Interpreting the results on exclusive $c\rightarrow s\mu\nu$ modes

TL;DR

This paper analyzes recent BESIII measurements of $D o K\, ext{mu} u$ decay distributions, exploring potential New Physics explanations and their compatibility with LHC constraints, highlighting the limited observability of such effects.

Contribution

It identifies plausible New Physics scenarios compatible with both low-energy and high-energy constraints, and assesses their potential observability in specific decay modes.

Findings

BESIII data shows a mild deviation from Standard Model predictions.

Turning on complex-valued New Physics couplings conflicts with LHC bounds.

Certain scenarios allow compatibility but predict small observable effects.

Abstract

We examine the $q^2$-binned distributions of the $D\to K\mu\nu$ decay rate and of the corresponding forward-backward asymmetry which were recently measured by BESIII, showing a mild deviation from the Standard Model predictions. We point out that the proposed solution to remedy the discrepancy by turning on a complex-valued New Physics coupling is in tension with the constraints deduced from the LHC bounds on the high-$p_T$ tail of the relevant Drell-Yan process. We then show that there are several plausible scenarios that are compatible with both the measured low-energy and high-energy constraints but the selected couplings appear to be too small to be observed in the measurements of integrated observables, except for possibly the $q^2$-binned distribution of the angular observables relevant to $D_s\to \phi (\to KK) \mu\nu$ or $\Lambda_c\to \Lambda (\to p \pi) \mu\nu$ modes.