Measurement of the ω→π+π−π0 Dalitz plot distribution

Abstract

Using the production reactions p d → He 3 ω and p p → p p ω , the Dalitz plot distribution for the ω → π + π − π 0 decay is studied with the WASA detector at COSY, based on a combined data sample of ( 4.408 ± 0.042 ) × 10 4 events. The Dalitz plot density is parametrised by a product of the P -wave phase space and a polynomial expansion in the normalised polar Dalitz plot variables Z and ϕ . For the first time, a deviation from pure P -wave phase space is observed with a significance of 4.1 σ . The deviation is parametrised by a linear term 1 + 2 α Z , with α determined to be + 0.147 ± 0.036 , consistent with the expectations of ρ -meson-type final-state interactions of the P -wave pion pairs.