Prospects for an experiment to measure BR($K_L\to\pi^0\nu\bar{\nu}$) at the CERN SPS

Understand

Precise measurements of the branching ratios for the $K\to\pi\nu\bar{\nu}$ decays can provide unique constraints on CKM unitarity and, potentially, evidence for new physics.

• It is important to measure both decay modes, $K^+\to\pi^+\nu\bar{\nu}$ and $K_L\to\pi^0\nu\bar{\nu}$, since different new physics models affect the rates for each channel differently.
• We are investigating the feasibility of performing a measurement of BR($K_L\to\pi^0\nu\bar{\nu}$) using a high-energy secondary neutral beam at the CERN SPS in a successor experiment to NA62.
• The planned experiment would reuse some of the NA62 infrastructure, including possibly the NA48 liquid-krypton calorimeter.