Optimized lepton universality tests in $$B\rightarrow V \ell {\bar{\nu }}$$ decays
Gino Isidori (Physik-Institut, Universität Zürich, Zurich, 8057, Switzerland); Olcyr Sumensari (Physik-Institut, Universität Zürich, Zurich, 8057, Switzerland)
We propose improved lepton flavor universality (LFU) ratios in semileptonic $$P\rightarrow V \ell {\bar{\nu }}$$ decays, when comparing $$\mu $$ and $$\tau $$ modes, that minimize the theoretical form-factor uncertainties. These optimized ratios are obtained with simple cuts or reweighting of the dilepton mass distributions, which imply a minimum loss of signal on the rare tauonic modes while maximizing the cancellation of theoretical uncertainties among the two modes. We illustrate the usefulness of these observables in $$B_c\rightarrow J/\psi $$ , $$B_c\rightarrow \psi (2S)$$ , $$B\rightarrow D^*$$ and $$B_s\rightarrow D_s^*$$ transitions, showing that in all cases we can reach $${\mathcal {O}}(1\%)$$ uncertainties on the SM predictions of the improved LFU ratios employing conservative form-factor uncertainties.