CHINESE ACAD SCI,INST HIGH ENERGY PHYS,BEIJING 100039,PEOPLES R CHINA
Article; Proceedings Paper
A data-driven energy scan in the immediate vicinity of tau pair production threshold has been performed using the Beijing Spectrometer (BES) at the Beijing Electron-Positron Collider (BEPC). Approximately 5 pb(-1) of data, distributed over twelve scan points, have been collected. An initial tau lepton mass value, obtained using only the e mu final state, has been published. In this paper, the final BES result on the mass measurement, based on the combined data samples of ee, e mu, e pi, eK, mu mu, mu pi, mu K, pi pi and pi K events, is presented. A maximum likelihood fit yields the value m(tau) = 1776.96(-0.19 -0.16)(+0.18 +0.20) MeV. (2) Using the data collected at the center-of-mass energy 4.03 GeV, the decay tau(-) --> nu(tau) + 3 charged pseudoscalars has been investigated. The branching ratios are determined to be Br(tau(-) --> alpha(1) nu(tau) --> rho(0) pi(+/-)nu(tau), rho(0) --> pi(+)pi(-))=(7.3+/-0.5)%, Br(tau(-) --> K*(+/-)nu(tau) --> K-s(0) pi(+/-)nu(tau), K-s(0) --> pi(+)pi(-)) = (6.0+/-1.5) x 10(-3). The decay channels with kaon have also been studied. (3) The braching ratio of psi(2s) --> tau(+)tau(-) has been determined as (3.69+/-0.71+/-0.66) x 10(-3) in the first time.