|Vub| determination and testing of lepton flavour universality in semileptonic Bc → D(∗) decays

Abstract

Abstract In light of prospects for measurements of B c → D (∗) lv decays in the upcoming Upgrade II of the LHC, we show that by using calculated B c → D (∗) form factors a competitive extraction of the |V ub | CKM matrix element from the B c → Dμ v ¯ μ $$ {B}_c\to D\mu {\overline{v}}_{\mu } $$ decay might be possible. To minimize experimental and theoretical uncertainties we provide the ratio |V ub |/|V cb | by normalizing the B c → D ∗ μ v ¯ μ $$ {B}_c\to {D}^{\left(\ast \right)}\mu {\overline{v}}_{\mu } $$ to B c → J / ψμ v ¯ μ $$ {B}_c\to J/\psi \mu {\overline{v}}_{\mu } $$ decay. We also briefly examine the suggestion to extract |V ub |/|V cs | from the theoretically interesting ratio of B c → D 0 e v ¯ e $$ {B}_c\to {D}^0e{\overline{v}}_e $$ and B c → B s e v ¯ e $$ {B}_c\to {B}_se{\overline{v}}_e $$ decay rates in the zero-recoil limit. With the present average value of |V ub |, the predicted branching ratios are estimated to be BR B c → D 0 μ ν ¯ μ = 2.4 ± 0.4 · 10 − 5 $$ BR\left({B}_c\to {D}^0\mu {\overline{\nu}}_{\mu}\right)=\left(2.4\pm 0.4\right)\cdotp {10}^{-5} $$ and BR B c → D ∗ μ ν ¯ μ = 7 ± 3 · 10 − 5 , $$ BR\left({B}_c\to {D}^{\ast}\mu {\overline{\nu}}_{\mu}\right)=\left(7\pm 3\right)\cdotp {10}^{-5}, $$ and the semileptonic ratios for testing the lepton flavour universality in these B c decays are R c (D 0) = 0.64 ± 0.05 and R c (D ∗ ) = 0.55 ± 0.05. We also provide q 2 distributions and various angular observables of B c → D (∗) lν decays.

Keywords

• Heavy Quark Physics
• Nonperturbative Effects