arXiv subjects

S. Okada

Publications and source records attributed to S. Okada.

60 records · Page 4Linked to original sources

arXiv2004

Neutron and proton energy spectra from the non-mesonic weak decays of 5_Lambda-He and 12_Lambda-C

We have simultaneously measured the energy spectra of neutrons and protons emitted in the non-mesonic weak decays of 5_Lambda-He and 12_Lambda-C hypernuclei produced via the (pi^+,k^+) reaction with much higher statistics over those of previous experiments. The neutron-to-proton yield ratios for both hypernuclei at a high energy threshold (60 MeV) were approximately equal to two, which suggests that the ratio of the neutron- and proton-induced decay channels, Gn(Lambda n -> nn)/Gp(Lambda p -> np), is about 0.5. In the neutron energy spectra, we found that the yield of the low-energy component is unexpectedly large, even for 5_Lambda-He.

nucl-ex↗

arXiv2004

Measurement of the $π^-$ decay width of $^5_Λ$He

We have precisely measured $Λ\to pπ^-$ decay width of \5LHe and demonstrated significantly larger $α$ -$Λ$ overlap than expected from the central repulsion $α$-$Λ$ potential, which is derived from YNG Λ$-nucleon interaction.

nucl-ex↗

arXiv2004

pi^0 decay branching ratios of 5_Lambda-He and 12_Lambda-C hypernuclei

We precisely measured pi^0 branching ratios of 5_Lambda-He and 12_Lambda-C hypernuclei produced via (pi^+,k^+) reaction. Using these pi^0 branching ratios with the pi^- branching ratios and the lifetimes, we obtained the pi^0 decay widths and the non-mesonic weak decay widths at high statistics with the accuracy of ~5 % (stat) for both hypernuclei.

nucl-ex↗

arXiv2004

Proton asymmetry in non-mesonic weak decay of light hypernuclei

We have obtained the decay asymmetry parameters in non-mesonic weak decay of polarized Lambda-hypernuclei by measuring the proton asymmetry. The polarized Lambda-hypernuclei, 5_Lambda-He, 12_Lambda-C, and 11_Lambda-B, were produced in high statistics via the (pi^+,k^+) reaction at 1.05 GeV/c in the forward angles. Preliminary analysis shows that the decay asymmetry parameters are very small for these s-shell and p-shell hypernuclei.

nucl-ex↗

arXiv2004

Dielectric responses of the layered cobalt oxysulfide Sr_2Cu_2CoO_2S_2 with CoO_2 square-planes

We have studied the dielectric responses of the layered cobalt oxysulfide Sr$_2$Cu$_2$CoO$_2$S$_2$ with the CoO$_2$ square-planes. With decreasing temperature below the Néel temperature, the resistivity increases like a semiconductor, and the thermopower decreases like a metal. The dielectric constant is highly dependent on temperature, and the dielectric relaxation is systematically changed with temperature, which is strongly correlated to the magnetic states. These behaviors suggest that carriers distributed homogeneously in the paramagnetic state at high temperatures are expelled from the antiferromagnetically ordered spin domain below the Néel temperature.

cond-mat.mtrl-sci↗

arXiv2000

The Hypergraphite: A possible extension of graphitic network

We propose a class of networks which can be regarded as an extension of the graphitic network. These networks are constructed so that surface states with non-bonding character (edge states) are formed in a tight-binding model with one orbital for each atomic site. Besides, for several networks, the tight-binding electronic structures become a zero-gap semiconductor. These properties have been found in the $π$-electron system of the graphene. Thus, we call these networks hypergraphite.

cond-mat.mtrl-sci↗