T. Endo

The (π+,K+) reaction and light Λ hypernuclear spectroscopy

Abstract High-quality excitation-energy spectra of Λ 7 Li, Λ 9 Be, Λ 13 C and Λ 16 O as well as Λ 12 C have been obtained with 2 MeV (FWHM) resolution and good statistics through the (π + ,K+) reaction. The spectra of Λ 12 C, Λ 16 0 and Λ 13 C are discussed in relation to the ΛN spindependent interaction, and those of Λ 9 Be and Λ 7 Li within the framework of the cluster structure of Λ hypernuclei. It is emphasized that Λ hypernuclear spectroscopy provides us with valuable information on Λ hypernuclear structure and the ΛN interaction.

Σ-nucleus potential studied with the (π-, K+) reaction on medium-to-heavy nuclear targets

In order to study the Sigma-nucleus optical potential, we measured inclusive (pi^-,K^+) spectra on medium-to-heavy nuclear targets: CH_2, Si, Ni, In and Bi. The CH_2 target was used to calibrate the excitation energy scale by using the elementary process p + pi^- -> K^+ + Sigma^-, where the C spectrum was also extracted. The calibration was done with +-0.1 MeV precision. The angular distribution of the elementary cross section was measured, and agreed well with the previous bubble chamber data, but with better statistics, and the magnitudes of the cross sections of the measured inclusive (pi^-,K^+) spectra were also well calibrated. All of the inclusive spectra were found to be similar in shape at a region near to the Sigma^- binding energy threshold, showing a weak mass-number dependence on the magnitude of the cross section. The measured spectra were compared with a theoretical calculation performed within the framework of the Distorted Wave Impulse Approximation (DWIA). It has been demonstrated that a strongly repulsive \sig-nucleus potential with a non-zero size of the imaginary part is required to reproduce the shape of the measured spectra.

Structure of a Λ-hypernucleus Λ89Y measured with the SKS spectrometer

Abstract We have measured an excitation energy spectrum of a Λ-hypernucleus Λ 89 Y via the ( π + , K + ) reaction by using the SKS spectrometer at KEK. The best quality data with the energy resolution of 1.63 MeV(FWHM) was obtained in the highest statistics so far. In the spectrum, we can find a splitting of the f-orbital of a Λ particle with the separation of 1.6±0.15 MeV(statistical error only), which may be attributed to the spin-orbit splitting.

Study of the Sigma-nucleus potential by the (pi-, K+) reaction on medium-to-heavy nuclear targets

In order to study the Sigma-nucleus optical potential, we measured inclusive (pi^-,K^+) spectra on medium-to-heavy nuclear targets: CH_2, Si, Ni, In and Bi. The CH_2 target was used to calibrate the excitation energy scale by using the elementary process p + pi^- -> K^+ + Sigma^-, where the C spectrum was also extracted. The calibration was done with +-0.1 MeV precision. The angular distribution of the elementary cross section was measured, and agreed well with the previous bubble chamber data, but with better statistics, and the magnitudes of the cross sections of the measured inclusive (pi^-,K^+) spectra were also well calibrated. All of the inclusive spectra were found to be similar in shape at a region near to the Sigma^- binding energy threshold, showing a weak mass-number dependence on the magnitude of the cross section. The measured spectra were compared with a theoretical calculation performed within the framework of the Distorted Wave Impulse Approximation (DWIA). It has been demonstrated that a strongly repulsive \sig-nucleus potential with a non-zero size of the imaginary part is required to reproduce the shape of the measured spectra.

Spectroscopy of light Λ hypernuclei

We recently measured high-statistics and high-resolution spectra of p-shell Λ hypernuclei produced by the (π+, K+) reaction. In this article, cross sections and their angular distributions of Λ12C and Λ16O are reported. The obtained cross sections are well reproduced by DWIA calculations.

{sigma}-nucleus potential studied with the ({pi}{sup -},K{sup +}) reaction on medium-to-heavy nuclear targets

In order to study the Sigma-nucleus optical potential, we measured inclusive (pi^-,K^+) spectra on medium-to-heavy nuclear targets: CH_2, Si, Ni, In and Bi. The CH_2 target was used to calibrate the excitation energy scale by using the elementary process p + pi^- -> K^+ + Sigma^-, where the C spectrum was also extracted. The calibration was done with +-0.1 MeV precision. The angular distribution of the elementary cross section was measured, and agreed well with the previous bubble chamber data, but with better statistics, and the magnitudes of the cross sections of the measured inclusive (pi^-,K^+) spectra were also well calibrated. All of the inclusive spectra were found to be similar in shape at a region near to the Sigma^- binding energy threshold, showing a weak mass-number dependence on the magnitude of the cross section. The measured spectra were compared with a theoretical calculation performed within the framework of the Distorted Wave Impulse Approximation (DWIA). It has been demonstrated that a strongly repulsive \sig-nucleus potential with a non-zero size of the imaginary part is required to reproduce the shape of the measured spectra.

High-Resolution Gamma-Spectroscopy of Λ 7 Li and Λ 9 Be

We report on the first two experiments of hypernuclear γ-ray spectroscopy with Hyperball, a large-acceptance germanium detector system. In a KEK experiment, we observed two γ transitions in Λ 7 Li, the spin- flip M1(3/2+ → 1/2+) at 691.7 ± 0.6 stat ± 1.0 sys keV and the E2(5/2+ → 1/2+) at 2050.4 ± 0.4 stat ± 0.7 sys keV. The former gives unambiguous information on the strength of the ΛN spin-spin interaction. B(E2) of the latter transition was measured to be \( 3.6 \pm {0.5^{stat}}\,_{ - 0.4}^{ + 0.5}{\,^{sys}}{e^2}f{m^4} \). In the second experiment at BNL, we observed the E2(5/2+, 3/2+ → 1/2+) transitions of Λ 9 Be at around 3.05 MeV.

Structure of light Λ hypernuclei and the ΛN interaction

Abstract Light Λ hypernuclear structure has been investigated through the (π + , K + ) reaction with use of the SKS spectrometer. Preliminary excitation energy spectra of Λ 7 Li, Λ 9 Be, Λ 13 C and Λ 16 O have been measured in the KEK-PS E336 experiment. The spectra of Λ 12 C and Λ 16 O were discussed in view of the ΛN interaction. It was shown that the high-quality Λ hypernuclear spectra provide us with a valuable mean for the investigation of the ΛN interaction.