Showing papers by "Tsuyoshi Nakaya published in 1999"

Measurement of the decay K(L) ---> pi0 gamma gamma

Abstract: We report on a new measurement of the decay ${K}_{L}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}\ensuremath{\gamma}$ by the KTeV experiment at Fermilab. We determine the ${K}_{L}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}\ensuremath{\gamma}$ branching ratio to be $(1.68\ifmmode\pm\else\textpm\fi{}0.07\ifmmode\pm\else\textpm\fi{}0.08)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. Our data show the first evidence for a low-mass $\ensuremath{\gamma}\ensuremath{\gamma}$ signal as predicted by recent $O({p}^{6})$ chiral perturbation calculations which include vector meson exchange contributions. From our data, we extract a value for the effective vector coupling ${a}_{V}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}0.72\ifmmode\pm\else\textpm\fi{}0.05\ifmmode\pm\else\textpm\fi{}0.06$.

Light gluino search for decays containing pi+ pi- or pi0 from a neutral hadron beam at Fermilab

Abstract: We report on two null searches, one for the spontaneous appearance of $\pi^+\pi^-$ pairs, another for a single $\pi^0$, consistent with the decay of a long-lived neutral particle into hadrons and an unseen neutral particle. For the lowest level gluon-gluino bound state, known as the $R^0$, we exclude the decays $R^0\to \pi^+\pi^-\tilde{\gamma}$ and $R^0\to \pi^0\tilde{\gamma}$ for the masses of $R^0$ and $\tilde{\gamma}$ in the theoretically allowed range. In the most interesting $R^0$ mass range, $\leq 3 GeV/c^2$, we exclude $R^0$ lifetimes from $3\times 10^{-10}$ seconds to as high as $10^{-3}$ seconds, assuming perturbative QCD production for the $R^0$.

Observation of the DecayΞ0→Σ+e−ν¯e

Abstract: We present the first observation of ${\ensuremath{\Xi}}^{0}$ beta decay, using the KTeV beam line and detector at Fermilab. We have identified 176 beta decay events after subtracting a 7 event background. Normalization to 41 024 simultaneously collected ${\ensuremath{\Xi}}^{0}\ensuremath{\rightarrow}{\ensuremath{\Lambda}}^{0}{\ensuremath{\pi}}^{0}$ decays yields a branching ratio of $\ensuremath{\Gamma}({\ensuremath{\Xi}}^{0}\ensuremath{\rightarrow}{\ensuremath{\Sigma}}^{+}{e}^{\ensuremath{-}}{\overline{\ensuremath{ u}}}_{e})/{\ensuremath{\Gamma}}_{\mathrm{total}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(2.71\ifmmode\pm\else\textpm\fi{}{0.22}_{\mathrm{statistical}}\ifmmode\pm\else\textpm\fi{}{0.31}_{\mathrm{systematic}})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. The flavor symmetric quark model calculation agrees with this result.