Light-by-light scattering (γγ â 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 μ1of 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) â Pb(â )+ Pb(â )γγ,for photon transverse energy ET> 3GeV, photon absolute pseudorapidity |η| <2.4, diphoton invariant mass greater than 6GeV, diphoton transverse momentum lower than 2GeV 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.

Evidence for light-by-light scattering in heavy-ion collisions with the ATLAS detector at the LHC

Cavasinni, V.
;
Dell'Orso, M.
;
Donati, S.
;
Francavilla, P.;Roda, C.;Verducci, M.;
2017-01-01

Abstract

Light-by-light scattering (γγ â 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 μ1of 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) â Pb(â )+ Pb(â )γγ,for photon transverse energy ET> 3GeV, photon absolute pseudorapidity |η| <2.4, diphoton invariant mass greater than 6GeV, diphoton transverse momentum lower than 2GeV 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.
2017
Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Abeloos, B.; Abidi, S. H.; Abouzeid, O. S.; Abraham, N. L.; Abramowicz, H.; Abreu, H.; Abr...espandi
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/893052
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