Study for an experiment to measure the KL → π0νν¯ decay at CERN

The K → πνν decays are flavour-changing neutral current (FCNC) processes, very suppressed in the Standard Model (SM). The latter, moreover, predicts their branching ratios (BR) with high precision, making them excellent probes of new physics. The NA62 experiment at the CERN Super Proton Synchrotron (SPS), currently taking data, is measuring the BR of the K+ → π+νν¯ decay. The KOTO experiment at JPARC, using a low-energy KL beam, foresees to reach the SM sensitivity for KL → π0νν¯ by 2021. A complementary measurement of KL → π0νν¯ exploiting part of the NA62 existing apparatus could be possible at the SPS with a high-energy KL beam. Ongoing studies indicate the possibility of observing 60 decay events in 5 years of data taking with a signal-to-background ratio of 1