Abstract
A
bstract
The electroweak production of
Z
ν
ν
¯
γ
in association with two jets is studied in a regime with a photon of high transverse momentum above 150 GeV using proton–proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider. The analysis uses a data sample with an integrated luminosity of 139 fb
−
1
collected by the ATLAS detector during the 2015–2018 LHC data-taking period. This process is an important probe of the electroweak symmetry breaking mechanism in the Standard Model and is sensitive to quartic gauge boson couplings via vector-boson scattering. The fiducial
Z
ν
ν
¯
γjj
cross section for electroweak production is measured to be
0.77
−
0.30
+
0.34
fb and is consistent with the Standard Model prediction. Evidence of electroweak
Z
ν
ν
¯
γjj
production is found with an observed significance of 3.2
σ
for the background-only hypothesis, compared with an expected significance of 3.7
σ
. The combination of this result with the previously published ATLAS observation of electroweak
Z
ν
ν
¯
γjj
production yields an observed (expected) signal significance of 6.3
σ
(6.6
σ
). Limits on anomalous quartic gauge boson couplings are obtained in the framework of effective field theory with dimension-8 operators.
