Measurement of the spectral functions of vector current hadronic tau decays

A measurement of the spectral functions of non-strange vector current final states is presented, using 124 358 pairs recorded by the ALEPH detector at LEP during the years 1991 to 1994. The spectral functions of the dominant two- and four-pion decay channels are compared to published results of e+e− annihilation experiments via isospin rotation. A combined fit of the pion form factor from decays and e+e− data is performed using different parametrizations. The mass and the width of the (770) and the 0(770) are separately determined in order to extract possible isospin violating effects. The mass and width differences are measured to be M(770)−M0(770)=(0010) MeV/c2 and (770)−0(770)=(0119) MeV/c2.