Search for Lepton Number and Lepton Flavour Violation proces ses at the NA62 experiment at CERN

The research is focused on two aspects of the NA62 experiment at CERN.
The first goal is the development of the design of the optical system for a future differential Cherenkov detector to be installed in the NA62 high-intensity hadron beam. The future detector is different from the current one in that it uses hydrogen radiator gas rather than nitrogen, which makes the detector thinner by a factor of about three and reduces multiple scattering of beam particles and therefore the associated background. The second goal is the search for the production of the massless dark photon (A') in the decay K+ --> pi+ pi0 A' using the large data set collected by the NA62 experiment using a downscaled control trigger in 2016-2018, which is a part of the NA62 hidden sector search programme.