Abstract
A
bstract
A search is conducted in proton–proton collisions at the Large Hadron Collider for photon-induced production
pp
→
pp
+
γγ,
(
γγ
→
VX
) of a visible particle
V
decaying into a pair of same-flavour charged leptons (
e
+
e
−
or
μ
+
μ
−
) and an undetected invisible component
X
. Measurements of the outgoing proton energies by the ATLAS forward proton spectrometer allow the full photon–photon four-momentum to be reconstructed. By subtracting the visible four-momentum of the central system measured with the ATLAS detector, the “missing mass” of any event components not detected in the central region can be reconstructed, enabling the reconstruction of
X
without knowing its properties, thus allowing the search to be model-independent. A search for a narrow resonance is performed in the missing-mass spectrum between 100 GeV and 900 GeV. The analysis uses data collected in 2017 from proton–proton collisions at a centre-of-mass energy of
$$ \sqrt{s}=13 $$
s
=
13
TeV, corresponding to an integrated luminosity of 14.7 fb
−
1
. No significant excess over the Standard Model expectation is observed and upper limits at 95% confidence level are set on the fiducial cross sections for three different signal models in the range between 128 and 2.5 fb. Additionally, model-independent limits are set on the visible cross section of BSM processes, for two sets of selection criteria. Both individual lepton flavour decay channels of the visible boson and a combination of the two channels are considered.