Search for a new Z′ gauge boson in 4μ events with the ATLAS experiment

Abstract

<p>This paper presents a search for a new Z0 vector gauge boson with the ATLAS experiment at the Large Hadron Collider using pp collision data collected at √s = 13TeV, corresponding to an integrated luminosity of 139 fb−1. The new gauge boson Z0 is predicted by Lμ − L models to address observed phenomena that can not be explained by the Standard Model. The search examines the four-muon (4μ) final state, using a deep learning neural network classifier to separate the Z0 signal from the Standard Model background events. The di-muon invariant masses in the 4μ events are used to extract the Z0 resonance signature. No significant excess of events is observed over the predicted background. Upper limits at a 95% confidence level on the Z0 production cross-section times the decay branching fraction of pp ! Z0μμ ! 4μ are set from 0.31 to 4.3 fb for the Z0 mass ranging from 5 to 81 GeV. The corresponding common coupling strengths, gZ0 , of the Z0 boson to the second and third generation leptons above 0.003 – 0.2 have been excluded.<br></p>