Tau Polarimetry with Inclusive Decays

Abstract

The spin asymmetry parameter $A_{\tau }$ characterizing the angular distribution of the total hadron momentum in the decay of a polarized tau can be calculated rigorously using perturbative QCD and the operator product expansion. Perturbative QCD corrections to the free quark result $A_{\tau }=1/3$ can be expressed as a power series in ${\alpha }_s(M_{\tau })$ and nonperturbative QCD corrections can be expanded systematically in powers of $1/M_{\tau }^2$. The QCD prediction is $A_{\tau }=0.41\pm 0.02$. In the decay of a high energy tau into hadrons, the value of the hadronic energy distribution $d{R}_{\tau }/dz$ evaluated at the maximum hadronic energy fraction $z=1$ can also be calculated rigorously from QCD.

Comments: LateX, 11 pages, no figures, NUHEP-TH-93-5