Searches for Lepton Number Violation and Resonances in $K^{\pm }\to \pi \mu \mu$ Decays

Abstract

The NA48/2 experiment at CERN collected a large sample of charged kaon decays to final states with multiple charged particles in 2003--2004. A new upper limit on the rate of the lepton number violating decay $K^{\pm }\to {\pi }^{\mp }{\mu }^{\pm }{\mu }^{\pm }$ is reported: $\mathcal{B}(K^{\pm }\to {\pi }^{\mp }{\mu }^{\pm }{\mu }^{\pm })<8.6\times 10^{-11}$ at 90% CL. Searches for two-body resonances $X$ in $K^{\pm }\to \pi \mu \mu$ decays (such as heavy neutral leptons $N_4$ and inflatons $\chi$) are also presented. In the absence of signals, upper limits are set on the products of branching fractions $\mathcal{B}(K^{\pm }\to {\mu }^{\pm }{N}_4)\mathcal{B}(N_4\to \pi \mu )$ and $\mathcal{B}(K^{\pm }\to {\pi }^{\pm }X)\mathcal{B}(X\to {\mu }^{+}{\mu }^{-})$ for ranges of assumed resonance masses and lifetimes. The limits are in the $(10^{-11},10^{-9})$ range for resonance lifetimes below 100 ps.

arXiv comment15 pages, accepted for publication in Physics Letters B

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