Search results for "Lepton"
showing 10 items of 1512 documents
LeptonicCPasymmetries in flavor-changingH0decays
1993
Leptonic flavor-changing ${H}^{0}$ decays with branching ratios of the order of ${10}^{\ensuremath{-}5}$-${10}^{\ensuremath{-}6}$ may constitute an interesting framework when looking for large $\mathrm{CP}$-violating effects. We show that leptonic $\mathrm{CP}$ asymmetries of an intermediate ${H}^{0}$ boson can be fairly large in natural scenarios of the minimal standard model with right-handed neutrinos, at a level that may be probed at future ${H}^{0}$ factories.
First Measurement of the Absolute Branching Fraction of Λ→pμ−ν¯μ
2021
The absolute branching fraction of Λ→pμ−ν¯μ is reported for the first time based on an e+e− annihilation sample of 10×109 J/ψ events collected with the BESIII detector at s=3.097 GeV. The branching fraction is determined to be B(Λ→pμ−ν¯μ)=[1.48±0.21(stat)±0.08(syst)]×10−4, which is improved by about 30% in precision over the previous indirect measurements. Combining this result with the world average of B(Λ→pe−ν¯e), we obtain the ratio {[Γ(Λ→pμ−ν¯μ)]/[Γ(Λ→pe−ν¯e)]} to be 0.178±0.028, which agrees with the standard model prediction assuming lepton flavor universality. The asymmetry of the branching fractions of Λ→pμ−ν¯μ and Λ¯→p¯μ+νμ is also determined, and no evidence for CP violation is fo…
Lepton mass effects for beam-normal single-spin asymmetry in elastic muon-proton scattering
2019
We estimate the beam-normal single-spin asymmetry in elastic lepton-proton scattering without employing the ultrarelativistic approximation. Our calculation is relevant for analyses of muon scattering at energies of few hundred MeV and below -- when effects of the muon mass become essential. At such energies, the transverse polarization of the muon beam is expected to contribute significantly to the systematic uncertainty of precision measurements of elastic muon-proton scattering. We evaluate such systematics using an example of the MUSE experiment at PSI. The muon asymmetry is estimated at about 0.1\% in kinematics of MUSE and it is the largest for scattering into a backward hemisphere.
Performance of the large scale HV-CMOS pixel sensor MuPix8
2019
The Mu3e experiment is searching for the charged lepton flavour violating decay $ ��^+\rightarrow e^+ e^- e^+ $, aiming for an ultimate sensitivity of one in $10^{16}$ decays. In an environment of up to $10^9$ muon decays per second the detector needs to provide precise vertex, time and momentum information to suppress accidental and physics background. The detector consists of cylindrical layers of $50\, ��\text{m}$ thin High Voltage Monolithic Active Pixel Sensors (HV-MAPS) placed in a $1\,\text{T}$ magnetic field. The measurement of the trajectories of the decay particles allows for a precise vertex and momentum reconstruction. Additional layers of fast scintillating fibre and tile detec…
Searches for the decaysB0→l±τ∓andB+→l+ν(l=e,μ) using hadronic tag reconstruction
2008
We present searches for the leptonic decays B{sup +} {yields} {ell}{sup +}{nu} and the lepton flavor violating decays B{sup 0} {yields} {ell}{sup {+-}}{tau}{sup {-+}}, where {ell} = e, {mu}, with data collected by the BABAR experiment at SLAC. This search demonstrates a novel technique in which we fully reconstruct the accompanying {bar B} in {Upsilon}(4S) {yields} B{bar B} events, and look for a monoenergetic lepton from the signal B decay. The signal yield is extracted from a fit to the signal lepton candidate momentum distribution in the signal B rest frame. Using a data sample of approximately 378 million B{bar B} pairs (342 fb{sup -1}), we find no evidence of signal in any of the decay…
Electron-capture branch ofTc100and tests of nuclear wave functions for double-βdecays
2008
We present a measurement of the electron-capture branch of $^{100}\mathrm{Tc}$. Our value, $B(\mathrm{EC})=(2.6\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$, implies that the $^{100}\mathrm{Mo}$ neutrino absorption cross section to the ground state of $^{100}\mathrm{Tc}$ is roughly 50% larger than previously thought. Disagreement between the experimental value and QRPA calculations relevant to double-$\ensuremath{\beta}$ decay matrix elements persists. We find agreement with previous measurements of the 539.5- and 590.8-keV $\ensuremath{\gamma}$-ray intensities.
Anomalies in b→s Transitions and Dark Matter
2018
Since 2013, the LHCb collaboration has reported on the measurement of several observables associated to $b \to s$ transitions, finding various deviations from their predicted values in the Standard Model. These include a set of deviations in branching ratios and angular observables, as well as in the observables $R_K$ and $R_{K^\ast}$, specially built to test the possible violation of Lepton Flavor Universality. Even though these tantalizing hints are not conclusive yet, the $b \to s$ anomalies have gained considerable attention in the flavor community. Here we review New Physics models that address these anomalies and explore their possible connection to the dark matter of the Universe. Af…
Cosmic ray physics with the ALEPH detector
2000
Abstract ALEPH is one of the four detectors at the Large Electron–Positron Collider (LEP) at a depth of about 320 m.w.e. Its hadron calorimeter and scintillator arrays installed at distances up to about 1 km away from ALEPH are used to measure cosmic muon induced time coincidences over large distances. The aim of this experiment (CosmoALEPH) is (1) to study the muon component above 70 GeV of Extensive Air Showers (EAS) and (2) to test the feasibility of searching for time correlations over even larger distances (up to 8 km) between the four LEP detectors. Layout and first results of CosmoALEPH are presented demonstrating the potential for cosmic ray physics in the LEP tunnel. The multiplici…
Updated measurement of the average b hadron lifetime
1992
An improved measurement of the average lifetime of b hadrons has been performed with the ALEPH detector. From a sample of 260000 hadronic Z0 decays, recorded during the 1991 LEP run with the silicon vertex detector fully operational, a fit to the impact parameter distribution of lepton tracks coming from semileptonic decays yields an average b hadron lifetime of 1.49 +/- 0.03 +/- 0.06 ps.
A measurement of the b baryon lifetime
1992
In 451 000 hadronic Z0 decays, recorded with the ALEPH detector at LEP, the yields of lambdal- and lambdal+ combinations are measured. Semileptonic decays of b baryons result in a signal of 122 +/- 18(stat.)+22/-23(syst.) lambdal- combinations. From a fit to the impact parameter distribution of the leptons in the lambdal- sample, the lifetime of b baryons is measured to be 1.12+0.32/-0.29(stat.) +/- 0.16(syst.) ps.