Searches for new physics with high-intensity kaon beams

Abstract

The availability of high-intensity kaon beams at the J-PARC Hadron Experimental Facility and the CERN SPS North Area, together with the abundant forward production of kaons at the LHC, gives rise to unique possibilities for sensitive tests of the Standard Model in the quark flavor sector. Precise measurements of the branching ratios for the flavor-changing neutral current decays $K\to\pi\nu\bar{\nu}$ can provide unique constraints on CKM unitarity and, potentially, evidence for new physics. Building on the success of the current generation of fixed-target experiments, initiatives are taking shape in both Europe and Japan to measure the branching ratio for $K^+\to\pi^+\nu\bar\nu$ to ~5% and for $K_L\to\pi^0\nu\bar\nu$ to ~20\% precision. These planned experiments would also carry out lepton flavor universality tests, lepton number and flavor conservation tests, and perform other precision measurements in the kaon sector, as well as searches for exotic particles in kaon decays. Meanwhile, the LHCb experiment is ready to restart data taking with a trigger upgrade that will vastly increase its sensitivity for rare $K_S$ decays and complementary hyperon decays. We overview the initiatives for next-generation experiments in kaon physics in Europe and Japan, identifying potential contributions from the US high-energy physics community.