Search for axion-like particle produciton in kaon decays at CERN-NA62 experiment

It is proposed to perform the first search for production of a short-lived axion-like particle (ALP) in charged-kaon decays (K+ --> pi+a), which decaying promptly into a di-photon final state, using world's largest data set of charged kaon decays collected by the NA62 experiment at CERN in 2016-18.

New powerful constraint on the ALP phase space will be established; a possible ALP discovery would be a breakthrough in particle physics.

To achieve credible results on the ALP search, it is mandatory to understand the main Standard Model background process K+ --> pi+ gamma gamma.

Therefore a comprehensive study of this process is also proposed, including a re-analysis of the inputs to the description of this decay within Chiral Perturbation Theory, and the most precise measurement of this process to date. This measurement by itself represents an important test of the theories describing low-energy dynamics.

These novel measurements are based on an existing data sample collected recently, thereby minimizing the associated risks.