Resonant behaviour in double charge exchange reaction of π^+ mesons on the nuclear photoemulsion

Abstract

The invariant mass spectra of the $ppπ^-$ and $pp$ systems produced in the double charge exchange (DCX) of positively charged pions on photoemulsion are analysed. A pronounced peak is observed in the $ppπ^-$ invariant mass spectrum, while the $M_{pp}$ spectrum exhibits a strong Migdal-Watson effect of the proton-proton final state interaction. These findings are in favor of the $NN$-decoupled $NNπ$ pseudoscalar resonance with T=0 called $d'$.