First thought on a high-intensity $K_S$ experiment

The $K \rightarrow \mu\mu$ decays have recently been identified as another golden kaon physics mode alongside the rare $K \rightarrow\pi\nu\bar{\nu}$ processes. These golden modes provide precision tests of the Standard Model with very high sensitivity to New Physics. The presented study is exploring the possibility to address the $K_L - K_S \rightarrow \mu^+\mu^-$ interference experimentally and outlines the challenges associated with such an ambitious project for the far future. A next-generation experiment at the intensity frontier is required that should be capable of collecting a large sample of $\mathcal{O}(10^{14} - 10^{15})$ $K_L$ and $K_S$ decays. Challenges related to the beamline design and detector technology need to be overcome if we want to address this mode experimentally. A significant background suppression of $K_S \rightarrow \pi^+\pi^-$ and radiative $K_L \rightarrow \mu^+\mu^-\gamma$ decays is imperative for a few $\%$ measurement, which would require excellent kinematic resolution and efficient photon detection. The first attempt at a possible experimental setup to measure this effect is presented. Last but not least, a huge number of neutral particles produced offers the possibility to study a plethora of other rare $K_L$, $K_S$ decays as well as hyperon decays enhancing the physics motivation for such an initiative.