H. Ohsumi

Polarization and weak decays of Λ hypernuclei produced by the (π+, K+) reaction on 12C

Abstract Non-mesonic weak-decay protons (NM-p) and mesonic weak-decay pions (M-π) from Λ produced by the (π+, K+) reaction on 12C have been measured. NM-p from the 11 Λ B ( 5 2 + ) produced through the proton-unbound states in 12ΛC and NM-p and M-π associated with the quasi-bound region (Ex ≈ 20 MeV) in 12ΛC show finite asymmetries of A1 = − 0.20 to − 0.35 with respect to the reaction plane. These results indicate finite polarizations of the relevant Λ-hypernuclei and asymmetric NM weak decays.

Limits on neutrino-less double beta decay of 100Mo

Abstract Exclusive measurements of neutrino-less double beta decays (0νββ) of 100Mo were made by means of ELEGANT V. Most stringent lower limits on the half-lives for the ground-state transition were obtained for the 0νββ processes as T 1 2 0ν (m ν ) > 5.2 × 10 22 y , T 1 2 0ν (λ) > 3.9 × 10 22 y and T 1 2 0ν (η) > 5.1 × 10 22 y , for the mass term 〈mν〉, for the right-handed current terms of 〈λ〉 and 〈η〉, respectively, and as T 1 2 0νB > 5.4 × 10 21 y for the process (0νββB) followed by a Majoron (B). These limits lead to the upper limits of 〈mν〉

Limits on the annual modulation of WIMPs-nucleus scattering with large-volume NaI(Tl) scintillators

Abstract A search for cold dark matters has been carried out with the 662 kg NaI scintillator array of ELEGANT V at the Kamioka underground laboratory. The annual modulation of weakly interacting massive particles (WIMPs) energy spectra has been investigated. No significant modulations beyond statistical fluctuations were found. Stringent limits were obtained on masses and cross sections for both axial-vector coupled and vector coupled WIMPs.

Double beta decays and ELEGANT V and VI at Oto Cosmo Observatory

Abstract Exclusive measurements of neutrino-less double beta decays(0νββ) of 100 Mo were made by means of ELEGANT V at Kamioka Underground Laboratory. Oto Cosmo Observatory has been constructed for underground laboratory for ELEGANT V and VI for the study of 0νββ of 100 Mo and 48 Ca, search for dark matters and so on.

g Factors of the s Band in Er 164 and Yb 166

The g factors of the s-band 12/sup +/ levels in /sup 164/Er and /sup 166/Yb were studied by measuring ..gamma..-ray angular distributions and internal conversion coefficients with use of a new electron spectrometer for the interband 12/sub s//sup +/..-->..12/sub g//sup +/ transitions. The g factors were deduced for the first time to be g = 0.07 +- 0.03 for /sup 164/Er and -0.14 +- 0.04 for /sup 166/Yb. These small values indicate clearly the rotation alignment of the i/sub 13/2/ neutrons for the s band.

Continuum spectra of neutrons following the 92Zr(α,α') reaction

Abstract The mechanism of the 92 Zr( α , α ′n) reaction was studied by observing the neutron in coincidence with the inelastic alpha particle. Fast neutron groups from the direct knock-out and pre-equilibrium processes, and the slow neutron group from the equilibrium (evaporation) process were studied separately by α ′−n correlation measurements. Interactions between the incident alpha particle and the target nucleon are suggested to play an important role in the processes.

Search for exotic nuclear transition by using the large volume NaI detector of ELEGANTS V.

Abstract The authors studied elastic and inelastic scattering of dark matter with nuclei in huge NaI(Tl) scintillator. The light output response f was measured by fast neutron scattering. The result was f I = 0.05 ± 0.02 for I recoil and f Na = 0.4 ± 0.2 for Na recoil. The low noise (≅5keV) and low BG (≅8counts/day/keV/kg) was achieved by huge (36.5kg/module) NaI(Tl) scintillator. Strong limit for inelastic exitation of 127 I nuclei was studied and strong limit on the local halo density of spin coupled dark matter candidate was derived.

Double beta decays of 100MO and charge nonconserving transitions in 127I studied by means of elegants V

Abstract Double beta (ββ) decays of 100Mo and charge nonconserving (CNC) X-ray and γ-ray transitions in 127I were studied by means of ELEGANTS V. Afinite half-life of T 1 2 2ν = 1.15 −0.20 +0.30 × 10 19 yr(68%CL) for the two neutrino ββ decay and the lower limit of T 1 2 0ν > 7 × 10 21 yr(68%CL) for the neutrino-less ββ decay were obtained. This corresponds to the mass limit of mν 127 I + e K → 127 I ∗ + ν and 127 I + e K → 127 I + ν were obtained as τ > 5.8 × 1022yr and τ > 1.2 · 1023yr, respectively. Upper limits on the ratios of the CNC strengths to the charge conserving ones for the weak and electromagnetic processes were obtained as ϵW2

g factors of the s band in /sup 164/Er and /sup 166/Yb

The g factors of the s-band 12/sup +/ levels in /sup 164/Er and /sup 166/Yb were studied by measuring ..gamma..-ray angular distributions and internal conversion coefficients with use of a new electron spectrometer for the interband 12/sub s//sup +/..-->..12/sub g//sup +/ transitions. The g factors were deduced for the first time to be g = 0.07 +- 0.03 for /sup 164/Er and -0.14 +- 0.04 for /sup 166/Yb. These small values indicate clearly the rotation alignment of the i/sub 13/2/ neutrons for the s band.

Study of neutrino and dark matter by high sensitivity ββ, γ and X ray spectrometer ELEGANTS

Abstract Nuclear and particle rare decay and weak processes were studied by high sensitivity β-γ and X ray spectrometer ELEGANTS V. A finite value of half life for the two neutrino double beta decay of 100Mo ( T 1 2 2ν = 1.15 −0.20 +0.30 × 10 19 yr ) and the lower limit for neutrino less double beta decay ( T 1 2 0ν > 7 × 10 21 yr ) for 100Mo were obtained. Double beta decays of 116Cd has also been studied. The preliminaly half life for the two neutrino double beta decay ( T 1 2 2ν = 2.6 −0.6 +1.3 × 10 19 yr ) and the lower limit for neutrino less double beta decay ( T 1 2 0ν > 1.1 × 10 21 yr ) were obtained. The large volume NaI(Tl) scintillators in ELEGANTS V have been applied to search for cosmic cold dark matter candidates. The elastic scattering and inelastic scattering of dark matter and the nuclei in the NaI(Tl) scintillator were studied. The low back ground (⋍5/day/keV/kg) and low noise (⋍5keV) experiment was successfully done and stringent limit on the local density of dark matter candidates was given.