An azimuthal asymmetry in the pion from tau decays in specific neutrino-hyperon processes provides a CP-odd signal for beyond-Standard-Model physics encoded in dimension-six operators.
Precise predictions for $\Lambda_b \to \Lambda_c$ semileptonic decays
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abstract
We calculate the $\Lambda_b \to \Lambda_c \ell \nu$ form factors and decay rates for all possible $b\to c \ell\bar\nu$ four-Fermi interactions beyond the Standard Model, including nonzero charged lepton masses and terms up to order $\alpha_s\, \Lambda_\text{QCD}/m_{c,b}$ and $\Lambda_\text{QCD}^2/m_c^2$ in the heavy quark effective theory. At this order, we obtain model independent predictions for semileptonic $\Lambda_b \to \Lambda_c$ decays in terms of only two unknown sub-subleading Isgur-Wise functions, which can be determined from fitting LHCb and lattice QCD data. We thus obtain model independent results for $\Lambda_b\to \Lambda_c\ell\bar\nu$ decays, including predictions for the ratio $R(\Lambda_c) = {\cal B}(\Lambda_b\to \Lambda_c \tau\bar\nu) / {\cal B}(\Lambda_b\to \Lambda_c \mu\bar\nu)$ in the presence of new physics, that are more precise than prior results in the literature, and systematically improvable with better data on the decays with $\mu$ (or $e$) in the final state. We also explore tests of factorization in $\Lambda_b \to \Lambda_c\pi$ decays, and emphasize the importance of measuring at LHCb the double differential rate $d^2\Gamma(\Lambda_b\to\Lambda_c\ell\bar\nu) / (d q^2\, d\cos\theta)$, in addition to the $q^2$ spectrum.
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hep-ph 3years
2026 3roles
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Sum rules for b→cτν transitions to orbitally excited charm hadrons show larger deviations from heavy quark symmetry than ground states, with tensor effects often sizable, but current form factor uncertainties prevent robust lepton-universality predictions.
A sum rule among LFU ratios R^{mu e} for c to d l nu decays holds within 1% under current NP bounds, yielding a prediction for the unmeasured R_n^{mu e} in Lambda_c to n l nu.
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Probing New Physics and CP Violation in $\nu_\tau n \to \Lambda_c \tau^- (\pi^- \nu_\tau)$ and $\bar\nu_\tau p \to \Lambda \tau^+ (\pi^+ \bar\nu_\tau)$
An azimuthal asymmetry in the pion from tau decays in specific neutrino-hyperon processes provides a CP-odd signal for beyond-Standard-Model physics encoded in dimension-six operators.
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$b \to c$ semileptonic sum rule: orbitally excited hadrons
Sum rules for b→cτν transitions to orbitally excited charm hadrons show larger deviations from heavy quark symmetry than ground states, with tensor effects often sizable, but current form factor uncertainties prevent robust lepton-universality predictions.
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Semileptonic sum rules in heavy-to-light charm decays
A sum rule among LFU ratios R^{mu e} for c to d l nu decays holds within 1% under current NP bounds, yielding a prediction for the unmeasured R_n^{mu e} in Lambda_c to n l nu.