Speaker
Description
Bound states caused by attractive $\bar{K}N (I=0)$ interaction, such as $\Lambda(1405)$ and kaonic nuclei, are interesting systems with strangeness.
Many experimental attempts have tried to establish an existence of the lightest kaonic nuclei, "$K^- pp$". However, no clear conclusion was reached. Recently, J-PARC E15 collaboration searched for "$K^- pp$", using the in-flight $K^- +^3\text{He}$ reaction with an exclusive analysis of the $\Lambda p n$ final state. By reconstructing not only the $\Lambda p$ invariant-mass but also the momentum transfer to the $\Lambda p$ system, they definitely showed event concentration interpretted as "$K^- pp$" bound state with $B.E.=42 \pm3(\text{stat})^{+3}_{-4}(\text{syst})$ MeV and $\Gamma =100 \pm 7(\text{stat})^{+19}_{-9}(\text{syst})$. Moreover, small spatial size of "$K^- pp$" is implied, which supports theoretical predictions that a high-density nuclear matter is realized in heavier kaonic nuclei.
In order to expand this successful experimental method to heavier kaonic nuclei, such as $\bar{K}NNN, \bar{K}NNNN, \dots$, and detailed study for fundamental properties of the $\bar{K}NN$ state, we are developping a new magnetic spectrometer.
Because an exclusive analysis requires detections of decay particles from the kaonic nuclei as many as possible, the new spectrometer will have larger solid angle of 93%. To realize it, superconducting a sorenoid magnet and some detectors, a cylindrical drift chamber and charged particle/neutron counters, are 3-4 meters long. Detection efficiencies for neutron would be improved at least 1.7 times better than that of the current spectrometer.