168 research outputs found
Measurement of Mass and Width of the W Boson at LEP
We report on measurements of the mass and total decay width of the W boson
with the L3 detector at LEP. W-pair events produced in
interactions between 161 GeV and 183 GeV centre-of-mass energy are selected in
a data sample corresponding to a total luminosity of 76.7 pb. Combining
all final states in W-pair production, the mass and total decay width of the W
boson are determined to be GeV and
GeV, respectively
Search for Heavy Neutral and Charged Leptons in ee Annihilation at = 183 and 189 GeV
A search for unstable neutral and charged heavy leptons as well as for stable
charged heavy leptons is performed at center-of-mass energies = 183
and 189 GeV with the L3 detector at LEP. No evidence for their existence is
found. We exclude neutral heavy leptons which couple to the electron, muon or
tau family, of the Dirac type for masses below 92.4, 93.3 and 83.3 GeV, and of
the Majorana type for masses below 81.8, 84.1 and 73.5 GeV, respectively. We
exclude unstable charged heavy leptons for masses below 93.9 GeV for a wide
range of the associated neutral heavy lepton mass. If the unstable charged
heavy lepton decays to a light neutrino, we exclude masses below 92.4 GeV. The
production of stable charged heavy leptons with mass less than 93.5 GeV is also
excluded
Measurement of an Elongation of the Pion Source in Z Decays
We measure Bose-Einstein correlations between like-sign charged pion pairs in
hadronic Z decays with the L3 detector at LEP. The analysis is performed in
three dimensions in the longitudinal center-of-mass system. The pion source is
found to be elongated along the thrust axis with a ratio of transverse to
longitudinal radius of
Search for Heavy Isosinglet Neutrinos in ee Annihilation at 130189 GeV
A search for heavy neutrinos that are isosinglets under the standard
gauge group is made at center-of-mass energies 130 189
GeV with the L3 detector at LEP. Such heavy neutrinos are expected in many
extensions of the Standard Model. The search is performed for the first
generation heavy singlet neutrino, , through the decay mode
. We set upper limits on the mixing
parameter between the heavy and light neutrino for the heavy neutrino mass
range from 80 GeV to 185 GeV
Inclusive Sigma+ and Sigma0 Production in Hadronic Z Decays
We report on measurements of the inclusive production rate of Sigma+ and
Sigma0 baryons in hadronic Z decays collected with the L3 detector at LEP. The
Sigma+ baryons are detected through the decay Sigma+ -> p pi0, while the Sigma0
baryons are detected via the decay mode Sigma0 -> Lambda gamma. The average
numbers of Sigma+ and Sigma0 per hadronic Z decay are measured to be: <
N_Sigma+ > + = 0.114 +/- 0.011 (stat) +/- 0.009 (syst), <
N_Sigma0 > + = 0.095 +/- 0.015 (stat) +/- 0.013 (syst). These
rates are found to be higher than the predictions from Monte Carlo
hadronization models and analytical parameterizations of strange baryon
production
Galaxy Clusters Associated with Short GRBs. II. Predictions for the Rate of Short GRBs in Field and Cluster Early-Type Galaxies
We determine the relative rates of short GRBs in cluster and field early-type
galaxies as a function of the age probability distribution of their
progenitors, P(\tau) \propto \tau^n. This analysis takes advantage of the
difference in the growth of stellar mass in clusters and in the field, which
arises from the combined effects of the galaxy stellar mass function, the
early-type fraction, and the dependence of star formation history on mass and
environment. This approach complements the use of the early- to late-type host
galaxy ratio, with the added benefit that the star formation histories of
early-type galaxies are simpler than those of late-type galaxies, and any
systematic differences between progenitors in early- and late-type galaxies are
removed. We find that the ratio varies from R(cluster)/R(field) ~ 0.5 for n =
-2 to ~ 3 for n = 2. Current observations indicate a ratio of about 2,
corresponding to n ~ 0 - 1. This is similar to the value inferred from the
ratio of short GRBs in early- and late-type hosts, but it differs from the
value of n ~ -1 for NS binaries in the Milky Way. We stress that this general
approach can be easily modified with improved knowledge of the effects of
environment and mass on the build-up of stellar mass, as well as the effect of
globular clusters on the short GRB rate. It can also be used to assess the age
distribution of Type Ia supernova progenitors.Comment: ApJ accepted versio
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Measurement of Z0 decays to hadrons, and a precise determination of the number of neutrino species
We have made a precise measurement of the cross section for e+e--->Z0-->hadrons with the L3 detector at LEP, covering the range from 88.28 to 95.04 GeV. From a fit to the Z0 mass, total width, and the hadronic cross section to be MZ0=91.160 +/- 0.024 (experiment) +/-0.030(LEP) GeV, [Gamma]Z0=2.539+/-0.054 GeV, and [sigma]h(MZ0)=29.5+/-0.7 nb. We also used the fit to the Z0 peak cross section and the width todetermine [Gamma]invisible=0.548+/-0.029 GeV, which corresponds to 3.29+/-0.17 species of light neutrinos. The possibility of four or more neutrino flavors is thus ruled out at the 4[sigma] confidence level.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28683/3/0000500.pd
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