New limits on heavy neutrinos from Kaon experiments at CERN

Abstract

The NA48/2 and NA62-$R_K$ experiments at CERN collected large samples of charged kaon decays in 2003--2004 and 2007, respectively. These samples, collected with different trigger conditions, allow to search for both short and long-living heavy neutrinos produced in $K^{\pm }\to {\mu }^{\pm }{N}_4$ decays. The results of these complementary searches are presented in this letter. In the absence of observed signal, the limits obtained on $\mathcal{B}(K^{\pm }\to {\pi }^{\mp }{\mu }^{\pm }{\mu }^{\pm })$, $\mathcal{B}(K^{\pm }\to {\mu }^{\pm }{N}_4)\mathcal{B}(N_4\to \pi \mu )$, $\mathcal{B}(K^{+}\to {\mu }^{+}{N}_4)$ and on the mixing matrix element $|U_{\mu 4}{|}^2$ are reported.

arXiv comment8 pages, 10 figures. To be published in La Thuile 2017 conference proceedings