CP violation in B ¯ 0 → D ∗ + μ − ν ¯ μ $$ {\overline{B}}^0\to {D}^{\ast +}{\mu}^{-}{\overline{\nu}}_{\mu } $$

Abstract

Abstract In order to explain the observed anomalies in the measurements of R D ∗ $$ {R}_{D^{\left(\ast \right)}} $$ and R J/ψ , a variety of new-physics (NP) models that contribute to b → c τ − ν ¯ $$ b\to c{\tau}^{-}\overline{\nu} $$ have been proposed. In this paper, we show how CP-violating observables can be used to distinguish these NP models. Because p → τ $$ {\overrightarrow{p}}_{\tau } $$ cannot be measured (the decay products of the τ include the undetected ν τ ), obtaining the angular distribution of B ¯ 0 → D ∗ + τ − ν ¯ τ $$ {\overline{B}}^0\to {D}^{\ast +}{\tau}^{-}{\overline{\nu}}_{\tau } $$ is problematic. Instead, we focus here on B ¯ 0 → D ∗ + → D 0 π + μ − ν ¯ μ $$ {\overline{B}}^0\to {D}^{\ast +}\left(\to {D}^0{\pi}^{+}\right){\mu}^{-}{\overline{\nu}}_{\mu } $$ . This process may also receive contributions from the same NP, and LHCb intends to measure the CP-violating angular asymmetries in this decay. There are two classes of NP models that contribute to b → c μ − ν ¯ μ $$ b\to c{\mu}^{-}{\overline{\nu}}_{{}_{\mu }} $$ . These involve (i) a W ′ (two types) or (ii) a leptoquark (LQ) (six types). The most popular NP models predict no CP-violating effects, so the measurement of nonzero CP-violating asymmetries would rule them out. Furthermore these measurements allow one to distinguish the W ′ and LQ models, and to differentiate among several LQ models.

Keywords

• Beyond Standard Model
• CP violation