Probing Signatures of Right-Handed Neutrinos via $b\to s\nu \bar{\nu }$ Decays

Abstract

The recent Belle II measurement of $\mathcal{B}(B^{+}\to K^{+}\nu \bar{\nu })$, which deviates from the Standard Model prediction, provides a strong motivation to search for New Physics in $b\to s\nu \bar{\nu }$ 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 $\mathcal{B}(B\to K\nu \bar{\nu })$ together with the upper limit on $\mathcal{B}(B\to K^{\ast }\nu \bar{\nu })$, we constrain the new physics interactions. We study the correlation of $\mathcal{B}(B\to K\nu \bar{\nu })$ with $\mathcal{B}(B\to K^{\ast }\nu \bar{\nu })$, $\mathcal{B}(B_s\to \varphi \nu \bar{\nu })$, $\mathcal{B}({\Lambda }_b\to \Lambda \nu \bar{\nu })$, and the longitudinal polarization fraction $F_L^{K^{\ast }}$. We find sizeable enhancements in all branching fractions studied, while $F_L^{K^{\ast }}$ 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.

18 pages, 5 figures, 1 table