Global fit to b → cτν transitions

Abstract

Abstract We perform a general model-independent analysis of b → cτ ν ¯ τ $$ b\to c\tau {\overline{\nu}}_{\tau } $$ transitions, including measurements of ℛ D , ℛ D∗, their q 2 differential distributions, the recently measured longitudinal D* polarization F L D ∗ $$ {F}_L^{D\ast } $$ , and constraints from the B c → τ ν ¯ τ $$ {B}_c\to \tau {\overline{\nu}}_{\tau } $$ 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 → cτ ν ¯ τ $$ b\to c\tau {\overline{\nu}}_{\tau } $$ observables, such as the baryonic transition Λ b → Λ c τ ν ¯ τ $$ {\Lambda}_b\to {\Lambda}_c\tau {\overline{\nu}}_{\tau } $$ , the ratio ℛ J/ψ , the forward-backward asymmetries A FB D ∗ $$ {\mathcal{A}}_{\mathrm{FB}}^{D\left(\ast \right)} $$ , the τ polarization asymmetries P τ D ∗ $$ {\mathcal{P}}_{\tau}^{D\left(\ast \right)} $$ , and the longitudinal D* polarization fraction F L D ∗ $$ {F}_L^{D\ast } $$ . 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 ℛ D ∗ $$ {\mathrm{\mathcal{R}}}_{\mathcal{D}\left(\ast \right)} $$ measurement by the Belle collaboration.

Keywords

• Beyond Standard Model
• Effective Field Theories