ATLAS sees first direct evidence of light-by-light scattering at high energy

Physicists from the ATLAS experiment at CERN have found the first direct evidence of high energy light-by-light scattering, a very rare process in which two photons – particles of light – interact and change direction. The result, published in Nature Physics, confirms one of the oldest predictions of quantum electrodynamics (QED).

Direct evidence for light-by-light scattering at high energy had proven elusive for decades – until the Large Hadron Collider’s second run began in 2015. As the accelerator collided lead ions at unprecedented collision rates, obtaining evidence for light-by-light scattering became a real possibility. “This measurement has been of great interest to the heavy-ion and high-energy physics communities for several years, as calculations from several groups showed that we might achieve a significant signal by studying lead-ion collisions in Run 2,” says Peter Steinberg, ATLAS Heavy Ion Physics Group Convener.

Five RCPTM scientists are members of the CERN-ATLAS Collaboration: L. Chytka, P. Hamal, M. Hrabovsky, J. Kvita & L. Nozka.