Search for a new Z' gauge boson in $4\mu$ events with the ATLAS experiment

The ATLAS collaboration
CERN-EP-2022-251, 2023.

Abstract (data abstract)
This paper presents a search for a new $Z'$ vector gauge boson with the ATLAS experiment at the Large Hadron Collider using $pp$ collision data collected at $\sqrt{s} = 13$ TeV, corresponding to an integrated luminosity of 139 fb$^{-1}$.The new gauge boson $Z'$ is predicted by $L_{\mu}-L_{\tau}$ models to address observed phenomena that can not be explained by the Standard Model.The search examines the four-muon (4$\mu$) final state, using a deep learning neural network classifier to separate the $Z'$ signal from the Standard Model background events.The di-muon invariant masses in the $4\mu$ events are used to extract the $Z'$ resonance signature.No significant excess of events is observed over the predicted background.Upper limits at a 95% confidence level on the $Z'$ production cross-section times the decay branching fraction of $pp \rightarrow Z'\mu\mu \rightarrow 4\mu$ are set from 0.31 to 4.3 fb for the $Z'$ mass ranging from 5 to 81 GeV.The corresponding common coupling strengths, $g_{Z'}$, of the $Z'$ boson to the second and third generation leptons above 0.003 -- 0.2 have been excluded.

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