The charged and neutral pion masses revisited.

Results from neutrino mass and oscillation experiments now set the mass of the muon neutrino to less than 2 eV/c2. This fact, together with our former measurement of the muon momentum in pion decay at rest, p μ + = (29.792 00 ± 0.000 11) MeV/c, allows us to directly determine the charged pion mass with 1 ppm precision which constitutes the most precise value of the charged pion mass to date, m π + = (139.570 21 ± 0.000 14) MeV / c 2. This value is within 1.44 σ of the Particle Data Group's compilation of the charged pion mass value, m π ± = (139.570 61 ± 0.000 24) MeV/c2. From p μ + we derive the kinetic energy of the muon, T μ + = (4.119 84 ± 0.000 03) MeV and the mass difference, m π + − m μ + = (33.911 84 ± 0.000 14) MeV/c2. From our new m π + value, assuming CPT invariance (m π − = m π + ) and our measured mass difference D π = m π − − m π 0 = (4.593 64 ± 0.000 48) MeV/c2 we obtain a new value for the neutral pion mass, m π 0 = (134.976 57 ± 0.000 50) MeV/c2. One also obtains a new quantitative measure of CPT invariance in the pion sector: (m π + − m π − ) / m π (av) = (− 2.9 ± 2.0) ⋅ 10 − 6 , an improvement by two orders of magnitude. [ABSTRACT FROM AUTHOR]