T. Kishimoto

γ-ray spectroscopy in Λ hypernuclei

Abstract The present status of hypernuclear γ -ray spectroscopy with Hyperball is summarized. We observed two γ transitions of 16 Λ O( 1 − → 1 − , 0 − ) and obtained the strength of the ΛN tensor force. In 10 B( K − , π − γ ) data, we did not observe the spin-flip M1 transition of 10 Λ B( 2 − → 1 − ), but γ rays from hyperfragments such as 7 Λ Li( 7 / 2 + → 5 / 2 + ) and 9 Λ Be( 3 / 2 + → 1 / 2 + ) were observed. In 11 B( π + , K + γ ) data, we observed six γ transitions of 11 Λ B. We also attempted an inclusive γ -ray measurement with a stopped K − beam.

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〉

Spin polarization of λ hypernuclei produced by compound process of (π+, K+xnypγ) reactions

Abstract λ hypernuclear states with spin polarization are shown to be populated through nucleon and γ decays of compound λ hypernuclei produced by resonant ( π + , K + x n y p γ ) reactions. The low-lying Λ-hypernuclear states have the λ hyperon in the lowest 1 s 1 2 orbit. The intrinsic spin of Λ ( s λ ) is also shown to be well-polarized. These spin-oriented hypernuclear states useful for spectroscopic studies of hypernuclei such as electromagnetic moments and weak decays.

Production of polarized hypernuclei in the (K−, π−) reaction in the GeV/c region

Abstract It is shown that the (K − , π − ) reaction in the GeV / c momentum region is able to yield large spin polarizations. Cross sections and polarizations are evaluated for a typical example of 12 C(K − , π − ) Λ 12 C at p K =1.1and1.5GeV/c, where the polarizations of the elementary process are maximally positive, respectively. In addition to the ( π + ,K + ) reaction, the (K − , π − ) reaction in the GeV/ c region can be used as another powerful means to produce polarized Λ-hypernuclei, when higher intensity K − beams become available.

Highly sensitive radon monitor and radon emanation rates for detector components

Abstract The radon emanation rates for materials were measured by using the electrostatic precipitation method as a radon monitor. It was found that a low level of radon was emanated from several material components in ELEGANT V. The radon monitor has been developed for the highly sensitive measurements of low-level radon concentration. The system was shown to have a sensitivity to radon concentrations as low as 1.6 mBq / m 3 for one day measurement. The system was also used as the radon concentration monitor for the gas inside the airtight box of the ELEGANT V at Oto Cosmo Observatory.

Double beta decay study of 48Ca by CaF2 scintillator

Abstract A CaF 2 scintillation detector system (ELEGANT VI) is developed to search for neutrinoless double beta decay (0νDBD) of 48 Ca. No events were observed around the Q -value energy region after the analysis of 4.23 kg yr data. To derive the lower limit for the half-life, the expected number of background events was estimated by a Monte Carlo simulation using the measured activities of 214 Bi and 220 Rn inside CaF 2 crystals. A new lower limit is obtained to be 1.8 × 10 22 yr at the 90% C.L.

Limits on Majoron emitting neutrinoless double-beta decay of 100Mo

Abstract The single Majoron emitting neutrinoless double beta decay (0 νββB ) of 100 Mo was studied by means of ELEGANTxa0V. Axa0stringent lower limit on the half life was obtained as T 1/2 0 νββB >5.8(11)×10 21 xa0yr at 90% (68%)xa0C.L. The limit on the coupling constant |〈 g B 〉| was discussed in terms of the several nuclear models. The limit lies between 6.3×10 −5 and 3.6×10 −3 .

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.

Structure of Λ13C hypernucleus studied by the (K−, π−γ) reaction

Abstract The BNL-AGS/E929 experiment was carried out to study energy levels of the Λ 13 C hypernucleus by a gamma-ray spectroscopy. Energy splitting of the spin-orbit doublets, 1 2 − and 3 2 − states, was estimated precisely. The excitation energy of the 1st 3 2 + state was also measured. We discuss the symmetric and the anti-symmetric spin-orbit interactions between a Λ particle and a nucleon from the measurement.

PRODUCTION OF NEUTRON-RICH LAMBDA HYPERNUCLEI AT J-PARC

We discuss the usefulness of the double charge-exchange reactions (DCX) for the production of the neutron-rich Λ-hypernuclei. We believe the (π-, K+) reaction is one of the most promising DCX reactions, and propose to produce the neutron-rich Λ-hypernuclei, and , at the J-PARC 50 GeV PS by the reaction (J-PARC E10 experiment). The design of the experiment is presented.