The most precise value for the \pi^0π0
mass was obtained from the measurement of the mass difference
m_{\pi^-}-m_{\pi^0} = 4.593\,64(48)mπ−−mπ0=4.59364(48),MeV/c^22
in the charge exchange reaction \pi^-π−p
\rightarrow \pi^0→π0n
at PSI. With the most precise charged pion mass value,
m_{\pi^+} = 139.570\,21(14)mπ+=139.57021(14),MeV/c^22
and the validity of the CPT theorem (m_{\pi^-} = m_{\pi^+}mπ−=mπ+),
a value m_{\pi^0} = 134.976\,57(50)mπ0=134.97657(50),MeV/c^22
is obtained. The measurements also revealed, for the first time,
evidence of an unexpectedly large contribution from Coulomb
de-excitation states during the pionic atom cascade.
Measurement of the charged pion mass using a low-density target of light atoms
