Hypernuclear decay pion spectroscopy at MAMI-C

Measurements of absolute binding energies of hypernuclei contribute to a comprehensive understanding of the interaction between nucleons and hyperons (YN interaction). Hypernuclear decay-pion spectroscopy is devised as a new method to deduce the absolute binding energy of light hypernuclei with an accuracy of -30 keV. The first feasibility experiment was performed in 2011 and the second experiment was performed in 2012 using the high intensity electron beam of the Mainz Microtron C (MAMI-C). We successfully identified the pionic decay events from 4 \λH using a positron absorber in the second experiment. However, as continuous pion background events from quasifree hyperons cannot be negligible, we learned that a collimator should be installed around the beam target to suppress the background events. We expect to suppress 70% background using the collimator. The next experiment is planed in early summer of 2014.