Missing-mass search in forward-proton-tagged dilepton events with the ATLAS detector

Abstract

A search is conducted in proton-proton collisions at the Large Hadron Collider for photon-induced production $pp\to pp+\gamma \gamma ,(\gamma \gamma \to VX)$ of a visible particle $V$ decaying into a pair of same-flavour charged leptons ($e^{+}{e}^{-}$ or ${\mu }^{+}{\mu }^{-}$) 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 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.

52 pages in total, author list starting page 35, 16 figures, 5 tables, published as JHEP 07 (2026) 236. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2023-13

References in corpus (10)

• The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations
• An Introduction to PYTHIA 8.2
• A new approach to modelling elastic and inelastic photon-initiated production at the LHC: SuperChic 4
• The ALFA Roman Pot Detectors of ATLAS
• Exploration at the high-energy frontier: ATLAS Run~2 searches investigating the exotic jungle beyond the Standard Model
• The quest to discover supersymmetry at the ATLAS experiment
• Elastic photon-initiated production at the LHC: the role of hadron-hadron interactions
• Beam tests of an integrated prototype of the ATLAS Forward Proton detector
• Composite dark matter phenomenology in the presence of lighter degrees of freedom
• Module production of the one-arm AFP 3D pixel tracker