Precise measurement of hadronic τ-decays with an η meson

Studies ofτ−→ηK−ντandτ−→ηπ−Sanchez1, Lees2, Poireau3 et al. 2011Phys. Rev. D35070View full textAdd to dashboardCite

“…The measurement is compatible with the world average of (1.61 ± 0.11) × 10 −4 , which is dominated by the Belle measurement of (1.58 ± 0.05 ± 0.09) × 10 −4 [5]; this Belle measurement used the η → γγ and the η → π + π − π 0 decay modes (a branching fraction of (1.60 ± 0.15 ± 0.10) × 10 −4 is reported from the η → π + π − π 0 decay mode alone). The Belle Collaboration suggest that previous τ − → ηK − ν τ measurements [3,4] underestimated background contamination, an assertion that is supported by the observation that the Belle and BABAR results are in good agreement.…”

“…The τ − → ηK − ν τ branching fraction has previously been measured by the CLEO [3], ALEPH [4] and Belle [5] Collaborations, giving a world average value of B(τ − → ηK − ν τ ) = (1.61 ± 0.11) × 10 −4 [6]. The measurement of B(τ − → ηK − ν τ ) reported here is the first from the BABAR experiment, and its consistency with the Particle Data Group (PDG) value helps to validate the method used for the τ − → ηπ − ν τ analysis.…”

τ − →K − η (′) ν τ decays in Chiral Perturbation Theory with resonances

“…[76][77][78] (for the strangeness-changing form factors) 7 and [95,96] (for the strangeness-conserving ones) unitarizing SU (3) and U (3) (respectively) χP T with explicit exchange of resonances [97]. However, given the large errors of the τ − → K − ην τ decay spectra measured by the BaBar [42] and Belle [41] Collaborations and the absence of data on the K − η channel we consider that it is not timely to perform such a cumbersome numerical analysis in the absence of enough experimental guidance 8 . For this reason we have attempted to obviate the inherent inelasticity of the Kη ( ) channels and tried an elastic description, where the form factor that defines the input phaseshift is given by eq.…”

“…Only very recently Belle [41] and BaBar [42] managed to improve these measurements reducing the branching fraction to essentially half of the CLEO and ALEPH results and achieving a decrease of the error at the level of one order of magnitude. Belle [41] measured a branching ratio of (1.58±0.05±0.09)·10 −4 and BaBar [42] (1.42±0.11±0.07)·10 −4 , which combined to give the PDG average (1.52±0.08)·10 −4 [43]. The related decay τ − → K − η ν τ has not been detected yet, although an upper limit at the 90% confidence level was placed by BaBar [44].…”

“…Belle's paper [41] cites the few existing calculations of the τ − → K − ην τ decays based on Chiral Lagrangians [45][46][47][48] and concludes that 'further detailed studies of the physical dynamics in τ decays with η mesons are required' (see also, e.g. Ref.…”