Tension in the inclusive versus exclusive determinations of $|V_{cb}|$: a possible role of new physics

TL;DR

This paper explores whether new physics, specifically a tensor operator with lepton flavor dependence, can explain the discrepancy in |V_{cb}| measurements from inclusive and exclusive B decays, finding parameter regions that reconcile both.

Contribution

It introduces a modified effective Hamiltonian with a tensor operator to account for the |V_{cb}| tension, considering lepton flavor dependence and analyzing its impact on decay modes.

Findings

Identifies parameter regions where new physics explains the |V_{cb}| discrepancy.

Shows the tensor operator's different effects on muon and electron decay channels.

Demonstrates compatibility of new physics with existing decay constraints.

Abstract

We reconsider the possibility that the tension in the $|V_{cb}|$ determinations from inclusive and exclusive $B$ decay modes is due to a new physics effect. We modify the Standard Model effective Hamiltonian for semileptonic $b \to c$ transitions including a tensor operator with a lepton flavour dependent coupling $\epsilon_T^\ell$, and investigate separately the muon and electron modes. The interference term between SM and NP, proportional to the lepton mass, has different impact in the inclusive and exclusive $B$ modes to muon. Moreover, even when the lepton mass is small as for the electron, the NP effect is different in inclusive and exclusive $B$ channels. For both $\mu$ and $e$ we find a region of $\epsilon_T^{\mu,\,e}$ where the constraints from $B^- \to D^{(*)0} \ell^- {\bar \nu}_\ell$ and $B \to X_c \, \ell \, \bar \nu_\ell$ are satisfied for the same $|V_{cb}|$.