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

TL;DR

This paper reports a search for a new Z' gauge boson in four-muon events at the LHC using deep learning, setting limits on its production cross-section and coupling strength, with no significant signal found.

Contribution

It introduces a novel search for Z' bosons in the 4μ final state using deep learning classifiers to improve signal-background separation.

Findings

No significant excess observed over background.

Upper limits set on Z' production cross-section from 0.31 to 4.3 fb.

Excluded Z' coupling strengths above 0.003 - 0.2 for masses 5-81 GeV.

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.