New measurement of the pi - -meson mass

We measured the energies of the ..pi..-mesic-atom 4f-3d transitions in Ti and Ca, equal respectively to 87 649.2 +- 1.9 and 72 347.0 +- 1.1 eV. The normal value was taken to be the K/sub alpha//sub 1/W energy from the ..beta.. decay of /sup 182/Ta: 59 318.77 +- 0.21 eV. Using the conversion factors given in /sup //sup 1//sup /, we found for the rest mass of the ..pi../sup -/ meson the value M/sub pi/-c/sup 2/=139 565.7 +- 1.7 keV. (AIP)