The design and operation of precision drift chambers with multisampling as well as the concepts and methods for reaching an extraordinary degree of precision in mechanics and calibration are described. Specific instruments were developed for this purpose. The concept of reproducible positioning and the implementation to 30 μm accuracy, showing stability over three years, is given. Calibration and analysis with UV-laser and cosmic test measurements are outlined with the critical results. The experience of calibration and reliability of the large system in an actual L3 running experiment is analyzed. The resolution under “battle conditions” at LEP resulted in Δpp = (2.50±0.04)% at 45.6 GeV and will be presented in detail. The concept is well suited for future TeV energies.

The L3 detector is designed to measure the muon momentum with a 2% resolution at p = 45 GeV/c. We discuss here the systems we developed to reach the required accuracy and control the mechanical alignment at running time. We also report on the test done on the muon spectrometer with UV lasers and cosmic rays.

We have measured the partial widths of the Z0 into lepton pairs, and the forward-backward charge asymmetry for the process e+e−→μ+μ− using the L3 detector at LEP. We obtain an average Γℓℓ of 83.0±2.1±1.1 MeV.From this result and the asymmetry measurement, we extract the values of the vector and axial vector couplings of the Z0 to leptons: grmv=−0.066−0.027+0.046 and grmA= −0.495−0.007+0.007.

Measurements of cosmic rays in the L3 multisampling chambers are presented. The study of tracks with polar angles from 30° < θ < 130° w.r.t. the wires show increasing pulse height like 1/sin θ. Using inclined tracks, we find a ±1.5 cm region of reduced accuracy near the glass supports of the 5.4 m long wires.

We have measured both the rates and the forward-backward asymmetry of ℓ+ℓ− from Z0→ℓ+ℓ− (where ℓ=μ, τ) with the L3 detector. We obtained Γℓℓ=88±4±3 MeV and the vector neutral current coupling constant, gv=0.00±0.07 and the axial vector neutral current coupling constant, gA=−0.515±0.015.

The L3 experiment is one of the six large detectors designed for the new generation of electron-positron accelerators. It is the only detector that concentrates its efforts on limited goals of measuring electrons, muons and photons. By not attempting to identify hadrons, L3 has been able to provide an order of magnitude better resolution for electrons, muons and photons. Vertices and hadron jets are also studied. The construction of L3 has involved much state of the art technology in new principles of vertex detection and in new crystals for large scale electromagnetic shower detection and ultraprecise muon detection. This paper presents a summary of the construction of L3.

We have measured the properties of Z0 → bb decays using a sample of 944 inclusive muon events, corresponding to 18 000 hadron events obtained with the L3 detector at LEP. We measured the partial decay width of the Z0 into bb, Γbb=353±48 MeV, and we determined the vector coupling of the Z0 to the b quark; grmv2(b)=0.095±0.047. We measured the forward-backward charge asymmetry in e+e− → bb events at √s≈Mv, and obtained Abb=13.3±9.9%.

We have made a precise measurement of the cross section for e+e−→Z0→hadrons with the L3 detector at LEP, covering the s 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, ΓZ0=2.539±0.054 GeV, and σh(MZ0)=29.5±0.7 nb. We also used the fit to the Z0 peak cross section and the width todetermine Γinvisible=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 4σ confidence level.

We report the results of first physics runs of the L3 detector at LEP. Based on 2538 hadron events, we determined the mass mz0 and the width Γz0 of the intermediate vector boson Z0 to be mz0=91.132±0.057 GeV (not including the 46 MeV LEP machine energy uncertainty) and Γz0=2.588±0.137 GeV. We also determined Γinvisible=0.567±0.080 GeV, corresponding to 3.42±0.48 number of neutrino flavors. We also measured the muon pair cross section and determined the branching ratio Γμμ=Γh=0.056±0.006. The partial width of Z0→e+e− is Γee=88±9±7 MeV.

The L3 muon spectrometer is presented. Characteristics, useful for experiments at future accelerators, are highlighted. Particular emphasis is given to the systems envisaged to keep the error on the relative alignment of detectors below 30 μm and so reach a momentum resolution Δpp = 2% at p = 45 GeV/c.

We have searched for scalar muons μ, scalar electrons ẽ, and winos W̃ from the reactions e+e− →ẽ+ẽ−, μ+μ−, W̃+W̃− at √s ∼ 91 GeV with an integrated luminosity of 157 nb −1. We have searched for μ+μ−, e+e−, or e−μ final states with missing transverse momentum PT > 6 GeV. These final states are signatures for the production of ẽ, μ, and W̃. We found no events. Our results are Mμ > 41 GeV, Mẽ > 41 GeV, and MW̃ > 44 GeV at the 95% confidence level.

Methods allowing the precise determination of momenta in the TeV region are demonstrated. Their application in future collider detectors will enable, by magnetic analysis, 1–2% mass resolution for 1 TeV dimuons.

Data accumulated with a high-precision vertex drift chamber operating in the MAC detector at the SLAC storage ring PEP are used for a precise measurement of the lifetime of the \ensuremath{\tau} lepton. We measure decay lengths of a sample of reconstructed three-prong decay vertices, and impact parameters of a separate sample of decay tracks. Combining these results, we find that ${\ensuremath{\tau}}_{\ensuremath{\tau}}$=0.309\ifmmode\pm\else\textpm\fi{}0.019 ps, in agreement with the prediction from the measured leptonic branching ratio and \ensuremath{\tau}-\ensuremath{\mu} universality.

A prototype of the L3 muon chamber module, designed for measuring muon track positions, was built and tested. Measured simulated tracks made by an UV laser beam used for the internal alignment of the chambers in the module appeared to display a systematic positional error. The module measures the slope of laser tracks with high precision. The induced charge mechanism of proportional chambers creates an error in the slope of the same track if measured using a single wire plane. A simulation of the wire signals resulted in a good description of the error; also the calculated decrease in the signal size for tracks parallel to the wire plane tallied with the measurements.