Search for Tetraneutron by Pion Double Charge Exchange Reaction at J-PARC

Tetraneutron (${}^{4}n$) has come back in the limelight, because of recent observation of a candidate resonant state at RIBF. We propose to investigate the pion double charge exchange (DCX) reaction, i.e. $^4$\mathrm{H}\mathrm{e}$({\pi}^- , {\pi}^+)$,asanalternativewaytopopulatetetraneutron\mathrm{.}Anintense${\pi}^-$ beam with the kinetic energy of ~850 MeV, much higher than that in past experiments at LAMPF and TRIUMF, will open up a possibility to improve the experimental sensitivity of the formation cross section, which will be much smaller than hitherto known DCX cross sections such as $^9$\mathrm{B}\mathrm{e}$({\pi}^-, {\pi}^+)^9$\mathrm{H}\mathrm{e}$\ (g.s.)$.