Rare Kaon Decay to Missing Energy: Implications of the NA62 Result for a $Z^\prime$ Model

Abstract

Meson decays offer a good opportunity to probe new physics. The rare kaon decay K + → π + ν ν is one of the cleanest of them and, for this reason, is rather sensitive to new physics, in particular, vector mediators. NA62 collaboration, running a fixed-target experiment at CERN, recently reported an unprecedented sensitivity to this decay, namely a branching fraction of BR(K + → π + ν ν) = (11 +4.0 −3.5 ) × 10 −11 at 68% C.L. Vector mediators that couple to neutrinos may yield a sizeable contribution to this decay. Motivated by the new measurement, we interpret this result in the context of a concrete Z model, and put our findings into perspective with the correlated KL → π 0 ν ν decay measured by KOTO collaboration, current, and future colliders, namely the High-Luminosity and High-Energy LHC.