A NEW DETERMINATION OF THE PION MASS

Initial measurements concerning the feasibility of a new pion mass det ermination are described. In a first step, a high-resolution crystal s pectrometer was coupled to a cyclotron trap which provides a high pion stopping density, sufficient to check predictions for the cascade pro cess and to measure the stability of the apparatus. A comparison with the measured Cu K-alpha fluorescence line resolves an ambiguity in the value of the pion mass. The preliminary result from this experiment i s m(pi-) = (139.57040 +/- 0.00045) MeV/c(2).