379 research outputs found
Virtual and Soft Pair Corrections to Polarized Muon Decay Spectrum
Radiative corrections to the muon decay spectrum due to soft and virtual
electron--positron pairs are calculated.Comment: 10pp, 2 PS figs, details of calculations are adde
Left-handed neutrino disappearance probe of neutrino mass and character
We explore the sensitivity to a non vanishing neutrino mass offered by
dynamical observables, i.e., branching ratios and polarizations. The
longitudinal polarization in the C.M. frame decreases by a 4% for and MeV. Taking advantage of the
fact that the polarization is a Lorentz variant quantity, we study the
polarization effects in a boosted frame. By means of a neutrino beam, produced
by a high velocity boosted parent able to flip the neutrino helicity, we find
that an enhanced left-handed neutrino deficit, induced by a Wigner rotation,
appears.Comment: 8 pages and 2 figures. Last version accepted in PRL, new references
and better analysis of experimental possibilitie
Improved limits on nuebar emission from mu+ decay
We investigated mu+ decays at rest produced at the ISIS beam stop target.
Lepton flavor (LF) conservation has been tested by searching for \nueb via the
detection reaction p(\nueb,e+)n. No \nueb signal from LF violating mu+ decays
was identified. We extract upper limits of the branching ratio for the LF
violating decay mu+ -> e+ \nueb \nu compared to the Standard Model (SM) mu+ ->
e+ nue numub decay: BR < 0.9(1.7)x10^{-3} (90%CL) depending on the spectral
distribution of \nueb characterized by the Michel parameter rho=0.75 (0.0).
These results improve earlier limits by one order of magnitude and restrict
extensions of the SM in which \nueb emission from mu+ decay is allowed with
considerable strength. The decay \mupdeb as source for the \nueb signal
observed in the LSND experiment can be excluded.Comment: 10 pages, including 1 figure, 1 tabl
P and T Odd Asymmetries in Lepton Flavor Violating Tau Decays
We calculated the differential cross sections of the processes in which one
of the pair created tau particles at an e^+ e^- collider decays into lepton
flavor violating final states e.g. tau -> mu gamma, tau -> 3 mu, tau -> mu ee.
Using the correlations between angular distributions of both sides of tau
decays, we can obtain information on parity and CP violations of lepton flavor
non-conserving interactions. The formulae derived here are useful in
distinguishing different models, since each model of physics beyond the
standard model predicts different angular correlations. We also calculate
angular distributions of the major background process to tau -> l gamma search,
namely tau -> l nu \bar{\nu} gamma, and discuss usefulness of the angular
correlation for background suppression.Comment: 31 pages, 5 figure
Search for the Lepton Number Violating Process nu_mu-bar e^- -> mu^- nu_e-bar
The NuTeV experiment at Fermilab has used a sign-selected neutrino beam to
perform a search for the lepton number violating process nu_mu-bar e^- -> mu^-
nu_e-bar, and to measure the cross-section of the Standard Model inverse muon
decay process nu_mu e^- -> mu^- nu_e. NuTeV measures the inverse muon decay
asymptotic cross-section sigma/E to be 13.8 +/- 1.2 +/- 1.4 x 10^-42 cm^2/GeV.
The experiment also observes no evidence for lepton number violation and places
one of the most restrictive limits on the LNV/IMD cross-section ratio at < 1.7%
at 90% C.L. for V-A couplings and < 0.6% for scalar couplings.Comment: 4 pages, 4 figures, 2 tables. Submitted to Physics Review Letter
Signals of extra gauge bosons and exotic leptons in SU(6)U(1)
We study some of the consequences of the SU(6)U(1) model
of unification of electroweak interactions and families with a horizontal gauge
group SU(2), paying special attention to processes with flavor changing
neutral currents. We compute at tree level the decays , and from which we obtain lower bounds
for the mass of the horizontal gauge boson associated with FCNC. Finally we
obtain limits on the mixing between ordinary and exotic charged leptons
Annihilation-in-flight of polarised positrons with polarised electrons as an analyser of the positron polarisation from muon decay
Tests of the Equivalence Principle with Neutral Kaons
We test the Principle of Equivalence for particles and antiparticles, using
CPLEAR data on tagged K0 and K0bar decays into pi^+ pi^-. For the first time,
we search for possible annual, monthly and diurnal modulations of the
observables |eta_{+-}| and phi_{+-}, that could be correlated with variations
in astrophysical potentials. Within the accuracy of CPLEAR, the measured values
of |eta_{+-}| and phi_{+-} are found not to be correlated with changes of the
gravitational potential. We analyze data assuming effective scalar, vector and
tensor interactions, and we conclude that the Principle of Equivalence between
particles and antiparticles holds to a level of 6.5, 4.3 and 1.8 x 10^{-9},
respectively, for scalar, vector and tensor potentials originating from the Sun
with a range much greater than the distance Earth-Sun. We also study
energy-dependent effects that might arise from vector or tensor interactions.
Finally, we compile upper limits on the gravitational coupling difference
between K0 and K0bar as a function of the scalar, vector and tensor interaction
range.Comment: 15 pages latex 2e, five figures, one style file (cernart.csl)
incorporate
Test of CPT Symmetry and Quantum Mechanics with Experimental data from CPLEAR
We use fits to recent published CPLEAR data on neutral kaon decays to
and to constrain the CPT--violation parameters
appearing in a formulation of the neutral kaon system as an open
quantum-mechanical system. The obtained upper limits of the CPT--violation
parameters are approaching the range suggested by certain ideas concerning
quantum gravity.Comment: 9 pages of uuencoded postscript (includes 3 figures
Tau Neutrino Helicity from Energy Correlations
We report a measurement of the magnitude of the tau neutrino helicity from
tau-pair events taken with the CLEO detector at the CESR electron-positron
storage ring. Events in which each tau undergoes the decay tau -> h nu, with h
a charged pion or kaon, are analyzed for energy correlations between the
daughter hadrons, yielding |xi| = 2*|h_nu| = 1.03 +/- 0.06 +/- 0.04, with the
first error statistical and the second systematic.Comment: 11 pages, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
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