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

Abstract

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 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 Be(π − , π + ) 9 He (g.s.).