Searches for lepton number violation and resonances in $K^{\pm} \to \pi\mu\mu$ decays at NA48/2

The NA48/2 experiment at CERN collected in 2003-2004 a large sample of charged kaon decays with multiple charged particles in the final state. A new upper limit on the rate of the lepton number violating decay obtained from this sample is reported. Moreover searches for two-body resonances in the K (±) → πμμ, decays (including heavy neutral leptons and inflatons) in the accessible range of masses and lifetimes are presented. During the 2016 run the NA62 experiment has collected data with a dedicated trigger for kaon decays with two muons in the final state. Preliminary results on the statistics collected during a period of two weeks for the decay K (+) → π(+)μ(+)μ(−) will be presented. The NA62 experiment has good potential for the studies of rare K (+) decays in addition to its main goal, the measurement of the branching ratio of the decay .