Experimental study of π− π+ system at low invariant-masses

We report on results of an experiment to study the reaction π−p → π− π+ in the incident pion momentum region between 295 and 450 MeV/c. A departure from phase space was observed in invariant-mass spectra and angular distributions which cannot be explained with Δ and ϱ resonance production. It indicates aI=0,JP = 0+ π− π+ final-state interaction.