A. Higashi

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.

An active segmented target for studying hypernuclear production

Abstract An active segmented carbon target has been constructed to study the production of hypernuclei and quasifree hyperons in the (π, K) reaction on 12C. It consists of 64 scintillator segments stacked along the z (beam) axis with a spatial resolution of 2 mm in the segmentation direction. The device has been employed as a live target in a (π+,K+) experiment studying polarizations and weak decays of hypernuclei. It was used to reconstruct the energy loss patterns near the reaction vertex and to investigate the reaction mechanism. An efficiency of 84% was obtained for tagging events in the Λ12C ground state region

Polarization and weak decay of Λ hypernuclei

Abstract The 12 C( π + , K + ) reaction was used to produce polarized. A hypernuclei for the first time. Asymmetries of weak decay particles were measured. In the high excitation region, where quasifree production of Λ hypersons is dominant, the polarization of Λ was derived. It is found to be consistent with that for the elementary n ( π + , K + ) Λ reaction which demonstrates that the spin characteristics of the elementary reaction is not modified by the nuclear medium. In the low excitation region, where hypernuclei are dominantly produced, asymmetries of the non-mesonic decay protons were measured. The measurement and calculated polarization gave large asymmetry parameter (−1). It will elucidate the non-mesonic decay mechanism and open a new field of hypernuclear physics.