Search for the Higgs boson decays $H\to ee$ and $H\to e\mu$ in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Searches for the Higgs boson decays $H\to ee$ and $H\to e\mu$ are performed using data corresponding to an integrated luminosity of 139 fb${}^{-1}$ collected with the ATLAS detector in $pp$ collisions at $\sqrt{s}=13$ TeV at the LHC. No significant signals are observed, in agreement with the Standard Model expectation. For a Higgs boson mass of 125 GeV, the observed (expected) upper limit at the 95% confidence level on the branching fraction $\mathcal{B}(H\to ee)$ is $3.6\times {10}^{-4}$ ($3.5\times {10}^{-4}$) and on $\mathcal{B}(H\to e\mu )$ is $6.1\times {10}^{-5}$ ($5.8\times {10}^{-5}$). These results represent improvements by factors of about five and six on the previous best limits on $\mathcal{B}(H\to ee)$ and $\mathcal{B}(H\to e\mu )$ respectively.