Searches for lepton number violating K+ -> pi(-)e(+)e(+) and K+ -> pi(-)pi(0)e(+)e(+) decays have been performed using the complete dataset collected by the NA62 experiment at CERN in 2016-2018. Upper limits of 5.3 x 10(-11 )and 8.5 x 10(-10) are obtained on the decay branching fractions at 90% confidence level.
The former result improves by a factor of four over the previous best limit, while the latter result represents the first limit on the K+ -> pi(-)pi(0)e(+)e(+) decay rate. (C) 2022 The Author. Published by Elsevier B.V.