Abstract
Thanks to a large sample of kaon decays collected in 2003-2004, the NA48/2 experiment at CERN is able to set an upper limit on the rate of the lepton number violating decay BR(K±→π∓μ±μ±)< 8.6 × 10-11 at 90%CL, and to set limits at the 10-10 — 10-9 level on the appearance of resonances (including heavy neutral leptons N4 and inflatons χ) in the K±→πμμ decays as functions of the resonance mass and lifetime.
Highlights
The observation of neutrino oscillations is so far the only indication of lepton flavour nonconversation; models of physics beyond the Standard Model (SM) often include more general phenomena of Lepton Flavour Violation (LFV) and Lepton Number Violation (LNV)
In order to select the KLNV ( KLNC ) candidates, a vertex composed of one π± candidate and a pair of identically charged muon candidates is required, with the following additional criteria: for the pion, the ratio of energy E in the liquid Kripton electromagnetic calorimeter (LKr) calorimeter to momentum p measured in the spectrometer is E/p < 0.95 to suppress electrons; the pion has no in-time associated hits in the muon detector; the muon candidates have E/p < 0.2 and associated hits in the first two planes of the muon detector; the pion candidate is required to have momentum above 15 GeV/c to ensure high muon rejection efficiency
One event is observed in the signal mass region after applying the KLNV selection, while 3489 candidates are selected with the KLNC selection
Summary
The observation of neutrino oscillations is so far the only indication of lepton flavour nonconversation; models of physics beyond the Standard Model (SM) often include more general phenomena of Lepton Flavour Violation (LFV) and Lepton Number Violation (LNV).
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