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Joined 2026-09-21 Message
Incoming links: Ultra-peripheral collision
The ATLAS experiment used lead ion collisions at the Large Hadron Collider to study the vacuum QED process. In an ultra-peripheral collision, the nuclei pass without an ordinary nuclear collision; their strong electromagnetic fields supply nearly real photons. Selecting two nearly back-to-back photons with little other detector activity isolated the rare channel. The 2017 result used at and found 13 candidates against an expected background of . This was evidence, with a reported significance of standard deviations.[ref]
Evidence for light-by-light scattering in heavy-ion collisions with the ATLAS detector at the LHC by ATLAS Collaboration. Abstract: sample size, collision energy, candidate count, background and fiducial photon selection
[ref]https://atlas.cern/updates/press-statement/atlas-sees-first-direct-evidence-light-light-scattering-high-energy. 14 August 2017 statement: significance and dedicated two-photon trigger with otherwise little detector activity
The ATLAS Collaboration reports the ATLAS evidence for light-by-light scattering in 2017 from ultra-peripheral collisions of lead ions. The paper states the event selection and background estimate; its abstract gives the candidate count and the fiducial scattering cross-section.