Are the new particles heavy or light in \(b \rightarrow s E_{\textrm{miss}}\)?

In this work, we study the \(B^+\rightarrow K^+ E_{\textrm{miss}}\), \(B^0\rightarrow K^{*0} E_{\textrm{miss}}\), and \(\Lambda _b^0\rightarrow \Lambda ^0 E_{\textrm{miss}}\) decays under three different new physics hypotheses: the heavy new particles, the light neutral vector particles, and the axion-like particles. We find that all three hypotheses can resolve the Belle-II excess, and they can be clearly distinguished by the longitudinal polarization fraction of \(K^*\). Furthermore, we discover that the longitudinal polarization fraction of \(\Lambda \) can be used to distinguish the chirality of the effective operators.