Spectroscopy of medium-heavy Λ hypernuclei via the (π⁺,K⁺) reaction

Excitation energy spectra of ⁸⁹_ΛY, ⁵¹_ΛV, and ¹²_ΛC have been measured via the (π⁺, K⁺) reaction by using the SKS spectrometer at the K6 beam line in the KEK 12-GeV Proton Synchrotron. In the ⁸⁹_ΛY spectrum, obtained with an energy resolution of 1.65 MeV (FWHM) and in the highest statistics so far, we have succeeded in clearly observing a characteristic fine structure in heavy Λ hypernuclear systems and precisely obtaining a series of Λ single-particle energies in the very wide excitation energy range of more than 20 MeV, for the first time. Also in the ⁵¹_ΛV spectrum, a similar structure to that of ⁸⁹_ΛY was observed. In the ¹²_ΛC spectrum, new core-excited states were clearly resolved thanks to the best energy resolution of 1.45 MeV so far achieved by using the SKS spectrometer.