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arXiv · 2307.04579

Search for $K^+$ decays into the $\pi^+e^+e^-e^+e^-$ final state

NA62 collaboration
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Abstract

The first search for ultra-rare $K^+$ decays into the $\pi^+e^+e^-e^+e^-$ final state is reported, using a dataset collected by the NA62 experiment at CERN in 2017-2018. An upper limit of $1.4\times 10^{-8}$ at 90% CL is obtained for the branching ratio of the $K^+\to\pi^+e^+e^-e^+e^-$ decay, predicted in the Standard Model to be $(7.2\pm0.7)\times 10^{-11}$. Upper limits at 90% CL are obtained at the level of $10^{-9}$ for the branching ratios of two prompt decay chains involving pair-production of hidden-sector mediators: $K^+\to\pi^+aa$, $a\to e^+e^-$ and $K^+\to\pi^+S$, $S\to A^\prime A^\prime$, $A^\prime\to e^+e^-$.

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NA62 collaboration. 2023-07-10. Search for $K^+$ decays into the $\pi^+e^+e^-e^+e^-$ final state. https://arxiv.org/abs/2307.04579

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