Search

We report results of a search for the lepton-family number violating decay K+-->pi(+)m(+)e(-) from data collected by experiment E865 in 1996 at the Alternating Gradient Synchroton of Brookhaven National Laboratory. We place an upper limit on the branching ratio at 3.9x10(-11) ( 90% C.L.). Together with results based on data collected in 1995 and an earlier experiment, E777, this result establishes a combined 90% confidence level upper limit on the branching ratio at 2.8x10(-11). We also report a new upper limit on the branching ratio for pi(0)-->m(+)e(-) of 3.8x10(-10) ( 90% C. L.).

More than 400 $K^{+}\to\pi^{+}\mu^+\mu^-$ events were observed in a rare $K^+$ decay experiment at the AGS. Normalized to the $K^{+}\to\pi^{+}\pi^+\pi^-$ decay, the branching ratio is determined to be $(9.22 \pm 0.60 (stat) \pm 0.49 (syst))\times 10^{-8}$. This branching ratio and the $\mu\mu$ mass spectrum is in very good agreement with the measurement of the $K^{+}\to\pi^{+}e^+e^-$ decay, but deviates significantly from the previous measurement.

A low-background sample of 10 300 events has been collected for the decay mode K{sup +}{yields}{pi}{sup +}e{sup +}e{sup -} by experiment E865 at the Brookhaven Alternating Gradient Synchrotron. The branching ratio is measured to be [2.94{+-}0.05(stat){+-}0 .13(syst){+-}0.05(model )]x10{sup -7} , the vector nature of this decay is firmly established, and the decay form factor f(z)=f{sub 0}(1+{delta}z) (z=M{sup 2}{sub ee}/m{sup 2}{sub K} ) is determined to have {delta}=2.14{+-}0.13{+-}0.15 . The experiment is described and results discussed in the context of chiral perturbation theory. (c) 1999 The American Physical Society.

Experiment 865 at the Brookhaven AGS has observed the decay K{sup +}{yields}e{sup +}{nu}{sub e}{mu}{sup +}{mu}{sup -}. The branching ratio extracted is (1.72{+-}0.37(stat){+-}0.17(syst){+-}0.19(model))x10{sup -8} where the third term in the error results from the use of a model to extrapolate into a kinematic region dominated by background.

Based on results of a search for the lepton-family-number-violating decay K{sup +}{yields}{pi}{sup +}{mu}{sup +}e{sup -} with data collected by experiment E865 at the Alternating Gradient Synchrotron of Brookhaven National Laboratory, we place an upper limit on the branching ratio at 2.1x10{sup -11} (90% C.L.). Combining the results with earlier E865 data and those of a previous experiment, E777, an upper limit on the branching ratio of 1.3x10{sup -11} (90% C.L.) is obtained.

E865 at the Brookhaven National Laboratory AGS collected about 70 000 K(+)(e3) events to measure the K(+)(e3) branching ratio relative to the observed K+-->pi(+)pi(0), K+-->pi(0)micro(+)nu, and K+-->pi(+)pi(0)pi(0) decays. The pi(0) in all the decays was detected using the e(+)e(-) pair from pi(0)-->e(+)e(-)gamma decay and no photons were required. Using the 2002 Particle Data Group branching ratios for the normalization decays, we obtain BR(K(+)(e3(gamma)))=(5.13+/-0.02(stat)+/-0.09(syst)+/-0.04(norm))%, where K(+)(e3(gamma)) includes the effect of virtual and real photons. This result is approximately 2.3sigma higher than the current Particle Data Group value. Implications for the V(us) element of the CKM matrix, and the matrix's unitarity are discussed.

We report experimental details and results of a new measurement of the decay ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{e}^{+}{\ensuremath{\nu}}_{e}{(K}_{e4}).$ A sample of more than $400,000{K}_{e4}$ events with low background has been collected by Experiment 865 at the Brookhaven Alternate Gradient Synchrotron. From these data, the branching ratio $(4.11\ifmmode\pm\else\textpm\fi{}0.01\ifmmode\pm\else\textpm\fi{}0.11)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ and the $\ensuremath{\pi}\ensuremath{\pi}$ invariant mass dependence of the form factors $F,G,$ and H of the weak hadronic current as well as the phase shift difference ${\ensuremath{\delta}}_{0}^{0}\ensuremath{-}{\ensuremath{\delta}}_{1}^{1}$ for $\ensuremath{\pi}\ensuremath{\pi}$ scattering were extracted. Using constraints based on analyticity and chiral symmetry, a new value with considerably improved accuracy for the s-wave $\ensuremath{\pi}\ensuremath{\pi}$ scattering length ${a}_{0}^{0}$ has been obtained also: ${a}_{0}^{0}=0.216\ifmmode\pm\else\textpm\fi{}0.013(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.002(\mathrm{syst})\ifmmode\pm\else\textpm\fi{}0.002(\mathrm{theor}).$

A sample of $4\ifmmode\times\else\texttimes\fi{}{10}^{5}$ events from the decay ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{e}^{+}{\ensuremath{\nu}}_{e}\phantom{\rule{0ex}{0ex}}({K}_{e4})$ has been collected in experiment E865 at the Brookhaven Alternating Gradient Synchrotron. The analysis of these data yields new measurements of the ${K}_{e4}$ branching ratio $[(4.11\ifmmode\pm\else\textpm\fi{}0.01\ifmmode\pm\else\textpm\fi{}0.11)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}]$, the $s$-wave $\ensuremath{\pi}\ensuremath{\pi}$ scattering length $[{a}_{0}^{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.216\ifmmode\pm\else\textpm\fi{}0.013(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.004(\mathrm{syst})\ifmmode\pm\else\textpm\fi{}0.005(\mathrm{theor})]$, and the form factors $F$, $G$, and $H$ of the hadronic current and their dependence on the invariant $\ensuremath{\pi}\ensuremath{\pi}$ mass.