Search results for "Lepton"
showing 10 items of 1512 documents
Non-decoupling of Heavy Neutrinos and Lepton Flavour Violation
1995
We consider a class of models predicting new heavy neutral fermionic states, whose mixing with the light neutrinos can be naturally significant and produce observable effects below the threshold for their production. We update the indirect limits on the flavour non-diagonal mixing parameters that can be derived from unitarity, and show that significant rates are in general expected for one-loop-induced rare processes due to the exchange of virtual heavy neutrinos, involving the violation of the muon and electron lepton numbers. In particular, the amplitudes for $\mu$--$e$ conversion in nuclei and for $\mu\to ee^+e^-$ show a non-decoupling quadratic dependence on the heavy neutrino mass $M$,…
Search for CP violation in ZmF ττ
1992
Abstract Using the 18.8 pb−1 of data accumulated at LEP in 1990 and 1991 with the ALEPH detector, a direct test of neutral current CP-invariance is performed by a search for CP-odd correlations in Z decays to τ pairs where both τ decay modes are identified. No evidence for CP-violation is observed. The weak dipole moment of the τ has been measured to be dτ(mZ) = (1.3 ± 1.4 ± 0.1) × 10−17 e·cm which results in an upper limit on the weak dipole moment of |dτ(mZ)| ⩽ 3.7 × 10−17 e·cm with 95% confidence level.
Neutral current couplings of higher generations
1979
Abstract We show that longitudinal polarization of the outgoing lepton in e + e − →μ + (τ + )μ − (τ − ) is expected at the energies of a vector meson resonance (Ψ, ϒ, T, …). On the basis of the standard SU(2) × U(1) theory, this parity violating observable is already appreciable (∼3%) for the ϒ, and it becomes ∼9% for a T at 30 GeV.
Production mechanisms and signatures of isosinglet neutral heavy leptons in Z0 decays
1990
Abstract Neutral Heavy Leptons (NHLs) arise in many extensions of the standard electroweak theory such as superstring inspired models. The possibility of gauge singlets NHLs is especially attractive because it gives an explanation for the observed smallness of the neutrino mass. Existing limits on the possible existence of such particles are still fairly poor. We have investigated isosinglet NHL production and decays within different models. The dominant production cross section is single production (i.e. Z 0 → N + ν or Z 0 → N + ν ) as a result of mixing with the standard doublet neutrinos. Subsequent NHL decays lead to striking signatures. Taking into account the expected luminosities and…
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.
Nuclear cross sections in 16O for β beam neutrinos at intermediate energies
2006
The nuclear cross sections for charged lepton production induced by $\beta$ beam neutrinos (anti-neutrinos) in $^{16}$O have been presented at intermediate energies corresponding to the Lorentz boost factor $\gamma<250 (150)$. The calculations for quasi-elastic lepton production includes the effect of Pauli blocking, Fermi motion and renormalization of weak transition strengths in the nuclear medium. The calculations for the inelastic lepton production is done in the $\Delta$ dominance model. The renormalization of $\Delta$ properties in a nuclear medium and final state interactions of pions with the final nucleus are taken into account. The results may be useful in performing feasibility s…
Charged current neutrino-induced coherent pion production
2007
We analyze the neutrino induced charged current coherent pion production at the energies of interest for recent experiments like K2K and MiniBooNE. Medium effects in the production mechanism and the distortion of the pion wave function, obtained solving the Klein Gordon equation with a microscopic optical potential, are included in the calculation. We find a strong reduction of the cross section due to these effects and also substantial modifications of the energy distributions of the final lepton and pion.
Neutrinoless double beta decay and lepton number violation at the lhc
2013
10.1103/PhysRevD.88.011901
Mesonic and binding contributions to the EMC effect in a relativistic many-body approach
1996
We revise the conventional nuclear effects of Fermi motion, binding and pionic effects in deep inelastic lepton scattering using a relativistic formalism for an interacting Fermi sea and the local density approximation to translate results from nuclear matter to finite nuclei. In addition we also consider effects from rho-meson renormalization in the nucleus. The use of nucleon Green's functions in terms of their spectral functions offers a precise way to account for Fermi motion and binding. On the other hand the use of many body Feynman diagrams in a relativistic framework allows one to avoid using prescriptions given in the past to introduce relativistic corrections in a non relativistic…
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.