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;
2017-01-01
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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
