We have tested QED to fourth order in the coupling constant in the large-Q2 region by studying four-lepton final states in e+e- interactions with the Mark II detector at the SLAC storage ring PEP (s=29 GeV). All four final-state particles were detected at large angles with respect to the beam axis. For an integrated luminosity of 205 pb-1, we observed ten e+e-e+e-, ten e+e-+-, and one events with opposite-charge pair masses greater than 1 GeV/c2. These events show good agreement with the complete 4 QED calculation. © 1990 The American Physical Society.

The τ lifetime was measured with the Mark II vertex detector at the storage ring PEP. ττ=(3.20±0.41±0.35)×10-13 sec was found, which agrees well with e-μ-τ university. © 1983 The American Physical Society.

We present results on c+ production in 29-GeV e+e- annihilation. The c+ are observed via their semileptonic decays to e+X and +X. With radiative corrections, we find (e+e-c+X)Bc+eX)= 1.5±0.6±0.5 pb or 0.0038±0.0015±0.0012 c+e+X decay per hadronic event, and (e+e-c+X)B(c+X)= 1.4±1.4±0.4 pb or 0.0035±0.0035±0. 0011 c++X decay per hadronic event. These results can be used to place constraints on the predictions of various production models. © 1989 The American Physical Society.

We present a high statistics measurement of the branching ratio for the decay τ-→π-μτ using data obtained with the Mark II detector at the SLAC e+e- storage ring SPEAR. We have used events from the center-of-mass energy region 3.52 to 6.7 GeV to determine that B(τ-→π-μτ)=0.117±0.004±0.018. From electron-muon events in the same data sample, we have determined that B(τ-→π-μτ) B(τ-→e--μeμτ)=0.66±0.03±0.11. We present measurements of the mass and spin of the τ and the mass of the τ neutrino based, for the first time, on a hadronic decay mode of the τ. © 1982.

The process e+e-e+e-(), where one electron scatters at a small angle, is studied with data from the Mark II detector at the SLAC storage ring PEP. The data are in excellent agreement with a Monte Carlo calculation and include a large contribution from order 4. The ratio of measured to calculated cross sections is R=0.9930.0170.015, where the first error is statistical and the second systematic. This is a sensitive test of the calculation of the dominant background for neutrino-counting experiments. © 1989 The American Physical Society.

Energy correlations have been measured with the MARK II detector at the PEP storage ring (Stanford Linear Accelerator Center) at c.m. energy of 29 GeV and are compared to first-order QCD predictions. Fragmentation processes are significant and limit the precision with which the first-order strong-coupling constant can be determined. © 1982 The American Physical Society.

We have searched for a heavy charged lepton with an associated neutrino of nearly the same mass in e+e- annihilation data taken with the Mark II detector at a center-of-mass energy of 29 GeV. In order to suppress contamination from conventional two-photon reactions, this analysis uses a novel, radiative-tagging technique. Requiring the presence of an isolated, energetic photon allows a search for lepton doublets with mass splittings smaller than that previously accessible to experiment. No evidence for such a new lepton doublet has been found, enabling limits to be placed on allowed mass combinations. Mass splittings as low as 250-400 MeV/c2 are excluded for charged-lepton masses between 500 MeV/c2 and 10 GeV/c2. © 1990 The American Physical Society.