158 research outputs found
Measurement of W Polarisation at LEP
The three different helicity states of W bosons produced in the reaction e+
e- -> W+ W- -> l nu q q~ at LEP are studied using leptonic and hadronic W
decays. Data at centre-of-mass energies \sqrt s = 183-209 GeV are used to
measure the polarisation of W bosons, and its dependence on the W boson
production angle. The fraction of longitudinally polarised W bosons is measured
to be 0.218 \pm 0.027 \pm 0.016 where the first uncertainty is statistical and
the second systematic, in agreement with the Standard Model expectation
Search for Anomalous Couplings in the Higgs Sector at LEP
Anomalous couplings of the Higgs boson are searched for through the processes
e^+ e^- -> H gamma, e^+ e^- -> e^+ e^- H and e^+ e^- -> HZ. The mass range 70
GeV < m_H < 190 GeV is explored using 602 pb^-1 of integrated luminosity
collected with the L3 detector at LEP at centre-of-mass energies
sqrt(s)=189-209 GeV. The Higgs decay channels H -> ffbar, H -> gamma gamma, H
-> Z\gamma and H -> WW^(*) are considered and no evidence is found for
anomalous Higgs production or decay. Limits on the anomalous couplings d, db,
Delta(g1z), Delta(kappa_gamma) and xi^2 are derived as well as limits on the H
-> gamma gamma and H -> Z gamma decay rates
Measurement of W Polarisation at LEP
The three different helicity states of W bosons produced in the reaction e+
e- -> W+ W- -> l nu q q~ at LEP are studied using leptonic and hadronic W
decays. Data at centre-of-mass energies \sqrt s = 183-209 GeV are used to
measure the polarisation of W bosons, and its dependence on the W boson
production angle. The fraction of longitudinally polarised W bosons is measured
to be 0.218 \pm 0.027 \pm 0.016 where the first uncertainty is statistical and
the second systematic, in agreement with the Standard Model expectation
Bose-Einstein Correlations of Neutral and Charged Pions in Hadronic Z Decays
Bose-Einstein correlations of both neutral and like-sign charged pion pairs
are measured in a sample of 2 million hadronic Z decays collected with the L3
detector at LEP. The analysis is performed in the four-momentum difference
range 300 MeV < Q < 2 GeV. The radius of the neutral pion source is found to be
smaller than that of charged pions. This result is in qualitative agreement
with the string fragmentation model
Z Boson Pair-Production at LEP
Events stemming from the pair-production of Z bosons in e^+e^- collisions are
studied using 217.4 pb^-1 of data collected with the L3 detector at
centre-of-mass energies from 200 GeV up to 209 GeV. The special case of events
with b quarks is also investigated.
Combining these events with those collected at lower centre-of-mass energies,
the Standard Model predictions for the production mechanism are verified. In
addition, limits are set on anomalous couplings of neutral gauge bosons and on
effects of extra space dimensions
Study of the e+e- -> Ze+e- process at LEP
The cross section of the process e+e- -> Ze+e is measured with 0.7fb^-1 of
data collected with the L3 detector at LEP. Decays of the Z boson into quarks
and muons are considered at centre-of-mass energies ranging from 183GeV up to
209GeV. The measurements are found to agree with Standard Model predictions,
achieving a precision of about 10% for the hadronic channel
Inclusive Lambda Production in Two-Photon Collisions at LEP
The reactions e^+e^- -> e^+e^- Lambda X and e^+e^- -> e^+e^- Lambda X are
studied using data collected at LEP with the L3 detector at centre-of-mass
energies between 189 and 209 GeV. Inclusive differential cross sections are
measured as a function of the lambda transverse momentum, p_t, and
pseudo-rapidity, eta, in the ranges 0.4 GeV < p_t < 2.5 GeV and |\eta| < 1.2.
The data are compared to Monte Carlo predictions. The differential cross
section as a function of p_t is well described by an exponential of the form A
exp (- p_t / )$
Lambda and Sigma0 Pair Production in Two-Photon Collisions at LEP
Strange baryon pair production in two-photon collisions is studied with the
L3 detector at LEP. The analysis is based on data collected at e+e-
centre-of-mass energies from 91 GeV to 208 GeV, corresponding to an integrated
luminosity of 844 pb-1. The processes gamma gamma -> Lambda Anti-lambda and
gamma gamma -> Sigma0 Anti-sigma0 are identified. Their cross sections as a
function of the gamma gamma centre-of-mass energy are measured and results are
compared to predictions of the quark-diquark model
Search for Charged Higgs Bosons at LEP
A search for pair-produced charged Higgs bosons is performed with the L3
detector at LEP using data collected at centre-of-mass energies between 189 and
209GeV, corresponding to an integrated luminosity of 629.4/pb. Decays into a
charm and a strange quark or into a tau lepton and its neutrino are considered.
No significant excess is observed and lower limits on the mass of the charged
Higgs boson are derived at the 95% confidence level. They vary from 76.5 to
82.7GeV, as a function of the H->tv branching ratio
Search for Colour Singlet and Colour Reconnection Effects in Hadronic Z Decays at LEP
A search is performed in symmetric 3-jet hadronic Z decay events for evidence
of colour singlet production or colour reconnection effects. Asymmetries in the
angular separation of particles are found to be sensitive indicators of such
effects. Upper limits on the level of colour singlet production and colour
reconnection effects are established for a variety of models
- …