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Evidence for light-by-light scattering in ultraperipheral PbPb collisions at √s_(NN) = 5.02 TeV

d’Enterria, David and Anderson, D. and Bornheim, A. and Lawhorn, J. M. and Newman, H. B. and Nguyen, T. Q. and Spiropulu, M. and Vlimant, J. R. and Wilkinson, R. and Xie, S. and Zhang, Z. and Zhu, R. Y. (2019) Evidence for light-by-light scattering in ultraperipheral PbPb collisions at √s_(NN) = 5.02 TeV. Nuclear Physics A, 982 . pp. 791-794. ISSN 0375-9474. doi:10.1016/j.nuclphysa.2018.10.018.

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Evidence for light-by-light (LbL) scattering, γγ→γγ, in ultraperipheral PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV is reported. LbL scattering processes are selected in events with just two photons produced, with transverse energy E_T^γ > 2 GeV, pseudorapidity |η^γ| < 2.4; and diphoton invariant mass m^(γγ) > 5 GeV, transverse momentum p_T^(γγ) < 1 GeV, and acoplanarity (1−Δϕ^(γγ)/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, σ_(fid)(γγ→γγ) = 122±46(stat)±29(syst)±4(theo) nb is consistent with the standard model prediction.

Item Type:Article
Related URLs:
URLURL TypeDescription
Bornheim, A.0000-0002-0128-0871
Lawhorn, J. M.0000-0002-8597-9259
Newman, H. B.0000-0003-0964-1480
Nguyen, T. Q.0000-0003-3954-5131
Spiropulu, M.0000-0001-8172-7081
Xie, S.0000-0003-2509-5731
Zhang, Z.0000-0002-1630-0986
Zhu, R. Y.0000-0003-3091-7461
Additional Information:© 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( Available online 22 January 2019.
Subject Keywords:Light-by-light scattering; Heavy ions; Ultraperipheral collisions; CMS; LHC
Record Number:CaltechAUTHORS:20190228-103740587
Persistent URL:
Official Citation:David d'Enterria, Evidence for light-by-light scattering in ultraperipheral PbPb collisions at sNN=5.02TeV, Nuclear Physics A, Volume 982, 2019, Pages 791-794, ISSN 0375-9474, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:93336
Deposited By: Tony Diaz
Deposited On:28 Feb 2019 18:49
Last Modified:16 Nov 2021 16:57

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