Global fit to b → cτν transitions

Abstract

Abstract We perform a general model-independent analysis of $$ b\to c\tau {\overline{\nu}}_{\tau } $$ b → cτ ν ¯ τ transitions, including measurements of ℛ D , ℛ D∗, their q 2 differential distributions, the recently measured longitudinal D* polarization $$ {F}_L^{D\ast } $$ F L D ∗ , and constraints from the $$ {B}_c\to \tau {\overline{\nu}}_{\tau } $$ B c → τ ν ¯ τ lifetime, each of which has significant impact on the fit. A global fit to a general set of Wilson coefficients of an effective low-energy Hamiltonian is presented, the solutions of which are interpreted in terms of hypothetical new-physics mediators. From the obtained results we predict selected $$ b\to c\tau {\overline{\nu}}_{\tau } $$ b → cτ ν ¯ τ observables, such as the baryonic transition $$ {\Lambda}_b\to {\Lambda}_c\tau {\overline{\nu}}_{\tau } $$ Λ b → Λ c τ ν ¯ τ , the ratio ℛ J/ψ , the forward-backward asymmetries $$ {\mathcal{A}}_{\mathrm{FB}}^{D\left(\ast \right)} $$ A FB D ∗ , the τ polarization asymmetries $$ {\mathcal{P}}_{\tau}^{D\left(\ast \right)} $$ P τ D ∗ , and the longitudinal D* polarization fraction $$ {F}_L^{D\ast } $$ F L D ∗ . The latter shows presently a slight tension with any new-physics model, such that an improved measurement could have an important impact. We also discuss the potential change due the very recently announced preliminary $$ {\mathrm{\mathcal{R}}}_{\mathcal{D}\left(\ast \right)} $$ ℛ D ∗ measurement by the Belle collaboration.