The ρ-mass, width and line shape in [formula omitted] annihilation at rest into π+π−π0

Abstract

A high-statistics data sample on p ̄ p→π +π −π 0 is studied to deduce the mass, width, and line shape of charged and neutral ρ mesons. We find that the line shape is well described by a relativistic Breit-Wigner function. We find mass degeneracy of the ρ ± and ρ 0 masses when mixing with the ω in its π + π − decay mode is taken into account. A fit with one mass and width for the three ρ charge states yields m ρ =(763.0±1.3) MeV and Γ ρ =(149.5±1.3) MeV. The mass difference between charged and neutral ρ 's is determined to be (1.6±0.6±1.7) MeV. A possible influence on the ρ mass due to the isobar approximation is discussed.