Evidence for light-by-light scattering in ultraperipheral PbPb collisions at √sNN = 5.02 TeV

• Main Authors: D'Enterria, David, Sirunyan, A. M., Tumasyan, A. R., Adam, Wolfgang, Ambrogi, Federico, Md. Ali, Mohd. Adli
• Format: Article
• Language: English; English; English
• Published: Elsevier B.V. 2019
• Subjects: Q Science (General); QC Physics
• Online Access: http://irep.iium.edu.my/71952/1/71952_Evidence%20for%20light-by-light%20scattering_article.pdf; http://irep.iium.edu.my/71952/2/71952_Evidence%20for%20light-by-light%20scattering_wos.pdf; http://irep.iium.edu.my/71952/3/71952_Evidence%20for%20light-by-light%20scattering_scopus.pdf; http://irep.iium.edu.my/71952/; https://reader.elsevier.com/reader/sd/pii/S0375947418302914?token=0A13A963173A3A4ADD05DAA01ACBCEA49094AEDCA32F602BFE1E38CC192E19A0BE190D27AE0C0E742D1E2967CCDAD366

Evidence for light-by-light (LbL) scattering, γγ → γγ, in ultraperipheral PbPb collisions at a nucleon-nucleon centerof-mass energy of 5.02 TeV is reported. LbL scattering processes are selected in events with just two photons produced, with transverse energy Eγ T > 2 GeV, pseudorapidity |ηγ| < 2.4; and diphoton invariant mass mγγ > 5 GeV, transverse momentum pγγ T < 1 GeV, and acoplanarity (1 − Δφγγ/π) < 0.01. After all selection criteria, 14 events are observed, compared to 11.1 ± 1.1 (theo) and 3.8 ± 1.3 (stat) events expected for signal and background processes respectively. The significance of the signal excess over the background-only hypothesis is 4.1σ. The measured fiducial LbL scattering cross section, σfid(γγ → γγ) = 122 ± 46 (stat) ±29 (syst) ±4 (theo) nb is consistent with the standard model prediction