Publication at Faculty of Mathematics and Physics |
2023
Abstract
The first search for ultra-rare K+decays into the π+e+e-e+e-final state is reported, using a dataset collected by the NA62 experiment at CERN in 2017-2018. An upper limit of 1.4x10-8at 90% CL is obtained for the branching ratio of the K+RIGHTWARDS ARROWπ+e+e-e+e-decay, predicted in the Standard Model to be (7.2 +-0.7) x10-11.
Upper limits at 90% CL are obtained at the level of 10-9for the branching ratios of two prompt decay chains involving pair-production of hidden-sector mediators: K+RIGHTWARDS ARROWπ+aa, a RIGHTWARDS ARROWe+e-and K+RIGHTWARDS ARROWπ+S, SRIGHTWARDS ARROWAA, ARIGHTWARDS ARROWe+e-.