We have searched for supersymmetric particles in 528 Z decays with the Mark II detector at the SLAC Linear Collider. We place 95%-confidence-level lower mass limits on degenerate squarks, nondegenerate up-type squarks, nondegenerate down-type squarks, charginos, pair-produced unstable neutralinos, and neutralinos from associated production. © 1990 The American Physical Society.

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.

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.

We describe a search for the decay of the Z boson into pairs of doubly charged Higgs bosons with the Mark II detector operating at the SLAC Linear Collider. Each Higgs boson is assumed to decay into a same-sign leptonic pair. No event candidates are found in a sample of 528 Z decays. At the 95% confidence level, this result excludes the region of leptonic coupling gll3×10-7 and Higgs-boson mass 6.5MH 36.5 GeV/c2 for isotriplet (left-handed) Higgs bosons. Isosinglet (right-handed) Higgs bosons are excluded in the same gll interval and in the mass interval 7.3 MH 34.3 GeV/c2. © 1990 The American Physical Society.

We measured the differential jet-multiplicity distribution in e+e- annihilation with the Mark II detector. This distribution is compared with the second-order QCD prediction and s is determined to be 0.1230.0090.005 at ssSMZ (at the SLAC Linear Collider) and 0.1490.0020.007 at ss=29 GeV (at the SLAC storage ring PEP). The running of s between these two center-of-mass energies is consistent with the QCD prediction. © 1990 The American Physical Society.

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.

We search for events in the Mark II detector at SLAC Linear Collider with the topology of a Z boson decaying into a pair of long-lived massive particles. No events that are consistent with the search hypothesis are found. Interpreting the long-lived particle as a sequential Dirac neutrino 4 of the fourth generation, we exclude at the 95% confidence level a significant range of mixing-matrix elements of 4 to other-generation neutrinos for a 4 mass from 10 to 43 GeV/c2. © 1990 The American Physical Society.

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.

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.

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.