Determinations of VusVus using inclusive hadronic ττ decay data
Abstract
Two methods for determining |Vus||Vus| employing inclusive hadronic ττ decay data are discussed. The first is the conventional flavor-breaking sum rule determination whose usual implementation produces results ∼3σ∼3σ low compared to three-family unitary expectations. The second is a novel approach combining experimental strange hadronic ττ distributions with lattice light-strange current–current two-point function data. Preliminary explorations of the latter show the method promises |Vus||Vus| determinations competitive with those from Kℓ3Kℓ3 and Γ[Kμ2]/Γ[πμ2]Γ[Kμ2]/Γ[πμ2]. For the former, systematic issues in the conventional implementation are investigated. Unphysical dependences of |Vus||Vus| on the choice of sum rule weight, ww, and upper limit, s0s0, of the weighted experimental spectral integrals are observed, the source of these problems identified and a new implementation which overcomes these problems developed. Lattice results are shown to provide a tool for quantitatively assessing truncation uncertainties for the slowly converging D=2D=2 OPE series. The results for |Vus||Vus| from this new implementation are shown to be free of unphysical ww- and s0s0-dependences, and ∼0.0020∼0.0020 higher than those produced by the conventional implementation. With preliminary new KπKπ branching fraction results as input, we find |Vus||Vus| in excellent agreement with that obtained from Kℓ3Kℓ3, and compatible within errors with expectations from three-family unitarity.