Abstract
A
bstract
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
s
= 13 TeV, corresponding to an integrated luminosity of 139 fb
−
1
. The new gauge boson
Z
′ is predicted by
L
μ
−
L
τ
models to address observed phenomena that can not be explained by the Standard Model. The search examines the four-muon (4
μ
) 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
μ
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 → Z
′
μμ →
4
μ
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.