Search for Tetraneutron by Pion Double Charge Exchange Reaction at J-PARC
Tetraneutron ($^4n$) 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. $^4\mathrm{He}(π^- , π^+)$, as an alternative way to populate tetraneutron. An intense $π^-$ 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 $^9\mathrm{Be}(π^-, π^+)^9\mathrm{He}\ (g.s.)$.
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