Using isolated leptons reconstructed in the Mark II detector to tag bb events, we measure the fraction of bb events in hadronic Z0 decays to be 0.23-0.09+0.11, in good agreement with the standard-model prediction of 0.22. We find (Zbb)=0.43-0.17+0.21 GeV. © 1990 The American Physical Society.

A precise measurement of the ratio R of the total cross section e+e-hadrons to the pointlike cross section e+e-+- at a center-of-mass energy of 29.0 GeV is presented. The data were taken with the upgraded Mark II detector at the SLAC storage ring PEP. The result is R=3.920.050.09. The luminosity has been determined with three independent luminosity monitors measuring Bhabha scattering at different angular intervals. Recent calculations of higher-order QED radiative corrections are used to estimate the systematic error due to missing higher-order radiative corrections in the Monte Carlo event generators. © 1991 The American Physical Society.

We use data from the Mark II experiment at PEP to search for the process B→h0X for mh0 between 50 and 210 MeV/c2. No evidence for the Higgs boson is seen in this mass range. The limit obtained rules out the standard Higgs boson for masses between 70 and 210 MeV/c2 and significantly constrains extensions of the Higgs sector. © 1989.

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.

Using an impact-parameter tag to select an enriched sample of Z0bb» events, we have measured the difference between the average charged multiplicity of bb» and all hadronic Z0 decays to be 2.11.8(stat) 0.6(syst) tracks per event. The resulting total (nonleading) charged multiplicity for Z0 bb» events is 23.1(12.0)1.8 0.6 tracks. A comparison of this nonleading multiplicity to hadronic multiplicity data in the range of 10 to 60 GeV supports the hypothesis of flavor-independent hadronic fragmentation, and yields a measurement of the average energy fraction of bottom hadrons in Z0 decays of xEb=0.620.100.04. © 1992 The American Physical Society.

Data taken by the Mark II detector at the SLAC e+e- storage ring PEP was used to search for exclusive decays of D and B mesons into two charged leptons plus a charged pion or kaon. All possible charge and lepton combinations consistent with charge conservation were considered and no evidence for any signals was found. We obtain upper limits for the various branching ratios ranging from 2.5×10-3 to 9.2×10-3, at a 90% confidence level. Some of these limits can be used to constrain leptoquark masses in various models. © 1990 The American Physical Society.

Data taken by the Mark II detector at the PEP storage ring was used to measure the rate of dilepton production in multihadronic events produced by e+e- annihilation at √s=29 GeV. We determine the probability that a hadron initially containing a b (b̄) quark decays to a positive (negative) lepton to be 0.17-0.08+0.15, with 90% confidence level limits of 0.06 and 0.38. © 1990.

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.

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 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.