mu) neutral-current scattering with a photon in the final state. No significant excess of events is observed in the reconstructed neutrino energy range from 475 to 1250 MeV, where 408 events are obse…
Hints ofθ13>0from Global Neutrino Data Analysis
2008
Nailing down the unknown neutrino mixing angle theta{13} is one of the most important goals in current lepton physics. In this context, we perform a global analysis of neutrino oscillation data, focusing on theta{13}, and including recent results [ (unpublished)]. We discuss two converging hints of theta{13}>0, each at the level of approximately 1sigma: an older one coming from atmospheric neutrino data, and a newer one coming from the combination of solar and long-baseline reactor neutrino data. Their combination provides the global estimate sin{2}theta{13}=0.016+/-0.010(1sigma), implying a preference for theta{13}>0 with non-negligible statistical significance ( approximately 90% C.L.). W…