First Measurement of the Branching Fraction of the Decay psi(2S) --> Tau+Tau-

摘要

The branching fraction of the psi(2S) decay into gamma (sup +) gamma (sup -) has been measured for the first time using the BES detector at the Beijing Electron-Positron Collider. The result is B(sub gamma gamma) = (2.71 plus or minus 0.43 plus or minus 0.55) X 10 to the minus 3 power, where the first error is statistical and the second is systematic. This value, along with those for the branching fractions into e (sup +) e (sup -) and mu (sup +) mu (sup -) of this resonance, satisfy well the relation predicted by the sequential lepton hypothesis. Combining all these values with the leptonic width of the resonance, the total width of the psi(2S) is determined to be (252 plus or minus 37) keV.