J. L. Gutiérrez Santiago

arXiv2026

Semileptonic $D_{e4}$ decays: hadronic dynamics and the determination of $|V_{cs}|$

The four-body decays $D^+ \to K^-π^+e^+ν_e$ ($D_{e4}^+$) and $D^0\to \overline{K^0}π^-e^+ν_e$ ($D^0_{e4}$) are studied in a model where the momentum-dependence of the hadronic matrix elements are described in terms of $K^*(892)$ and $D^*(2010)$ pole contributions. From fits to the recent data of the BESIII collaboration we find that the $D^*$-pole can mimic the effect of the $S$-wave contribution of the $Kπ$ system to the branching fraction. Implications for the determination of the $|V_{cs}|$ quark mixing matrix element are discussed.

hep-ph↗

arXiv2020

Lepton-pair production in di-pion $τ$ lepton decays

We study the $τ^- \to ν_τ π^{-}π^{0}\ell^{+}\ell^{-}$ ($\ell=e,\,μ$) decays, which are $O(α^2)$-suppressed with respect to the dominant di-pion tau decay channel. Both the inner-bremsstrahlung and the structure- (and model-)dependent contributions are considered. In the $\ell=e$ case, structure-dependent effects are $\mathcal{O}(1\%)$ in the decay rate, yielding a clean prediction of its branching ratio, $2.3\times10^{-5}$, measurable with BaBar or Belle(-II) data. For $\ell=μ$, both contributions have similar magnitude and we get a branching fraction of $(1.6\pm0.3)\times10^{-7}$, reachable by the end of Belle-II operation. These decays allow to study the dynamics of strong interactions with simultaneous weak and electromagnetic probes; their knowledge will contribute to reducing backgrounds in lepton flavor/number violating searches.

hep-ph↗