Search results for "Lepton"
showing 10 items of 1512 documents
A4-based tri-bimaximal mixing within inverse and linear seesaw schemes
2009
We consider tri-bimaximal lepton mixing within low-scale seesaw schemes where light neutrino masses arise from TeV scale physics, potentially accessible at the Large Hadron Collider (LHC). Two examples are considered, based on the A4 flavor symmetry realized within the inverse or the linear seesaw mechanisms. Both are highly predictive so that in both the light neutrino sector effectively depends only on three mass parameters and one Majorana phase, with no CP violation in neutrino oscillations. We find that the linear seesaw leads to a lower bound for neutrinoless double beta decay while the inverse seesaw does not. The models also lead to potentially sizeable decay rates for lepton flavor…
MEASUREMENT OF THE TAU-POLARIZATION AT THE Z-RESONANCE
1993
Using 18.8 pb-1 of data collected in 1990 and 1991, ALEPH has measured the tau polarisation in the decay modes tau-->enunuBAR, tau-->mununuBAR, tau-->rhonu tau-->a1nu, using both the individual tau decay kinematics and the event acollinearity. The measurement of the tau polarisation as a function of the production polar angle yields the two parameters A(tau) and A(e), where A(l) = 2g(V)l g(A)l/[(g(V)l)2 + (g(A)l)2]. The results A(tau) = 0.143 +/- 0.023 and A(e) = 0. 120 +/- 0.026 are consistent with the hypothesis of electron-tau universality. Assuming universality yields a measurement of the effective weak mixing angle sin 2theta(W)eff = 0.2332 +/- 0.0022.
A CMB search for the neutrino mass mechanism and its relation to the Hubble tension
2020
AbstractThe majoron, a pseudo-Goldstone boson arising from the spontaneous breaking of global lepton number, is a generic feature of many models intended to explain the origin of the small neutrino masses. In this work, we investigate potential imprints in the cosmic microwave background (CMB) arising from massive majorons, should they thermalize with neutrinos after Big Bang Nucleosynthesis via inverse neutrino decays. We show that measurements of the CMB are currently sensitive to neutrino-majoron couplings as small as $$\lambda \sim 10^{-13}$$λ∼10-13, which if interpreted in the context of the type-I seesaw mechanism correspond to a lepton number symmetry breaking scale $$v_L \sim {\math…
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…
Search for $B^0_s-\overline{B^0_s}$ oscillations and a measurement of $B^0_d-\overline{B^0_d}$ oscillations using events with an inclusively reconstr…
2003
Neutral B meson oscillations in the B-s(0) - , and B-d(0) - systems were studied using a sample of about 4.0 million hadronic Z decays recorded by the DELPHI detector between 1992 and 2000. Events with a high transverse momentum lepton were removed and a sample of 770 k events with an inclusively reconstructed vertex was selected. The mass difference between the two physical states in the B-d(0) - system was measured to be: Deltam(d) = (0.531 +/- 0.025(stat.) +/- 0.007(syst.))ps(-1). The following limit on the width difference of these states was also obtained: DeltaGamma(Bd)/Gamma(Bd) oscillations was found, a limit on the mass difference of the two physical states was given:, Deltam(s) > …
Automated NNLL+NLO Resummation for Jet-Veto Cross Sections
2014
In electroweak-boson production processes with a jet veto, higher-order corrections are enhanced by logarithms of the veto scale over the invariant mass of the boson system. In this paper, we resum these Sudakov logarithms at next-to-next-to-leading logarithmic (NNLL) accuracy and match our predictions to next-to-leading order (NLO) fixed-order results. We perform the calculation in an automated way, for arbitrary electroweak final states and in the presence of kinematic cuts on the leptons produced in the decays of the electroweak bosons. The resummation is based on a factorization theorem for the cross sections into hard functions, which encode the virtual corrections to the boson product…
MEASUREMENT OF TAU BRANCHING RATIOS
1992
著者人数：112名
Joint angular decay distributions in exclusive weak decays of heavy mesons and baryons
1993
We present the results of a comprehensive analysis of the angular decay distributions occurring in the weak exclusive decays of the lowest lying charm and bottom mesons and baryons. We deal with both semileptonic and nonleptonic decays and discuss various decay channels and their subsequent cascade decay chains including lepton mass effects. In the case of baryons we include polarization effects for the parent charm or bottom baryon. We list in table form general formulae which allow one to write down the joint angular decay distributions for the cascade decaysA→B(→b 1+...+b n )+C(→c 1+...+c n ), for all spin casess A ≤1/2 ands B ,s C ≤3/2 for the prominent decays ofB andC. Two examples inv…
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…
Electroweak interaction in muonic atoms
1992
The parity non-conserving effective neutral current interaction between charged leptons and nucleons is studied in its implications for atomic physics. Present results on heavy electronic atoms are discussed within the standard electroweak theory and beyond. The new features provided by muonic atoms open the way to the nuclear-spin-dependent parity non-conserving effects. Different observables proposed to study these effects in muonic atoms are reviewed.