J. McDonough

Search for the decay micro+-->e+ gamma.

This Letter reports a new experimental search for the family-number-nonconserving decay ..mu../sup +/ ..-->.. e/sup +/..gamma... There is no evidence for the presence of this decay mode. The upper limit for the branching ratio is GAMMA(..mu.. ..-->.. e..gamma..)/GAMMA(..mu.. ..-->.. enu anti nu) < 4.9 x 10/sup -11/ (90% C.L.). 13 refs., 3 figs.

New limit on muon and electron lepton number violation from K0(L) ---> mu+- e-+ decay

The most sensitive experiment to date to search for the muon and electron lepton number violating decay

Search for the weak decay of an H dibaryon.

K^0_L \to \mu^\pm e^\mp

First observation of the rare decay mode K0(L) ---> e+ e-

has detected no events consistent with this process. Based on this result, the 90% confidence level upper limit on the branching fraction is

A compact beam stop for a rare kaon decay experiment

B(K^0_L \to \mu^\pm e^\mp) < 4.7\times10^{-12}

A straw drift chamber spectrometer for studies of rare kaon decays

.

New Limit on Muon and Electron Lepton Number Violation from K{sup 0}{sub L} {r_arrow} {mu}{sup {plus_minus} }e{sup {minus_plus}} Decay

We have searched for a neutral {ital H} dibaryon decaying via {ital H}{r_arrow}{Lambda}{ital n} and {ital H}{r_arrow}{Sigma}{sup 0}{ital n}. Our search has yielded two candidate events from which we set an upper limit on the {ital H} production cross section. Normalizing to the inclusive {Lambda} production cross section, we find ({ital d}{sigma}{sub {ital H}}/{ital d}{Omega})/({ital d}{sigma}{sub {Lambda}}/{ital d}{Omega}){lt}6.3{times}10{sup {minus}6} at 90{percent} C.L., for an {ital H} of mass {approx_equal}2.15 GeV/{ital c}{sup 2}. {copyright} {ital 1996 The American Physical Society.}

Search for the Decayμ+→e+γ

In an experiment designed to search for and study very rare two-body decay modes of the K-long, we have observed four examples of the decay K-long -> e+ e-, where the expected background is 0.17+-0.10 events. This observation translates into a branching fraction of 8.7^{+5.7}_{-4.1} X 10^{-12}, consistent with recent theoretical predictions. This result represents by far the smallest branching fraction yet measured in particle physics.

Search for the Decay

Abstract We describe the development and testing of a novel beam stop for use in a rare kaon decay experiment at the Brookhaven Alternating Gradient Synchrotron. 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, scintillation 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.

\mu^+ \to e^+ \gamma

We describe the design, construction, readout, tests, and performance of planar drift chambers, based on 5-mm-diameter copperized Mylar and Kapton straws, used in an experimental search for rare kaon decays. The experiment took place in the high-intensity neutral beam at the Alternating Gradient Synchrotron of Brookhaven National Laboratory, using a neutral beam stop, two analyzing dipoles, and redundant particle identification to remove backgrounds.