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

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 $pp\to Z^{\prime }\mu \mu \to 4\mu$ are set from 0.31 to 4.3 fb for the Z' mass ranging from 5 to 81 GeV. The corresponding common coupling strengths, $g_{Z^{\prime }}$, of the Z' boson to the second and third generation leptons above 0.003 - 0.2 have been excluded.

45 pages in total, author list starting at page 26, 7 figures, 3 tables, published by JHEP. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HDBS-2018-57/

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• Probing a low-mass $Z^{\prime }$ gauge boson at IceCube and prospects for IceCube-Gen2
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