Initial measurements of Z-boson resonance parameters in e+e- annihilation.

We have measured the mass of the Z boson to be 91.110.23 GeV/c2, and its width to be 1.61-0.43+0.60 GeV. If we constrain the visible width to its standard-model value, we find the partial width to invisible decay modes to be 0.620.23 GeV, corresponding to 3.81.4 neutrino species. © 1989 The American Physical Society

Measurements of charged-particle inclusive distributions in hadronic decays of the Z boson.

We have measured inclusive distributions for charged particles in hadronic decays of the Z boson. The variables chosen for study were charged-particle multiplicity, scaled momentum, and momenta transverse to the sphericity axes. The distributions have been corrected for detector effects and are compared with data from ee- annihilation at lower energies and with the predictions of several QCD-based models. The data are in reasonable agreement with expectations. © 1990 The American Physical Society

Searches for new quarks and leptons produced in Z-boson decay.

We have searched for events with new-particle topologies in 390 hadronic Z decays with the Mark II detector at the SLAC Linear Collider. We place 95%-confidence-level lower limits of 40.7 GeV/c2 for the top-quark mass, 42.0 GeV/c2 for the mass of a fourth-generation charge -(1/3 quark, and 41.3 GeV/c2 for the mass of an unstable Dirac neutral lepton. © 1989 The American Physical Society

Direct search for pair production of heavy stable charged particles in Z decays.

A search for pair production of stable charged particles from Z decay has been performed with the Mark II detector at the SLAC Linear Collider. Particle masses are determined from momentum, ionization energy loss, and time-of-flight measurements. A limit excluding pair production of stable fourth-generation charged leptons and stable mirror fermions with masses between the muon mass and 36.3 GeV/c2 is set at the 95% confidence level. Pair production of stable supersymmetric scalar leptons with masses between the muon mass and 32.6 GeV/c2 is also excluded. © 1990 The American Physical Society

Measurements of Z-boson resonance parameters in e+e- annihilation.

We have measured the mass of the Z boson to be 91.14±0.12 GeV/c2, and its width to be 2.42-0.35+0.45 GeV. If we constrain the visible width to its standard-model value, we find the partial width to invisible decay modes to be 0.46±0.10 GeV, corresponding to 2.8±0.6 neutrino species, with a 95%-confidence-level upper limit of 3.9. © 1989 The American Physical Society

First measurements of hadronic decays of the Z boson.

We have observed hadronic final states produced in the decays of Z bosons. In order to study the parton structure of these events, we compare the distributions in sphericity, thurst, aplanarity, and number of jets to the predictions of several QCD-based models and to data from lower energies. The data and models agree within the present statistical precision. © 1989 The American Physical Society

Measurement of the bb-bar fraction in hadronic Z0 decays with precision vertex detectors.

We have measured the fraction of bb» events in hadronic Z0 decays, Rbb», using the vertex detector system of the Mark II detector at the SLAC Linear Collider. We tag bb» events by requiring the coincidence of three or more tracks with significant impact parameters. This tag is 50% efficient and results in a sample of 85% purity. We find Rbb»=0.251+0.049+0.030, in good agreement with other measurements and the standard model prediction. © 1991 The American Physical Society