$\bar B \to D^{(*)} \ell \bar{X}$ decays in effective field theory with massive right-handed neutrinos

TL;DR

This paper analyzes how massive right-handed neutrinos affect B meson decay distributions within an effective field theory framework, revealing potential distortions in angular observables and implications for experimental anomalies.

Contribution

It provides the first complete differential decay distribution calculations for B decays involving massive right-handed neutrinos in the effective field theory context.

Findings

Massive RH neutrinos cause significant distortions in angular observables.

Massive RH neutrinos are necessary to explain certain experimental asymmetry differences.

Predictions are made for future measurements of angular observables.

Abstract

We calculate the complete differential decay distributions for the $B$ meson decays, $\bar B \to D^{(*)} \ell \bar{X}$, to a massive right-handed (RH) neutrino in the low-energy effective field theory (LEFT) framework. We find that a massive RH neutrino does not introduce any new angular structures compared to the massless case, but can cause significant distortions in angular observables. We study the phenomenology of low-energy four-fermion operators permitted by the standard model effective field theory (SMEFT) extended with RH neutrinos (SMNEFT). We show that to explain the positive value of the difference in forward-backward asymmetries, $\Delta A_{\text{FB}}\equiv A_{\text{FB}}^\mu-A_{\text{FB}}^e$, tentatively inferred from Belle data, the RH neutrino must be massive. We also make predictions for $q^2$ dependent angular observables to motivate future measurements.