Search for an Invisibly-Decaying Higgs Boson at LEP

A search for a Higgs boson produced in e^+e^- collisions in association with a Z boson and decaying into invisible particles is performed. Data collected at LEP with the L3 detector at centre-of-mass energies from 189 GeV to 209 GeV are used, corresponding to an integrated luminosity of 0.63/fb. Events with hadrons, electrons or muons with visible masses compatible with a Z boson and missing energy and momentum are selected. They are consistent with the Standard Model expectations. A lower limit of 112.3 GeV is set at 95% confidence level on the mass of the invisibly-decaying Higgs boson in the hypothesis that its production cross section equals that of the Standard Model Higgs boson. Relaxing this hypothesis, upper limits on the production cross section are derived

Generalized event shape and energy flow studies in e+e−e^+ e^- annihilation at s\sqrt{s} = 91.2-208.0 GeV

We present results from a study of hadronic event structure in high energy e(+)e(-') interactions using the L3 detector at LEP. A new class of event shape distributions are measured at and above the Z boson pole for light quark (u, d, s, c) flavours. Energy flow correlations are studied for all hadronic events. Next-to-leading-log QCD calculations and QCD models with improved leading-log approximations are compared to data and good agreement is found at the Z-pole whereas some discrepancies are observed at higher centre-of-mass energies