New High-Accuracy Measurement of the Pionic Mass

The pionic x-ray energies of the $4f-3d$ transition in $\pi$-P and the $5f-4d$ transition in $\pi$-Ti were measured with a bent-crystal spectrometer at the Nevis synchrocyclotron; and a new value of the pionic mass is deduced to be 139 567.5±0.9 keV, leading to an improved value for the $\mu$-neutrino mass of ${m_{{\nu }_{\mu }}}^2$=0.102±0.119 ${\mathrm{MeV}}^2$; $m_{{\nu }_{\mu }}<0.52\mathrm{}$ MeV, at 90% confidence level.