# Searches for lepton number violating $K^+$ decays

## TL;DR

The NA62 experiment searched for lepton number violating $K^+$ decays, setting new upper limits on their branching fractions, which improves previous constraints and contributes to understanding rare kaon decays.

## Contribution

This work provides the first search for these specific lepton number violating decays using 2017 data, setting more stringent upper limits than prior measurements.

## Key findings

- No signals observed for the decays.
- Upper limits on branching fractions: $2.2\times 10^{-10}$ and $4.2\times 10^{-11}$.
- Limits improve previous results by factors of 3 and 2.

## Abstract

The NA62 experiment at CERN reports a search for the lepton number violating decays $K^+\to\pi^-e^+e^+$ and $K^+\to\pi^-\mu^+\mu^+$ using a data sample collected in 2017. No signals are observed, and upper limits on the branching fractions of these decays of $2.2\times 10^{-10}$ and $4.2\times 10^{-11}$ are obtained, respectively, at 90% confidence level. These upper limits improve on previously reported measurements by factors of 3 and 2, respectively.