Improved description of dilepton production in τ − → ντP− decays
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Adolfo Guevara, Gabriel López Castro, and Pablo Roig. Improved description of dilepton production in τ − → ντP− decays. Phys. Rev. D 105, 076007 [DOI: 10.1103/PhysRevD.105.076007]
SponsorshipCiencia de Frontera Conacyt 162336, 428218; Cátedras Marcos Moshinsky; SEP-Cinvestav Fund 142, MCIN/AEI/10.13039/501100011033, PID2020–114473 GB-I00; Fundación Marcos Moshinsky 319395; Consejo Nacional de Ciencia y Tecnología; Ministerio de Economía y Competitividad; Generalitat Valenciana Prometeo/2017/053; European Regional Development Fund FIS2017-85053-C2-1-P; Junta de Andalucía FQM-225
Recently, the Belle Collaboration reported the first measurements of the τ−→ντπ−e+e− branching fraction and the spectrum of the pion-dielectron system. In an analysis previous to Belle’s results, we evaluated this branching fraction which turned out to be compatible with that reported by Belle, although with a large uncertainty. This is the motivation to seek for improvement on our previous evaluation of τ−→ντπ−ℓ+ℓ− decays (ℓ=e, μ). In this paper we improve our calculation of the WP−γ∗ vertex by including flavor-symmetry breaking effects in the framework of the resonance chiral theory. We impose QCD short-distance behavior to constrain most parameters and data on the π−e+e− spectrum reported by the Belle Collaboration to fix the remaining free ones. As a result, improved predictions for the branching ratios and hadronic/leptonic spectra are reported, which are in good agreement with observations. Analogous calculations for the strangeness-changing τ−→ντK−ℓ+ℓ− transitions are reported for the first time. Albeit one expects the mπμ+μ− spectrum to be measured in Belle-II and the observables with ℓ=e can be improved, it is rather unlikely that the K channels can be measured due to the suppression factor |Vud/Vus|2=0.05.