Searches for a narrow resonance in the pppi- system

The pp pi system whose quantum numbers may assume values that are forbidden for the NN system is investigated for the first time in the reaction pp --> pp pi(-)pi(+). The experiment was performed at ITEP (Moscow). The invariant-mass distribution of the pp pi(-) system reveals a resonance enhancement at M approximate to 2.06 GeV with a width about 10 MeV. The observed enhancement may signal the formation of a resonance state predicted by quark models and required for interpreting data on low-energy pion-nucleus scattering accompanied by double charge exchange.