$\Lambda_b\to\Lambda^{(*)}\nu{\bar\nu}$ and $b\to s$ $B$ decays

Abstract

The baryonic $b\to s$ transition $\Lambda_b\to\Lambda^{(*)}\nu{\bar\nu}$ is analyzed. We combine the mesonic counterpart $B^+\to K^+\nu{\bar\nu}$ and $B^0\to K^{*0}\nu{\bar\nu}$ as well as other observables involving $B$ mesons like $R(K^{(*)})$, ${\rm Br}(B_s\to\mu^+\mu^-)$, ${\rm Br}(B^+\to K^+\mu^+\mu^-)$, and $P_5'(B^+\to K^{*+}\mu^+\mu^-)$. Using the constraints from mesonic sector, we present predictions for the currently unobserved baryonic decay modes, which is very complementary to mesonic modes for probing new physics. We find that the new physics scale $M_{\rm NP}$ to be $2.04~{\rm TeV}\le M_{\rm NP} \le 11.76~{\rm TeV}$ (at $1\sigma$) for ordinary heavy new mediators. Our predictions for the branching ratios ${\rm Br}(\Lambda_b\to\Lambda^{(*)}\nu{\bar\nu})$ are $2.07 (1.07)$ times the standard model estimations, which could be verified at future colliders. We also find a sum rule for ${\rm Br}(\Lambda_b\to\Lambda \nu{\bar\nu})$ and ${\rm Br}(B\to K^{(*)}\nu{\bar\nu})$ that is very similar to that for $b\to c$ semi-leptonic decays.