Grant: Subatomic Physics Envelope - Project

High precision measurement of the ultra-rare kaon decay K + to pi + neutrino anti-neutrino (KPNN) at the CERN NA62 experiment will be one of the most incisive probes of quark flavor physics. The branching ratio is sensitive to many new physics models not accessible by other reactions which extend the Standard Model (SM) to solve its considerable problems. The SM prediction for the KPNN branching fraction is broadly recognized to be theoretically robust at the 5% level. Only a precious few accessible loop-dominated quark processes can be predicted with this level of certainty. The suppression of the KPNN branching fraction in the SM to the level 10 -10 allows physics beyond the SM to contribute dramatically to the branching fraction with enhancements of up to factors of five above SM predictions. The certainty with which the SM contribution to KPNN can be predicted will permit a significant discovery potential for new physics with sensitivity unique in quark flavor physics and it allows probing of most models of new physics that couple to quarks within the reach of the LHC. Furthermore, a high precision measurement of KPNN is sensitive to many models of new physics with mass scales well beyond the direct reach of the LHC. NA62 expects to have sensitivity for observing 100 events at the SM level for KPNN covering most of the parameter space for new physics models to contribute. It will also study many other rare or forbidden reactions to search for dark matter, heavy sterile neutrinos, neutral pion decays, and radiative processes.