In a search for the decay ital Ksub ital Lsup 0r arrowital esup +ital eminus, no candidates have been observed. We determine the sensitivity from the detected number of ital CP-violating ital Ksub ...ital Lsup 0r arrowpisup +pisup minus decays and place a 90% confidence level upper limit on the branching ratio of ital B(ital Ksub ital Lsup 0r arrowital esup +ital eminus,vert barital Msub ital Kminusital Msub ital eital evert barlt6 MeV/ital csup 2)le4.1times10sup minus11. This result is a significant improvement over previous measurements, although still above the standard model prediction of 3times10sup minus12.
We report on a study of the relative rates of B meson decays into psi(2S) and J/psi mesons using 1.3 fb^-1 of pbar p collisions at sqrt(s) = 1.96 TeV recorded by the D0 detector operating at the ...Fermilab Tevatron Collider. We observe the channels B^0_s -> psi(2S)phi, B^0_s -> J/psi phi, B^+/- -> psi(2S) K^+/-, and B^+/- -> J/psi K^+/- and we measure the relative branching fractions for these channels to be B(B^0_s -> psi(2S)phi)/B(B^0_s -> J/psi phi) = 0.55 +/- 0.11 (stat) +/- 0.07 (syst) +/- 0.06 (B), B(B^+/- -> psi(2S) K^+/-)/B(B^+/- -> J/psi K^+/-) = 0.65 +/- 0.04 (stat) +/- 0.03 (syst) +/- 0.07 (B) where the final error corresponds to the uncertainty in the J/psi and psi(2S) branching ratio into two muons.
A search for the decay ital Ksub ital Lsup 0r arrowmusup plus minusital eminus plus with significantly increased experimental sensitivity has yielded no events. The 90% confidence level limit on the ...branching ratio is ital B(ital Ksub ital Lsup 0r arrowmusup plus minusital eminus plus)lt3.9times10sup minus11. When this data set is combined with earlier data the upper limit is 3.3times10sup minus11.
We describe the development and testing of a novel beam stop for use in a rare kaon decay experiment at the Brookhaven AGS. The beam stop is located inside a dipole spectrometer magnet in close ...proximity to straw drift chambers and intercepts a high-intensity neutral hadron beam. The design process, involving both Monte Carlo simulations and beam tests of alternative beam-stop shielding arrangements, had the goal of minimizing the leakage of particles from the beam stop and the resulting hit rates in detectors, while preserving maximum acceptance for events of interest. The beam tests consisted of measurements of rates in drift chambers, scintilation counter hodoscopes, a gas threshold Cherenkov counter, and a lead glass array. Measurements were also made with a set of specialized detectors which were sensitive to low-energy neutrons, photons, and charged particles. Comparisons are made between these measurements and a detailed Monte Carlo simulation.
We present a direct measurement of trilinear gauge boson couplings at gamma WW and ZWW vertices inWW and WZ events produced in p (p) over bar collisions at root s = 1:96 TeV. We consider events with ...one electron or muon, missing transverse energy, and at least two jets. The data were collected using the D0 detector and correspond to 1:1 fb(-1) of integrated luminosity. Considering two different relations between the couplings at the gamma WW and ZWW vertices, we measure these couplings at 68% C.L. to be kappa(gamma) = 1.07(-0.29)(+0.26) lambda = 0.00(-0.06)(+0.00), and g(1)(Z) = 1.04(-0.09)(+0.09) in a scenario respecting SU(2)(L) circle times U(1)(Y) gauge symmetry and kappa = 1.04(-0.11)(+0.11) and lambda = 0.00(-0.06)(+0.06) in an "equal couplings'' scenario.
We have measured the branching ratio for ital Ksub ital Lsup 0r arrowmusup +musup minus using our full data set obtained during running periods in 1988, 1989, and 1990. The total number of musup ...+musup minus candidates after a background subtraction is 707, which represents the largest sample to date of this rare decay mode. Our result is ital B(ital Ksub ital Lsup 0r arrowmusup +musup minus)=(6.86plus minus0.37)times10sup minus9, which is consistent with earlier results and very near the unitarity bound. The upper limit on ital B(ital Ksub ital Lsup 0r arrowmusup +musup minus) is used to set an upper limit on the real part of the amplitude ital scrA(ital Ksub ital Lsup 0r arrowmusup +musup minus); this is subsequently used to constrain the top quark mass ital msub ital t and the Wolfenstein parameter rho of the CKM matrix.
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