Research Papers in Physics and Astronomy


Date of this Version



Published by American Physical Society. Phys. Rev. Lett. 78, 4686 (1997). Permission to use. Copyright © 1997 American Physical Society.


We have measured the spectral shape Michel parameters ρ and η using leptonic decays of the τ, recorded by the CLEO II detector. Assuming e-μ universality in the vectorlike couplings, we find ρeμ = 0.735 ± 0.013 ± 0.008 and ηeμ = 20.015 ± 0.061 ± 0.062, where the first error is statistical and the second systematic. We also present measurements for the parameters for e and μ final states separately.

Included in

Physics Commons