Abstract
The NA62 experiment at the CERN SPS provides unique opportunity to study rare and forbidden decays of K + mesons. Using the data collected in 2017 a search for the lepton number violating decays K + → π − µ + µ + and K + → π − e + e + has been performed. New upper limits on the branching ratio have been obtained: 4.2×10−11 for the muon and 2.2×10−10 for the electron mode (90% confidence level). These results improve the existing limits by factors of 2 and 3 respectively.
Highlights
A lot of scenarios beyond the Standard Model (SM) allow for lepton flavor violating (LFV) and lepton number violating (LNV) processes
The beam particle identification is performed by a Cherenkov differential counter (KTAG), while a Ring Imaging Cherenkov (RICH) detector is used for the separation of pions and muons produced in kaon decays, as well as for the precise timing
The event selection starts with the requirement on the presence of a good quality 3-track vertex reconstructed in the fiducial volume: 114 m < Zvtx < 180 m for the muon mode (105 m < Zvtx < 180 m for the electron mode) and the total charge equal to +1 e
Summary
A lot of scenarios beyond the Standard Model (SM) allow for lepton flavor violating (LFV) and lepton number violating (LNV) processes. The best upper limits obtained so far come from the CERN NA48/2 experiment for the muon mode [3] (BR(K+ → π−μ+μ+) < 8.6 × 10−11) and from BNL E865 for the electron mode [4] (BR(K+ → π−e+e+) < 6.4 × 10−10).
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