New physics sensitivity in $\Lambda_b\to \Lambda^{(*)}\mu^{+}\mu^{-}$ and $\Lambda_b\to \Lambda^{(*)}\nu\bar{\nu}$ baryonic decays

Abstract

The flavor changing neutral b decays with di-leptons and di-neutrinos in the final state provide a great platform to explore physics beyond the standard model (SM). The recent measurements predicted by LHCb on $R_K$, $R_{K_S}$, $R_{K*+}$, $\mathcal{B}(B_s\to \phi \mu^{+}\mu^{-})$ and $\mathcal{B}(B_s\to \mu^{+}\mu^{-})$ proceeding via $b \to s \ell^{+}\ell^{-}$ quark level transitions show a significant deviation from the standard model expectations. Very recently, Belle II collaboration reported a more precise upper bound of the branching fraction of $\mathcal{B}(B\to K^+\nu\bar{\nu}) < 4.1\times 10^{-5}$ by employing a new inclusive tagging approach. The $b\to s \ell^{+}\ell^{-}$ and $b\to s\nu\bar{\nu}$ decay channels are related in the SM as well as in beyond the SM physics. In the beyond SM physics, they are related via $SU(2)_L$ gauge symmetry and can be studied simultaneously in a model independent standard model effective field theory (SMEFT) approach. Moreover, $b\to s\nu\bar{\nu}$ decay channels are theoretically cleaner than the corresponding $b \to s \ell^{+}\ell^{-}$ decays due to the absence of non factorizable corrections and photonic penguin contributions. In this context, we perform a combined analysis of $\Lambda_b\to \Lambda^{(*)}\mu^{+}\mu^{-}$ and $\Lambda_b\to \Lambda^{(*)} \nu\bar{\nu}$ decay modes and study the implication of $b \to s \ell^{+}\ell^{-}$ anomalies in a model independent SMEFT approach. We give predictions of several physical observables within SM and within several new physics scenarios.