Aims.Several experiments have reported observations on possible correlations between the flux of high energy muons and intense solar flares. If confirmed, these observations would have significant ...implications for acceleration processes in the heliosphere able to accelerate protons and other ions to energies of at least tens of GeV. Methods: .The solar flare of the 14 of July 2000 offered a unique opportunity for the L3+C experiment to search for a correlated enhancement in the flux of muons using the L3 precision muon spectrometer. Its capabilities for observing a directional excess in the flux of muons above 15 GeV (corresponding to primary proton energies above 40 GeV) are presented along with observations made on the 14th of July 2000. Results: .We report an excess which appeared at a time coincident with the peak increase of solar protons observed at lower energies. The probability that the excess is a background fluctuation is estimated to be 1%. No similar excess of the muon flux was observed up to 1.5 h after the solar flare time.
Hadron production and lepton-pair production in e+e- collisions are studied with data collected with the L3 detector at LEP at centre-of-mass energies sqrt{s}=192-208GeV. Using a total integrated ...luminosity of 453/pb, 36057 hadronic events and 12863 lepton-pair events are selected. The cross sections for hadron production and lepton-pair production are measured for the full sample and for events where no high-energy initial-state-radiation photon is emitted prior to the collisions. Lepton-pair events are further investigated and forward-backward asymmetries are measured. Finally, the differential cross sections for electron-positron pair-production is determined as a function of the scattering angle. An overall good agreement is found with Standard Model predictions.
Exclusive ρ+ρ− production in two-photon collisions between a quasi-real photon, γ, and a mid-virtuality photon, γ∗, is studied with data collected at LEP at centre-of-mass energies 183 GeV⩽s⩽209 GeV ...with a total integrated luminosity of 684.8 pb−1. The cross section of the γγ∗→ρ+ρ− process is determined as a function of the photon virtuality, Q2, and the two-photon centre-of-mass energy, Wγγ, in the kinematic region: 0.2 GeV2⩽Q2⩽0.85 GeV2 and 1.1 GeV⩽Wγγ⩽3 GeV. These results, together with previous L3 measurements of ρ0ρ0 and ρ+ρ− production, allow a study of the γγ∗→ρρ process over the Q2-region 0.2 GeV2⩽Q2⩽30 GeV2.
Exclusive ρ0ρ0 production in two-photon collisions between a quasi-real and a mid-virtuality photon is studied with data collected at LEP at centre-of-mass energies 183<s<209 GeV with a total ...integrated luminosity of 684.8 pb−1. The cross section of the process γγ*→ρ0ρ0 is determined as a function of the photon virtuality, Q2, and the two-photon centre-of-mass energy, Wγγ, in the kinematic region: 0.2<Q2<0.85 GeV2 and 1.1<Wγγ<3 GeV.
Exclusive ρ+ρ− production in two-photon collisions involving a single highly-virtual photon is studied for the first time with data collected by the L3 experiment at LEP at centre-of-mass energies ...89<s<209GeV with a total integrated luminosity of 854.7 pb−1. The cross section of the process γγ*→ρ+ρ− is determined as a function of the photon virtuality, Q2, and the two-photon centre-of-mass energy, Wγγ, in the kinematic region: 1.2<Q2<30GeV2 and 1.1<Wγγ<3GeV. The ρ+ρ− production cross section is found to be of the same magnitude as the cross section of the process γγ*→ρ0ρ0, measured in the same kinematic region by L3, and to have similar Wγγ and Q2 dependences.
In this Report, QCD results obtained from a study of hadronic event structure in high energy e^+e^- interactions with the L3 detector are presented. The operation of the LEP collider at many ...different collision energies from 91 GeV to 209 GeV offers a unique opportunity to test QCD by measuring the energy dependence of different observables. The main results concern the measurement of the strong coupling constant, \alpha_s, from hadronic event shapes and the study of effects of soft gluon coherence through charged particle multiplicity and momentum distributions.
The charged-particle multiplicity distribution is measured for all hadronic events as well as for light-quark and b-quark events produced in e+e− collisions at the Z pole. Moments of the ...charged-particle multiplicity distributions are calculated. The Hq moments of the multiplicity distributions are studied, and their quasi-oscillations as a function of the rank of the moment are investigated.
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