Disentangling left and right-handed neutrino effects in $B\rightarrow K^{(*)}\nu\nu$

TL;DR

This paper analyzes the Belle II measurement of $B^+ ightarrow K^+ u u$ within the SMEFT framework extended by a light right-handed neutrino, exploring how various observables can distinguish neutrino chiralities and using LHC data to constrain models.

Contribution

It introduces a comprehensive analysis of left- and right-handed neutrino effects in $B$ decays, combining flavor observables with collider constraints to identify viable new physics scenarios.

Findings

Belle II result is nearly 3σ above Standard Model expectations.

Correlations between decay modes can differentiate neutrino chiralities.

LHC Drell-Yan data constrains right-handed neutrino scenarios.

Abstract

The first observation of $\mathcal{B}\left(B^+\rightarrow K^+\nu\nu\right)$ by the Belle II experiment lies almost $3\sigma$ away from the Standard Model expectation. In this letter we study this result in the SMEFT, extended by a light right-handed neutrino. We explore the correlations between the measured decay rate and other observables, such as $\mathcal{B}\left(B\rightarrow K^*\nu\nu\right)$ and $F_L\left(B\rightarrow K^*\nu\nu\right)$, showing that they could disentangle among scenarios involving left-handed neutrinos and those with the right-handed ones. Furthermore, we find that the high-$p_T$ tails of Drell-Yan processes studied at LHC provide important constraints that help us exclude some of the scenarios consistent with the Belle II result.