Tau polarimetry with inclusive decays

Abstract

The spin asymmetry parameter A τ 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 τ = 1/3 can be expressed as a power series in α s (M τ ) and nonperturbative QCD corrections can be expanded systematically in powers of 1/M 2 τ . The QCD prediction is A τ = 0.41 ± 0.02. In the decay of a high energy tau into hadrons, the value of the hadronic energy distribution dR τ /dz evaluated at the maximum hadronic energy fraction z = 1 can also be calculated rigorously from QCD.

αs from tau decays

“…Since the original and previous theoretical works in [1]- [5] and the ALEPH measurement [6], there has been an amount of progress both theoretically and experimentally in the determination of α s from tau decays. The theoretical progress resides mainly in a better understanding of the QCD perturbative and nonperturbative contributions to the inclusive hadronic width, as discussed in recent reviews [7]- [9] while the experimental one can be essentially due to the improved measurement of the leptonic width (see e.g.…”

Comparison of the Padé Approximation Method to Perturbative QCD Calculations

“…10 Once again, as seen in the We now turn to some QCD applications of our PA approach. Let us first consider the R τ ratio 11 where R τ is defined as follows:…”

Neutral-Higgs-bosonCPviolation atμ+μ−Atwood1, Soni2 1995Phys. Rev. D513630View full textAdd to dashboardCite

“…If the r decays semileptonically, then ET = -5 [14] (note that if one could observe the fi then E = 1). In [14] it is shown that the inclusive hadronic decays of the T can give EL = -0.42 (h stands for inclusive hadron states).…”

“…If the r decays semileptonically, then ET = -5 [14] (note that if one could observe the fi then E = 1). In [14] it is shown that the inclusive hadronic decays of the T can give EL = -0.42 (h stands for inclusive hadron states). If one analyzes the detailed structure of the hadronic decays one can obtain better results [15,16] but we will just use this number in our discussions to follow.…”