Exploratory lattice QCD study of the rare kaon decay $K^+ \to \pi^+ \nu \bar\nu$

Abstract

As flavor changing neutral current processes, rare kaon decays K !pn ¯ n are highly suppressed in the standard model and thus provide ideal probes for the observation of new physics effects. Given the importance of rare kaon decays, the CERN NA62 experiment aims at an observation of O(100) events of K+ !p+n ¯ n decay and a 10%-precision measurement of the branching ratio in two years. Another experiment, J-PARC KOTO, is dedicated to search for the CP-violating KL ! p0n ¯ n decay. Recognizing that the standard model predictions will soon be confronted with new experimental results, it is important to determine the long-distance contributions to K+ !p+n ¯ n with a controlled error. Here I will present an exploratory calculation of the longdistance contributions to the K+ ! p+n ¯ n decay amplitude from first principles using lattice QCD.