K. Suzuki

We have measured polarized Raman spectra in a 2.0 mu m GaN epitaxial layer of high quality, grown on a sapphire substrate. All symmetry-allowed optical phonons in GaN have been assigned as follows: A1(LO), 735 cm-1; A1(TO), 533 cm-1; E1(LO), 743 cm-1; E1(TO), 561 cm-1; E2, 144 and 569 cm-1. Using the Lyddane-Sachs-Teller relation, the static dielectric constants of GaN for the ordinary and extraordinary directions have been estimated as epsilon perpendicular to 0=9.28 and E/sub //0/=10.1. We have also observed quasi-LO phonons in GaN. A brief discussion on these will be given.

Super-Kamiokande (SK) can search for weakly interacting massive particles (WIMPs) by detecting neutrinos produced from WIMP annihilations occurring inside the Sun. In this analysis, we include neutrino events with interaction vertices in the detector in addition to upward-going muons produced in the surrounding rock. Compared to the previous result, which used the upward-going muons only, the signal acceptances for light (few-GeV/c^{2}-200-GeV/c^{2}) WIMPs are significantly increased. We fit 3903 days of SK data to search for the contribution of neutrinos from WIMP annihilation in the Sun. We found no significant excess over expected atmospheric-neutrino background and the result is interpreted in terms of upper limits on WIMP-nucleon elastic scattering cross sections under different assumptions about the annihilation channel. We set the current best limits on the spin-dependent WIMP-proton cross section for WIMP masses below 200 GeV/c^{2} (at 10 GeV/c^{2}, 1.49×10^{-39} cm^{2} for χχ→bb[over ¯] and 1.31×10^{-40} cm^{2} for χχ→τ^{+}τ^{-} annihilation channels), also ruling out some fraction of WIMP candidates with spin-independent coupling in the few-GeV/c^{2} mass range.

We have analyzed data of the DISTO experiment on the exclusive $pp\ensuremath{\rightarrow}p\ensuremath{\Lambda}{K}^{+}$ reaction at 2.85 GeV to search for a strongly bound compact ${K}^{\ensuremath{-}}pp(\ensuremath{\equiv}X)$ state to be formed in the $pp\ensuremath{\rightarrow}{K}^{+}+X$ reaction. The observed spectra of the ${K}^{+}$ missing mass and the $p\ensuremath{\Lambda}$ invariant-mass with high transverse momenta of $p$ and ${K}^{+}$ revealed a broad distinct peak of $26\mathrm{\text{\ensuremath{-}}}\ensuremath{\sigma}$ confidence with a mass ${M}_{X}=2267\ifmmode\pm\else\textpm\fi{}3(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}5(\mathrm{syst})\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ and a width ${\ensuremath{\Gamma}}_{X}=118\ifmmode\pm\else\textpm\fi{}8(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}10(\mathrm{syst})\text{ }\text{ }\mathrm{MeV}$. The enormously large cross section indicates formation of a compact ${K}^{\ensuremath{-}}pp$ with a large binding energy of ${B}_{K}=103\text{ }\text{ }\mathrm{MeV}$, which can be a possible gateway toward cold and dense kaonic nuclear matter.

Proton decay is not allowed in the Standard Model but is a signature prediction of Grand Unified Theories (GUTs). The Super-Kamiokande Collaboration reports results from its rigorous search for proton decay in two channels. The non-observation of proton decay sets new lower bounds on the proton lifetime and imposes stringent constraints on possible GUT and other Beyond the Standard Model scenarios.

Deeply bound $1s$ states of ${\ensuremath{\pi}}^{\ensuremath{-}}$ in $^{115,119,123}\mathrm{S}\mathrm{n}$ were preferentially observed using the $\mathrm{S}\mathrm{n}(d,^{3}\mathrm{H}\mathrm{e})$ pion-transfer reaction under the recoil-free condition. The $1s$ binding energies and widths were precisely determined and were used to deduce the isovector parameter of the $s$-wave pion-nucleus potential to be ${b}_{1}=\ensuremath{-}(0.115\ifmmode\pm\else\textpm\fi{}0.007){m}_{\ensuremath{\pi}}^{\ensuremath{-}1}$. The observed enhancement of $|{b}_{1}|$ over the free $\ensuremath{\pi}N$ value (${b}_{1}^{\mathrm{f}\mathrm{r}\mathrm{e}\mathrm{e}}/{b}_{1}=0.78\ifmmode\pm\else\textpm\fi{}0.05$) indicates a reduction of the chiral order parameter, ${f}_{\ensuremath{\pi}}^{*}(\ensuremath{\rho}{)}^{2}/{f}_{\ensuremath{\pi}}^{2}\ensuremath{\approx}0.64$, at the normal nuclear density, $\ensuremath{\rho}={\ensuremath{\rho}}_{0}$.