Experiments at MIT-Bates(I. Nuclear Physics)

We have been collaborating with a group of University of Massachusetts since 1988 for experiments at MIT-Bates. Bates Experiment #89-09 (Measurement of the Elastic Magnetic Form Factor and the Threshold Breakup of ^3He at High Momentum Transfer) was accepted in 1989 and performed in 1997. Data analysis of the experiment was completed using one and a half years. A new proposal, Bates-Experiment #97-03 (Virtual Compton Scattering on the Proton Below Pion Threshold) has been scheduled in the early summer of 2000

Measurement of the 6Li(e,e'p) reaction cross sections at low momentum transfer

The triple differential cross sections for the 6Li(e,e'p) reaction have been measured in the excitation energy region from 27 to 46 MeV in a search for evidence of the giant dipole resonance (GDR) in 6Li. The cross sections have no distinct structures in this energy region, and decrease smoothly with the energy transfer. Angular distributions are different from those expected with the GDR. Protons are emitted strongly in the momentum-transfer direction. The data are well reproduced by a DWIA calculation assuming a direct proton knockout process.Comment: 19 pages, 7 figures, revised text, to be published in Nucl. Phys.

Study of (e, e\u27 α) Reaction on ^9Be(I. Nuclear Physics)

The (e, e\u27 a) cross section has been measured at energy transfers from 10.0 to 28.4 MeV and a momentum transfer of 99 MeV/c, using a 197 MeV continuous electron beam. The cross section rapidly increases with decreasing energy at angles smaller than 25°, while it appears flat at larger angles. The forward-peaked angular distribution was observed below 18 MeV, and the forward peak shrinks at higher energies. An amount of αparticles from decay of ^5He is estimated

Photo-production of neutral kaons on 12C in the threshold region

Kaon photo-production process on $^{12}$C has been studied by measuring neutral kaons in a photon energy range of 0.8$-$1.1 GeV. Neutral kaons were identified by the invariant mass constructed from two charged pions emitted in the $K^{0}_{S}\to\pi^{+}\pi^{-}$ decay channel. The differential cross sections as well as the integrated ones in the threshold photon energy region were obtained. The obtained momentum spectra were compared with a Spectator model calculation using elementary amplitudes of kaon photo-production given by recent isobar models. Present result provides, for the first time, the information on $n(\gamma,K^{0})\Lambda$ reaction which is expected to play an important role to construct models for strangeness production by the electromagnetic interaction. Experimental results show that cross section of $^{12}{\rm C}(\gamma,K^0)$ is of the same order to that of $^{12}{\rm C}(\gamma,K^+)$ and suggest that slightly backward $K^0$ angular distribution is favored in the $\gamma n\to K^0\Lambda$ process.Comment: 6 pages, 8 figure

Experimental Study of Photonuclear Reactions of ^4He below Pion Threshold(I. Nuclear Physics)

An experimental method for the precise measurement of the photonuclear reactions of ^4He below the pion threshold has been tested. We used a tagged photon beam and a time projection chamber containing helium gas, which served as an active target. It was proved that the chamber could successfully detect the tracks of the charged particles from the photonuclear reactions in a high radiation level due to the irradiation of a high-intensity photon beam. It was found that the background was mainly due to the noise of the chamber, and could be suppressed by taking coincidence of the signals from the chamber and the tagging counter

Measurement of the double-\beta decay half-life of ^{136}Xe with the KamLAND-Zen experiment

We present results from the KamLAND-Zen double-beta decay experiment based on an exposure of 77.6 days with 129 kg of $^{136}$Xe. The measured two-neutrino double-beta decay half-life of $^{136}$Xe is $T_{1/2}^{2\nu} = 2.38 \pm 0.02(stat) \pm 0.14(syst) \times 10^{21}$ yr, consistent with a recent measurement by EXO-200. We also obtain a lower limit for the neutrinoless double-beta decay half-life, $T_{1/2}^{0\nu} > 5.7 \times 10^{24}$ yr at 90% confidence level (C.L.), which corresponds to almost a five-fold improvement over previous limits.Comment: 6 pages, 4 figures. Version as published in PR

Search for Two Nucleon States by the ^<12>C (γ, pn) ^<10>B Reaction(I. Nuclear Physics)

We performed the ^C(γ, pn) experiment using tagged photons in an energy range from 30 to 120 MeV. Protons and neutrons were detected by a range telescope and NE213 liquid scintillators, respectively. Missing energy spectra of the ^C(γ, pn) reaction were deduced to search for the two nucleon excited states. In this report, we show the experimental setup for the ^C(γ, pn) reaction using the tagged photon beams. The preliminary results are shown and discussed. The data analysis is in progress