Probing Signatures of Right-Handed Neutrinos via $b \to s ν\barν$ Decays

Abstract

The recent Belle II measurement of $\mathcal{B}(B^+\to K^+ν\barν)$, which deviates from the Standard Model prediction, provides a strong motivation to search for New Physics in $b\to sν\barν$ transitions. We perform a model-independent analysis within the low-energy effective theory, focusing on dimension-six vector operators involving right-handed neutrinos. Using the Belle II measurement of $\mathcal{B}({B\to Kν\barν})$ together with the upper limit on $\mathcal{B}({B\to K^{*}ν\barν})$, we constrain the new physics interactions. We study the correlation of $\mathcal{B}({B\to Kν\barν})$ with $\mathcal{B}({B\to K^{*}ν\barν})$, $\mathcal{B}({B_s\toϕν\barν})$, $\mathcal{B}({Λ_b\toΛν\barν})$, and the longitudinal polarization fraction $F_L^{K^*}$. We find sizeable enhancements in all branching fractions studied, while $F_L^{K^*}$ offers complementary sensitivity to the underlying RHN interaction structure. These results provide testable signatures of right-handed neutrino interactions at Belle~II and LHCb, and at the future FCC-ee experiment.