Light-by-Light Scattering (Project LBL)

• Applicants: Professor Harvey Byron Meyer, Ph.D.; Vladimir Pascalutsa, Ph.D.
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 458854507

Interactions between photons and, in particular, the scattering of light by light (LbL) are effects of purely quantum origin. In classical electrodynamics, the linearity of Maxwell's equations precludes such processes from occurring. In the Standard Model (SM) of particle physics, LbL scattering arises dynamically through the virtual effects of charged particles. In the language of Feynman diagrams, these effects are described by charged-particle loops.The first direct observation of light-by-light scattering has recently been made at the Large Hadron Collider (LHC) at CERN, Geneva in the peripheral collisions of lead ions. The interpretation of LbL scattering at the LHC requires an accurate theoretical description of the underlying SM processes. At present this interpretation is done using a Monte-Carlo event generator called Superchic, where only the one-loop contributions, involving the charged particles of the SM, are implemented. This description will need to be refined as the accuracy of experimental data is improving. Within the project LBL, we aim to develop the theoretical description of the `hadronic' contributions, i.e. those associated with the subatomic strong interaction, responsible for nuclear binding. The improved description will be implemented in Superchic. In collaboration with colleagues from the ATLAS experiment at LHC, these theoretical developments will allow us to analyze and interpret the new data on LbL scattering from Pb-Pb collisions.Furthermore, the theoretical description of the LbL amplitude will be validated by a direct calculation of the forward LbL amplitudes from first principles based on the framework of lattice QCD. The calculations will be performed at space-like photon virtualities. In this project, we aim to significantly improve on our previous calculations of these amplitudes, by using more realistic quark masses in the simulations and higher statistics, as well as by extrapolating the lattice spacing used in the simulations to zero in a controlled manner.

• DFG Programme: Research Units
• Subproject of: FOR 5327: Photon-photon interactions in the Standard Model and beyond - exploiting the discovery potential from MESA to the LHC
• International Connection: Switzerland
• Co-Investigators: Dr. Kristof Schmieden; Professor Dr. Matthias Schott
• Cooperation Partner: Dr. Jeremy Green