Evidence for light-by-light scattering in heavy-ion collisions with the ATLAS detector at the LHC
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Light-by-light scattering (γγ right arrow γγ) is a quantum-mechanical process that is forbidden in the classical theory of electrodynamics. This reaction is accessible at the Large Hadron Collider thanks to the large electromagnetic field strengths generated by ultra-relativistic colliding lead ions. Using 480 μb−1 of lead–lead collision data recorded at a centre-of-mass energy per nucleon pair of 5.02 TeV by the ATLAS detector, here we report evidence for light-by-light scattering. A total of 13 candidate events were observed with an expected background of 2.6 ± 0.7 events. After background subtraction and analysis corrections, the fiducial cross-section of the process Pb + Pb (γγ) right arrow Pb(∗) + Pb(∗)γγ, for photon transverse energy ET > 3 GeV, photon absolute pseudorapidity |η| < 2.4, diphoton invariant mass greater than 6 GeV, diphoton transverse momentum lower than 2 GeV and diphoton acoplanarity below 0.01, is measured to be 70 ± 24 (stat.) ± 17 (syst.) nb, which is in agreement with the standard model predictions.
AuthorsAaboud, M; Aad, G; Abbott, B; Abdallah, J; Abdinov, O; Abeloos, B; Abidi, SH; AbouZeid, OS; Abraham, NL; Abramowicz, H; Abreu, H; Abreu, R; Abulaiti, Y; Acharya, BS; Adachi, S; Adamczyk, L; Adelman, J; Adersberger, M; Adye, T; Affolder, AA; Agatonovic-Jovin, T; Agheorghiesei, C; Aguilar-Saavedra, JA; Ahlen, SP; Ahmadov, F; Aielli, G; Akatsuka, S; Akerstedt, H; Akesson, TPA; Akimov, AV; Alberghi, GL; Albert, J; Alconada Verzini, MJ; Aleksa, M; Aleksandrov, IN; Alexa, C; Alexander, G; Alexopoulos, T; Alhroob, M; Ali, B; Aliev, M; Alimonti, G; Alison, J; Alkire, SP; Allbrooke, BMM; Allen, BW; Allport, PP; Aloisio, A; Alonso, A; Alonso, F; Alpigiani, C; Alshehri, AA; Alstaty, M; Gonzalez, BA; Alvarez Piqueras, D; Alviggi, MG; Amadio, BT; Amaral Coutinho, Y; Amelung, C; Amidei, D; Amor Dos Santos, SP; Amorim, A; Amoroso, S; Amundsen, G; Anastopoulos, C; Ancu, LS; Andari, N; Andeen, T; Anders, CF; Anders, JK; Anderson, KJ; Andreazza, A; Andrei, V; Angelidakis, S; Angelozzi, I; Angerami, A; Anghinolfi, F; Anisenkov, AV; Anjos, N; Annovi, A; Antel, C; Antonelli, M; Antonov, A; Antrim, DJ; Anulli, F; Aoki, M; Bella, LA; Arabidze, G; Arai, Y; Araque, JP; Araujo Ferraz, V; Arce, ATH; Ardell, RE; Arduh, FA; Arguin, J-F; Argyropoulos, S; Arik, M; Armbruster, AJ; Armitage, LJ; Arnaez, O; et al.
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