Evidence for light-by-light scattering in ultraperipheral PbPb collisions at √sNN = 5.02 TeV
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| &...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English English English |
| Published: |
Elsevier B.V.
2019
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| Subjects: | |
| Online Access: | http://irep.iium.edu.my/71952/ http://irep.iium.edu.my/71952/ http://irep.iium.edu.my/71952/ 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 |
| Summary: | 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 |
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