Observation of light-by-light scattering in ultraperipheral Pb+Pb collisions with the ATLAS detector Aad, G. Aguilar Saavedra, Juan Antonio Atlas Collaboration This letter describes the observation of the light-by-light scattering process, γγ→γγ, in Pb+Pb collisions at sNN−−−√ = 5.02 TeV. The analysis is conducted using a data sample corresponding to an integrated luminosity of 1.73 nb−1, collected in November 2018 by the ATLAS experiment at the LHC. Light-by-light scattering candidates are selected in events with two photons produced exclusively, each with transverse energy EγT>3 GeV and pseudorapidity |ηγ|<2.37, diphoton invariant mass above 6 GeV, and small diphoton transverse momentum and acoplanarity. After applying all selection criteria, 59 candidate events are observed for a background expectation of 12 ± 3 events. The observed excess of events over the expected background has a significance of 8.2 standard deviations. The measured fiducial cross section is 78 ± 13 (stat.) ± 7 (syst.) ± 3 (lumi.) nb. 2020-04-29T11:45:57Z 2020-04-29T11:45:57Z 2019-07-31 info:eu-repo/semantics/article Aad, G. (2019). Observation of Light-by-Light Scattering in Ultraperipheral Pb+ Pb Collisions with the ATLAS Detector. PHYSICAL REVIEW LETTERS Phys Rev Lett, 123, 052001. http://hdl.handle.net/10481/61704 10.1103/PhysRevLett.123.052001 eng http://creativecommons.org/licenses/by/3.0/es/ info:eu-repo/semantics/openAccess Atribución 3.0 España American Physical Society