Determination of |V_us| from hadronic tau decays

Nuclear Physics B - Proceedings Supplements, 2007

Recent progress in the determination of |Vus| employing strange hadronic τ -decay data are reported. This includes using the recent OPAL update of the strange spectral function, as well as augmenting the dimension-two perturbative contribution with the recently calculated order α 3 s term on the theory side. These updates result in |Vus| = 0.2220 ± 0.0033, with the uncertainty presently being dominated by experiment, and already being competitive with the standard extraction from Ke3 decays and other new proposals to determine |Vus|. In view of the ongoing work to analyse τ -decay data at the B-factories BaBar and Belle, as well as future results from BESIII, the error on |Vus| from τ decays is expected to be much reduced in the near future. * Email: jamin@ifae.es; Invited talk given by M.

High Energy Physics, 2007

We report on recent work to determine the CKM matrix element |V us | using strange hadronic τ decay data. We use the recent OPAL update of the strange spectral function, while on the theory side we update the dimension-two perturbative contribution including the recently calculated α 3 s terms. Our result |V us | = 0.2220±0.0033 is already competitive with the standard extraction from K e3 decays and other new proposals to determine |V us |. The actual uncertainty on |V us | from τ data is dominated largely by experiment and will eventually be much reduced by B-factories and future τ -charm factory data, providing one of the most accurate determinations of this Standard Model parameter.

The European Physical Journal C, 2004

Tau lepton decays with open strangeness in the final state are measured with the OPAL detector at LEP to determine the strange hadronic spectral function of the τ lepton. The decays τ − → (Kπ) − ν τ , (Kππ) − ν τ and (Kπππ) − ν τ with final states consisting of neutral and charged kaons and pions have been studied. The invariant mass distributions of 93.4% of these final states have been experimentally determined. Monte Carlo simulations have been used for the remaining 6.6% and for the strange final states including η mesons. The reconstructed strange final states, corrected for resolution effects and detection efficiencies, yield the strange spectral function of the τ lepton. The moments of the spectral function and the ratio of strange to non-strange moments, which are important input parameters for theoretical analyses, are determined. Furthermore, the branching fractions B(τ − → K − π 0 ν τ ) = (0.471 ± 0.064 stat ± 0.022 sys )% and B(τ − → K − π + π − ν τ ) = (0.415 ± 0.059 stat ± 0.031 sys ) % have been measured.

Physical Review D, 2011

We present a new framework for the extraction of the strong coupling from hadronic τ decays through finite-energy sum rules. Our focus is on the small, but still significant non-perturbative effects that, in principle, affect both the central value and the systematic error. We employ a quantitative model in order to accommodate violations of quark-hadron duality, and enforce a consistent treatment of the higher-dimensional contributions of the Operator Product Expansion to our sum rules. Using 1998 OPAL data for the non-strange isovector vector and axial-vector spectral functions, we find the n f = 3 values α s (m 2 τ) = 0.307 ±0.019 in fixed-order perturbation theory, and 0.322±0.026 in contour-improved perturbation theory. For comparison, the original OPAL analysis of the same data led to the values 0.324 ± 0.014 (fixed-order) and 0.348 ± 0.021 (contour-improved).

1998

An analysis based on 124000 selected tau pairs recorded by the ALEPH detector at LEP provides the vector (V) and axial-vector (A) spectral functions of hadronic tau decays together with their total widths. This allows the evaluation of finite energy chiral sum rules that are weighted integrals over the (V-A) spectral functions. In addition, a precise measurement of alpha_s along

European Physical Journal C, 1997

A measurement of the spectral functions of non-strange τ vector current final states is presented, using 124 358 τ pairs recorded by the ALEPH detector at LEP during the years 1991 to 1994. The spectral functions of the dominant two- and four-pion τ decay channels are compared to published results of e +e - annihilation experiments via isospin rotation. A combined fit of the pion form factor from τ decays and e +e - data is performed using different parametrizations. The mass and the width of the ρ ±(770) and the ρ 0(770) are separately determined in order to extract possible isospin violating effects. The mass and width differences are measured to be M ρ±(770) - M ρ0(770) = (0.0 ± 1.0) MeV/c 2 and Γ ρ±(770) - Γ ρ0(770) = (0.1 ± 1.9) MeV/c 2.