Spectroscopy of medium-heavy Λ hypernuclei via the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow><mml:mrow><mml:msup><mml:mrow><mml:mo>,</mml:mo><mml:mi>K</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow><mml:mo>)</mml:mo></mml:math>reaction

Excitation energy spectra of ${}_{\mathrm{\ensuremath{\Lambda}}}^{89}\mathrm{Y},$ ${}_{\mathrm{\ensuremath{\Lambda}}}^{51}\mathrm{V},$ and ${}_{\mathrm{\ensuremath{\Lambda}}}^{12}\mathrm{C}$ have been measured via the $({\ensuremath{\pi}}^{+}{,K}^{+})$ reaction by using the SKS spectrometer at the K6 beam line in the KEK 12-GeV Proton Synchrotron. In the ${}_{\mathrm{\ensuremath{\Lambda}}}^{89}\mathrm{Y}$ 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 \ensuremath{\Lambda} hypernuclear systems and precisely obtaining a series of \ensuremath{\Lambda} single-particle energies in the very wide excitation energy range of more than 20 MeV, for the first time. Also in the ${}_{\mathrm{\ensuremath{\Lambda}}}^{51}\mathrm{V}$ spectrum, a similar structure to that of ${}_{\mathrm{\ensuremath{\Lambda}}}^{89}\mathrm{Y}$ was observed. In the ${}_{\mathrm{\ensuremath{\Lambda}}}^{12}\mathrm{C}$ 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.