Speakers
Description
Precision measurements of the branching ratios (BRs) for rare kaon decays can provide unique constraints on CKM unitarity and may reveal the existence of new physics. Building upon a CERN tradition of groundbreaking experiments in kaon physics, including, most recently, NA62's successful application of the in-flight technique to measure BR($K^+ \to \pi^+\nu\bar{\nu}$), we envision a comprehensive program for the study of the rare decay modes of both $K^+$ and $K_L$ mesons, to be carried out with high-intensity kaon beams from the CERN SPS in multiple phases starting in LHC Run 3 (2026), including both an experiment to measure BR($K^+ \to \pi^+\nu\bar{\nu}$) at the 5% level and an experiment to measure BR($K_L \to\pi^0\nu\bar{\nu}$) at the 20% level. The detectors could also be reconfigured to allow measurements of $K_L$ decays with charged particles, such as $K_L\to\pi^0\ell^+\ell^-$. In addition, the availability of high-intensity proton and kaon beams and detectors with redundant PID systems and precise timing will allow for a wide range of searches for rare phenomena beyond the kaon sector, including dark sector particles produced in kaon and pion decays or in interactions in the experiment’s target or beam dump.
