Search

We have measured the branching ratio of the three-body process in the nonmesonic weak decay of {sub {Lambda}{sup 12}}C to be 0.29+-0.13. This result was obtained by reproducing the nucleon and the nucleon pair yields introducing a measured final state interaction. At the same time, we have determined the absolute decay widths, GAMMA{sub n} and GAMMA{sub p}, along with GAMMA{sub 2N}, whose relative ratio has been a long-standing puzzle. Including the three-body process, we have successfully reproduced the nucleon energy distribution, the coincidence two-nucleon angular correlation, and the momentum sum distribution simultaneously.

We performed a coincidence measurement of two nucleons emitted from the nonmesonic weak decay (NMWD) of ^{5}_{\Lambda}He formed via the ^{6}Li(\pi^+,K^+) reaction. The energies of two nucleons and the pair number distributions in the opening angle between them were measured. In both np and nn pairs, we observed a clean back-to-back correlation coming from the two-body decay of \Lambda p --> n p and \Lambda n --> n n, respectively. The ratio of the nucleon pair numbers was N_{nn}/N_{np}=0.45 \pm 0.11(stat)\pm 0.03(syst) in the kinematic region of cos(theta_{NN}) np)/\Gamma(\Lambda n --> nn). The ratio is consistent with recent theoretical calculations based on the heavy meson/direct quark exchange picture.

In order to produce a neutron-rich $\ensuremath{\Lambda}$ hypernucleus for the first time, we carried out an experiment by utilizing the $({\ensuremath{\pi}}^{\ensuremath{-}},{K}^{+})$ double charge-exchange reaction on a $^{10}\mathrm{B}$ target. We observed the production of a $_{\ensuremath{\Lambda}}^{10}\mathrm{L}\mathrm{i}$ hypernucleus. The cross section for the $\ensuremath{\Lambda}$ bound region was found to be $11.3\ifmmode\pm\else\textpm\fi{}1.9\text{ }\text{ }\mathrm{n}\mathrm{b}/\mathrm{s}\mathrm{r}$ with the $1.2\text{ }\text{ }\mathrm{G}\mathrm{e}\mathrm{V}/c$ incident momentum, which is compared with the $_{\ensuremath{\Lambda}}^{10}\mathrm{B}$ hypernucleus production cross section, $7.8\ifmmode\pm\else\textpm\fi{}0.3\text{ }\text{ }\ensuremath{\mu}\mathrm{b}/\mathrm{s}\mathrm{r}$, in the $({\ensuremath{\pi}}^{+},{K}^{+})$ reaction with a $1.05\text{ }\text{ }\mathrm{G}\mathrm{e}\mathrm{V}/c$ incident momentum beam.

A new operational scenario of advanced tokamak formation was demonstrated in the JT-60U tokamak. This was accomplished by electron cyclotron and lower hybrid waves, neutral beam injection, and the loop voltage supplied by the vertical field and shaping coils. The Ohmic heating (OH) solenoid was not used but a small inboard coil (part of the shaping coil), providing less than $20%$ of total poloidal flux, was used. The plasma thus obtained had both internal and edge transport barriers, with an energy confinement time of 1.6 times H-mode scaling, a poloidal beta of 3.6, and a normalized beta of 1.6, and a large bootstrap current fraction ($g90%$). This result opens up a possibility to reduce, and eventually eliminate, the OH solenoid from a tokamak reactor, which will greatly improve its economic competitiveness.

We have studied the (π - , K + ) reaction on a silicon target to investigate the sigma-nucleus potential. The inclusive spectrum was measured at a beam momentum of 1.2 GeV/c with an energy resolution of 3.3 MeV (FWHM) by employing the superconducting kaon spectrometer system. The spectrum was compared with theoretical calculations within the framework of the distorted-wave impulse approximation, which demonstrates that a strongly repulsive sigma-nucleus potential with a nonzero size of the imaginary part reproduces the observed spectrum.

A double-hyperfragment event has been found in a hybrid-emulsion experiment. It is identified uniquely as the sequential decay of ${}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}^{6}\mathrm{He}$ emitted from a ${\ensuremath{\Xi}}^{\ensuremath{-}}$ hyperon nuclear capture at rest. The mass of ${}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}^{6}\mathrm{He}$ and the $\ensuremath{\Lambda}\ensuremath{-}\ensuremath{\Lambda}$ interaction energy $\ensuremath{\Delta}{B}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}$ have been measured for the first time devoid of the ambiguities due to the possibilities of excited states. The value of $\ensuremath{\Delta}{B}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}$ is $1.01\ifmmode\pm\else\textpm\fi{}{0.20}_{\ensuremath{-}0.11}^{+0.18}\phantom{\rule{0ex}{0ex}}\mathrm{MeV}$. This demonstrates that the $\ensuremath{\Lambda}\ensuremath{-}\ensuremath{\Lambda}$ interaction is weakly attractive.

An experiment demonstrating the production of double-Lambda hypernuclei in (K(-),K(+)) reactions on (9)Be was carried out at the D6 line in the BNL alternating-gradient synchrotron. The technique was the observation of pions produced in sequential mesonic weak decay, each pion associated with one unit of strangeness change. The results indicate the production of a significant number of the double hypernucleus (4)(double Lambda)H and the twin hypernuclei (4)(Lambda)H and (3)(Lambda)H. The relevant decay chains are discussed and a simple model of the production mechanism is presented. An implication of this experiment is that the existence of an S = -2 dibaryon more than a few MeV below the double Lambda mass is unlikely.

Gamma decay of the low-energy octupole resonance in /sup 90/Zr was studied by inelastic ..cap alpha.. scattering at 99.3 MeV. Correlation functions measured for the ground-state transition support a spin-3 assignment for the low-energy octupole resonance. Observed branching ratios to the ground and the low-lying states around E/sub x/approx.2.2 MeV are respectively (7.9 +- 1.0)% and (32 +- 10)%, which are significantly larger than those predicted by the statistical-decay model.

A correlation experiment between inelastically scattered /sup 3/He particles at 1.2/sup 0/ and decay ..cap alpha.. particles was performed in the giant-resonance region of /sup 40/Ca at an incident energy of 120 MeV. A new 0/sup +/ state with 6% energy-weighted sum-rule strength was observed at E/sub x/ = 14.2 MeV. Two broad resonances (quadrupole and possibly octupole) were observed at E/sub x/ approx. 18 MeV. No resonant structure was observed at E/sub x/ > 20 MeV.