Abstract
The NA48/2 experiment at CERN has collected large samples of charged kaons decaying into a pion and two muons for the search of heavy nuetrinos. In addition, its successor NA62 has set new limits on the rate of charged kaon decay into a heavy neutral lepton (HNL) and a lepton, with l = e; μ, using the data collected in 2007 and 2015. New limits on heavy neutrinos from kaon decays into pions, muons and positrons are presented in this report.
Highlights
Two different strategies can in principle be used in heavy neutral lepton (HNL) searches, depending on the assumption made on HNL properties, such as mass and lifetime
In order to improve the detection of the kaon decays the four drift chambers were replaced by a magnetic spectrometer of four chambers with STRAW tubes placed in a vacuum
Events with additional particle were rejected. In both analysis the production of HNL was studied searching for peak in the missing mass spectrum: m2miss. = (PK − P )2, where P represents the 4-momentum of the track reconstructed by the spectrometer under the mass hypothesis of, and PK is the kaon momentum evaluated as the average of the momenta of the 3π system in K+ → π+π+π− decays
Summary
EPJ Web of Conferences new parameters in the Lagrangian explain the open questions about the existence of Dark Matter and the baryon asymmetry of the universe consistent with the observation of neutrino oscillation. The lightest among the three massive neutrinos, with mass of O(10 keV/c2), is considered a dark matter candidate while the other two, with masses of O(100 MeV/c2) give masses to the SM neutrinos via the see-saw mechanism and introduce extra CP violating phases to explain the baryon asymmetry. Since the HNL masses are chosen to be at or below the scale of the electroweak interaction one of the most promising sectors to study HNLs are kaon decays. Large samples of kaon decays have been collected during the last 20 years by the fixed-target experiments NA48 and NA62, located at the Super Proton Synchrotron (SPS) at CERN. This report presents three different searches for HNLs using data collected by the NA48/2 experiment in 2003–2004 and by the NA62 experiment in 2007 and 2015
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