Determination of the Michel parameters ρ, ξ, and δ in τ-lepton decays with τ→ρν tags

Using the ARGUS detector at the e(+)e(-) storage ring DORIS II, we have measured the Michel parameters rho,xi, and xi delta for tau(+/-) --> l (+/-) v (v) under bar decays in tau-pair events produced at center of mass energies in the region of the tau resonances. Using tau(-/+) --> rho(-/+) v as spin analyzing tags, we find rho(e) = 0.68 +/- 0.04 +/- 0.08, xi(e) = 1.12 +/- 0.20 +/- 0.09, xi delta(e) = 0.57 +/- 0.14 +/- 0.07, rho(mu)= 0.69 +/- 0.06 +/- 0.08, xi(mu) = 1.25 +/- 0.27 +/- 0.14 and xi delta(mu) = 0.72 +/- 0.18 +/- 0.10. In addition, we report the combined ARGUS results on rho, xi, and xi delta using this work and previous measurements. (C) 1998 Elsevier Science B.V. All rights reserved.