# A search for an unexpected asymmetry in the production of $e^+ μ^-$ and $e^- μ^+$ pairs in proton-proton collisions recorded by the ATLAS detector at $\sqrt s = 13$ TeV

ATLAS Collaboration, Paul Newman

Research output: Contribution to journalArticlepeer-review

## Abstract

This search, a type not previously performed at ATLAS, uses a comparison of the production cross sections for $e^+ \mu^-$ and $e^- \mu^+$ pairs to constrain physics processes beyond the Standard Model. It uses $139 \text{fb}^{-1}$ of proton$-$proton collision data recorded at $\sqrt{s} = 13$ TeV at the LHC. Targeting sources of new physics which prefer final states containing $e^{+}\mu^{-}$ to $e^{-}\mu^{+}$, the search contains two broad signal regions which are used to provide model-independent constraints on the ratio of cross sections at the 2% level. The search also has two special selections targeting supersymmetric models and leptoquark signatures. Observations using one of these selections are able to exclude, at 95% confidence level, singly produced smuons with masses up to 640 GeV in a model in which the only other light sparticle is a neutralino when the $R$-parity-violating coupling $\lambda'_{231}$ is close to unity. Observations using the other selection exclude scalar leptoquarks with masses below 1880 GeV when $g_{\text{1R}}^{eu}=g_{\text{1R}}^{\mu c}=1$, at 95% confidence level. The limit on the coupling reduces to $g_{\text{1R}}^{eu}=g_{\text{1R}}^{\mu c}=0.46$ for a mass of 1420 GeV.
Original language English Physics Letters B https://doi.org/10.1016/j.physletb.2022.137106 Accepted/In press - 11 Apr 2022

### Bibliographical note

46 pages in total, author list starting page 30, 14 figures, 6 tables, submitted to Physics Letters B. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2018-29/

• hep-ex

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