At the Mainz Microtron MAMI, the first high-resolution pion spectroscopy from decays of strange systems was performed by electron scattering off a 9 Be target in order to study the Λ binding energy of light hypernuclei. Positively charged kaons were detected by a short-orbit spectrometer with a broad momentum acceptance at zero degree forward angles with respect to the beam, efficiently tagging the production of strangeness in the target nucleus. In coincidence, negatively charged decay-pions were detected by two independent high-resolution spectrometers. About 10 3 pionic weak decays of hyperfragments and hyperons were observed. The pion momentum distribution shows a monochromatic peak at p π ≈ 133 MeV/c, corresponding to the unique signature for the two-body decay of hyperhydrogen 4 Λ H → 4 He + π − , stopped inside the target. Its Λ binding energy was determined to be B Λ = 2.12 ± 0.01 (stat.) ± 0.09 (syst.) MeV with respect to the 3 H + Λ mass.
A systematic study on the Λ ground state binding energy of hyperhydrogen 4 Λ H measured at the Mainz Microtron MAMI is presented. The energy was deduced from the spectroscopy of mono-energetic pions from the two-body decays
A spectroscopy of a 10 Λ Be hypernucleus was carried out at JLab Hall C using the (e, e ′ K + ) reaction. A new magnetic spectrometer system (SPL+HES+HKS), specifically designed for high resolution hypernuclear spectroscopy, was used to obtain an energy spectrum with a resolution of ∼ 0.78 MeV (FWHM). The well-calibrated spectrometer system of the present experiment using p(e, e ′ K + )Λ,Σ 0 reactions allowed us to determine the energy levels, and the binding energy of the ground state peak (mixture of 1 − and 2 − states) was obtained to be B Λ = 8.55 ± 0.07(stat.) ± 0.11(sys.) MeV. The result indicates that the ground state energy is shallower than that of an emulsion study by about 0.5 MeV which provides valuable experimental information on Charge Symmetry Breaking (CSB) effect in the ΛN interaction.
An experiment with a newly developed high-resolution kaon spectrometer (HKS) and a scattered electron spectrometer with a novel configuration was performed in Hall C at Jefferson Lab (JLab). The ground state of a neutron-rich hypernucleus,
The energy spacing between the ground-state spin doublet of 4 Λ He(1 + ,0 + ) was determined to be 1406 ± 2 ± 2 keV, by measuring γ rays for the 1 + → 0 + transition with a high efficiency germanium detector array in coincidence with the 4 He(K − , π − ) 4Λ He reaction at J-PARC. In comparison to the corresponding energy spacing in the mirror hypernucleus 4 Λ H, the present result clearly indicates the existence of charge symmetry breaking (CSB) in ΛN interaction. It is also found that the CSB effect is large in the 0 + ground state but is by one order of magnitude smaller in the 1 + excited state, demonstrating that the ΛN CSB interaction has spin dependence.
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