Search for resonant leptoquark production via lepton-jet signatures in $pp$ collisions at $\sqrt{s}=13$ TeV and $\sqrt{s}=13.6$ TeV with the ATLAS detector

Abstract

This paper presents a search for physics beyond the Standard Model targeting a heavy resonance visible in the invariant mass of the lepton-jet system. The analysis focuses on final states with a high-energy lepton and jet, and is optimised for the resonant production of leptoquarks-a novel production mode mediated by the lepton content of the proton originating from quantum fluctuations. Four distinct and orthogonal final states are considered: $e$+light jet, $\mu$+light jet, $e$+$b$-jet, and $\mu$+$b$-jet, constituting the first search at the Large Hadron Collider for resonantly produced leptoquarks with couplings to electrons and muons. Events with an additional same-flavour lepton, as expected from higher-order diagrams in the signal process, are also included in each channel. The search uses proton-proton collision data from the full Run 2, corresponding to an integrated luminosity of 140 fb${}^{-1}$ at a centre-of-mass energy of $\sqrt{s}=13$ TeV, and from a part of Run 3 (2022-2023), corresponding to 55 fb${}^{-1}$ at $\sqrt{s}=13.6$ TeV. No significant excess over Standard Model predictions is observed. The results are interpreted as exclusion limits on scalar leptoquark (${\tilde{S}}_1$) production, substantially improving upon previous ATLAS constraints from leptoquark pair production for large coupling values. The excluded ${\tilde{S}}_1$ mass ranges depend on the coupling strength, reaching up to 3.4 TeV for quark-lepton couplings $y_{de}=1.0$, and up to 4.3 TeV, 3.1 TeV, and 2.8 TeV for $y_{s\mu }$, $y_{be}$, and $y_{b\mu }$ couplings set to 3.5, respectively.

60 pages in total, author list starting page 43, 17 figures, 8 tables, published in JHEP. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2024-12/

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