Light-by-light scattering (gamma gamma -> gamma gamma) 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 b1 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 PbCPb ( )!Pb./CPb(), for photon transverse energy ET>3 GeV, photon absolute pseudorapidity jj<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.

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

Chiodini, G;Gorini, E;Primavera, M;Spagnolo, S;Ventura, A;
2017

Abstract

Light-by-light scattering (gamma gamma -> gamma gamma) 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 b1 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 PbCPb ( )!Pb./CPb(), for photon transverse energy ET>3 GeV, photon absolute pseudorapidity jj<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.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11587/417698
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