Study of double-$\Lambda$ Hypernuclei at J-PARC (E07) experiment

To study double strangeness system such as double-$\Lambda$ hypernuclei and H-dibaryon, Hybrid-emulsion experiments with counter (E176) and scintillating-fiber (E373) have been performed for these twenty years. In the experiments, we have obtained nearly ten thousand events of $\Xi ^-$ hyperon capture at rest in nuclear emulsion, and observed 8 events of sequential decay of light double-$\Lambda$ hypernuclei and 5 events of twin hypernuclei. Recently, we succeeded to measure two $\Lambda$ binding energies of $6 \atop {\Lambda \Lambda}$He, $11 \atop {\Lambda \Lambda}$Be and $13 \atop {\Lambda \Lambda}$B. However, very little is known for double-strangeness system. In this talk, we present a quite improved experiment (E07 at J-PARC) with ten times' statistics of the previous experiments. A new-generation hybrid-emulsion method is applied to search for double-$\Lambda$ hypernuclei. In the experiment, we handle Double-sided Silicon Strip tracking Detector (DSSD) for precise detection of $\Xi ^-$ hyperon in the emulsion, and huge amount of emulsion gel (2.6 tons). We also develop speedy scanning system to complete scanning of 10$^6$ $\Xi ^-$ hyperons within a few years. It is expected that one million $\Xi ^-$ hyperons produce about 10$^2$ double-$\Lambda$ hypernuclear events in the emulsion. We will make a nuclear chart with double strangeness.