We report on the observation of single W boson production in a data sample collected by the L3 detector at LEP2. The signal consists of large missing energy final states with a single energetic lepton or two hadronic jets. The cross-section is measured to be 0.61 −0.33 +0.43 ± 0.05 pb at the centre of mass energy s = 172 GeV , consistent with the Standard Model expectation. From this measurement the following limits on the anomalo γWW gauge couplingsare derived at 95% CL: −3.6 < Δκ γ < 1.5 and −3.6 < λ γ < 3.6.

We report on the measurement of W-boson pair-production with the L3 detector at LEP at a centre-of-mass energy of 161.34 GeV. In a data sample corresponding to a total luminosity of 11 pb −1 , we select four-fermion events with high invariant masses of pairs of hadronic jets or leptons. Combining all final states, the measured total cross section for W-pair production is: sigma WW = 2.89 −0.70 +0.81 (stat.) ± 0.14 (syst.) pb. Within the Standard Model, this corresponds to a mass of the W boson of: M W = 80.80 −0.42 +0.48 (exp.) ± 0.03 (LEP) GeV. Limits on anomalous triple-vector-boson couplings are derived.

In June 1996, the LEP centre-of-mass energy was raised to 161 GeV. Pair production of W bosons in e + e − collisions was observed for the first time by the LEP experiments. An integrated luminosity of 11 pb −1 was recorded in the ALEPH detector, in which WW candidate events were observed. In 6 events both Ws decay leptonically. In 16 events, one W decays leptonically, the other into hadrons. In the channel where both Ws decay into hadrons, a signal was separated from the large background by means of several multi-variate analyses. The W pair cross-section is measured to be σ WW = 4.23 ± 0.73 (stat.) ± 0.19 (syst.) pb. From this cross-section, the W mass is derived within the framework of the Standard Model: m W = 80.14 ± 0.34 (stat.) ± 0.09 (syst.) ± 0.03 (LEP energy) GeV/ c 2

The total cross section and the forward-backward asymmetry for the process e + e − → μ + μ − ( nγ ) are measured in the energy range 20–136 GeV by reconstructing the effective centre-of-mass energy after initial state radiation. The analysis is based on the data recorded with the ALEPH detector at LEP between 1990 and 1995, corresponding to a total integrated luminosity of 143.5 pb −1 . Two different approaches are used: in the first one an exclusive selection of events with hard initial state radiation in the energy range 20–88 GeV is directly compared with the Standard Model predictions showing good agreement. In the second one, all events are used to obtain a precise measurement of the energy dependence of σ 0 and A FB 0 from a model independent fit, enabling constraints to be placed on models with extra Z bosons.

Hadronic and leptonic cross-sections and forward-backward asymmetries are measured using 5.7 pb −1 of data taken with the ALEPH detector at LEP at centre-of-mass energies of 130 and 136 GeV. The results agree with Standard Model expectations. The measurement of hadronic cross-sections far away from the Z resonance improves the determination of the interference between photon and Z exchange. Constraints on models with extra Z bosons are presented.

We report on the first measurements of e + e − annihilations into hadrons and lepton pairs at centre-of-mass energies between 130 GeV and 140 GeV. In a total luminosity of 5 pb −1 collected with the L3 detector at LEP we select 1577 hadronic and 401 lepton-pair events. The measured cross sections and leptonic forward-backward asymmetries agree well with the Standard Model predictions.

Four-fermion events have been selected in a data sample of 5.8 pb −1 collected with the aleph detector at centre-of-mass energies of 130 and 136 GeV. The final states ℓ + ℓ − q q , ℓ + ℓ − ℓ + ℓ − , ν ν q q , and ν ν ℓ + ℓ − have been examined. Five events are observed in the data, in agreement with the Standard Model predictions of 6.67±0.38 events from four-fermion processes and 0.14 −0.05 +0.19 from background processes.

We have studied the process e<sup loc="post">+</sup>e<sup loc="post">−</sup> → nγ (n ≥ 2) at an average center-of-mass energy of 133 GeV using the L3 detector at LEP. For an integrated luminosity of 4.95 pb<sup loc="post">−1</sup> we find one γγγγ(γ) final state with only hard photons. The rates of both γγγ and γγ events are consistent with QED expectations. The cross section of the reaction e<sup loc="post">+</sup>e<sup loc="post">−</sup> → γγ(γ) in the polar range 16° &lt; θγ < 164° is measured to be 22.6 ± 2.2 pb. Decays into photons of narrow scalar resonances with masses between 90 and 130 GeV are not observed. The observation of the event with four energetic photons is consistent with QED although the kinematic configuration of the photons is atypical.

We present a study of the structure of hadronic events recorded by the L3 detector at center-of-mass energies of 130 and 136 GeV. The data sample corresponds to an integrated luminosity of 5 pb −1 collected during the high energy run of 1995. The shapes of the event shape distributions and the energy dependence of their mean values are well reproduced by QCD models. From a comparison of the data with resummed O (α s 2 ) QCD calculations, we determine the strong coupling constant to be α s (133 GeV) = 0.107 ± 0.005(exp) ± 0.006(theor).