J. R. Kane

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

Precision Measurements of the

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

K^-

.

and

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.}

\Sigma^-

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.

Masses

The masses of the K/sup -/ and ..sigma../sup -/ have been measured by use of exotic-atom x-ray transitions in Pb and W. The transitions used were free from contaminant nuclear ..gamma.. rays and strong-interaction effects. Two K/sup -/ transitions and three ..sigma../sup -/ transitions for each target satisfied these criteria. The results are M/sub K//sub =/ = 493.636 +- 0.011 MeV and M/sub ..sigma..//sub =/ = 1197.532 +- 0.057 MeV. The precision of these measurements is greater than that of any previous experiment. When combined with previous measurements they form a consistent set.

Measurement of kaonic X-rays from Al, Si, Ni and Cu

Abstract We have identified X-rays associated with stopped negative kaons in Al, Si, Ni and Cu. We report relative intensities, strong interaction energy shifts and strong interaction line broadenings. The measurements are found to be in good agreement with those predicted on the basis of a simple phenomenological potential except for the Ni (5 → 4) transition width.

Strong interaction effects in the 2p-1s transition in pionic neon

Abstract We present experimental results for the 2p-1s transition energy and the natural line-width of the 1s state in pionic neon. The line width ifΓ=14.5 ± 3.0 keV is in substantial agreement with semiphenomenological low-energy pion-nucleus interaction theories in the region A ≈ 20.