Abstract
Lepton Flavour Universality tests with semileptonic Λb → Λ * c decays are important to corroborate the present anomalies in the similar ratios \( {R_D}_{{}^{\left(\ast \right)}} \), and can provide complementary constraints on possible origins of these anomalies beyond the Standard Model. In this paper we provide — for the first time — all the necessary theoretical ingredients to perform and interpret measurements of \( {R}_{\Lambda_c^{*}} \) at the LHCb experiment. For this, we revisit the heavy-quark expansion of the relevant hadronic matrix elements, and provide their expressions to order αs and 1/m accuracy. Moreover, we study the sensitivity to the form factor parameters given the projected size and purity of upcoming and future LHCb datasets of \( {\Lambda}_b\to {\Lambda}_c^{*}\mu \overline{\nu} \) decays. We demonstrate explicitly the need to perform a simultaneous fit to both Λ * c final states. Finally, we provide projections for the uncertainty of \( {R}_{\Lambda_c^{*}} \) based on the form factors analysis from semimuonic decays and theoretical relations based on the heavy-quark expansion.
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Böer, P., Bordone, M., Graverini, E. et al. Testing lepton flavour universality in semileptonic Λb → Λ * c decays. J. High Energ. Phys. 2018, 155 (2018). https://doi.org/10.1007/JHEP06(2018)155
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DOI: https://doi.org/10.1007/JHEP06(2018)155