Search for $K_{S,L}$ oscillations and invisible decays into the dark sector at NA64

TL;DR

This paper explores the potential to detect rare $K_{S,L}$ decays and oscillations into the dark sector at NA64, considering extensions of the Standard Model that could enhance these decay rates to measurable levels.

Contribution

It proposes experimental searches for $K_{S,L}$ decays and oscillations into the dark sector at NA64, focusing on models that could increase branching ratios.

Findings

Potential sensitivity to $Br(K_{S,L})$ up to $10^{-7}-10^{-5}$

Extensions of the Standard Model can significantly enhance decay probabilities

Experimental feasibility of detecting dark sector oscillations at CERN

Abstract

The decays $K_{S,L}$ have never been experimentally tested. In the Standard Model their branching ratios for the decay into two neutrinos are predicted to be extremely small, $Br(K_{S,L} \to \nu \bar{\nu}) \lesssim 10^{-16}$. We consider several natural extensions of the SM, such as two-Higgs-doublet (2HDM), 2HDM and light scalar, and dark mirror sector models, that allow to enhance the $Br(K_{S,L})$ up to a measurable level. We briefly discuss the possible search for $K_{S,L}$ decays and $K_{S,L}$ oscillations into the dark sector at the NA64 experiment at CERN with the sensitivity to $Br(K_{S,L}) \lesssim 10^{-7}-10^{-5}$.