Upper limit of the muon-neutrino mass and charged-pion mass from momentum analysis of a surface muon beam

We have determined the momentum p(mu+) of muons from the decay pi(+)-->mu(+)nu(mu) at rest, by analyzing a surface muon beam in a magnetic spectrometer equipped with a silicon microstrip detector. The rest p(mu+)=(29.792 00+/-0.000 11) MeV/c leads to a squared muon-neutrino mass of m(nu mu)(2)=(-0.016+/-0.023) MeV(2), which corresponds to a ''laboratory'' upper limit of 0.17 MeV (C.L.=0.9) for the muon-neutrino mass. The cosmological upper limit of the neutrino mass (65 eV), the muon mass, and the new value of p(mu+) yield the pion mass m(pi+)=(139.570+/-0.000 14) MeV. Alternatively, if one does not use the cosmological upper limit of m(nu mu), then a combined fit including the new p(mu+) value, and the m(mu+) and m(pi-) values from other experiments and the CPT theorem (m(pi+)=m(pi-)) leads to m(pi+/-)=(139.570 37+/-0.000 21) MeV. As a side result, the mean kinetic energy of the pions stopped in the production target, made of isotropic graphite, immediately before their decay is found to be <(T-pi+)over bar>=(0.425+/-0.016) eV. This is consistent with the hypothesis that the pions are trapped in the potential well of a spherical harmonic oscillator, V(r)=V-0+1/2k(s)r(2), with k(s)=(1.144+/-0.088)X10(17) eV/cm(2).