27 Jun/24
11:00 - 13:00 (Europe/Zurich)

Light-by-light scattering


4/2-011 at CERN

Light-by-light scattering is a rare QED-loop process in which two photons interact and change direction. This process is not only interesting by itself but may be sensitive to contributions from particles beyond the Standard Model. Direct evidence for this process at high energy had proven elusive for decades, until the LHC began its second data-taking period (Run 2). Collisions of lead ions in the LHC provide a uniquely clean environment to study light-by-light scattering. When ultra-relativistic lead ions meet at the centre of the detector, they generate enormous fluxes of photons which may interact with each other. Such interactions, where there is no overlap between the two ions, are known as ultra-peripheral collisions. They provide huge amplification for photon-induced processes, enabling observation of the extremely rare light-by-light scattering.
In this talk, we review a series of ATLAS and CMS measurements on light-by-light scattering, including interpretations for specific beyond the Standard Model scenarios.  

Mateusz Dyndal is an experimental physicist working on the ATLAS experiment. He obtained his PhD at AGH University of Krakow and Universite Paris-Saclay in 2015, where he studied two-photon interactions in pp collisions with ATLAS. He then held postdoctoral positions at DESY and CERN, where he contributed to the measurements of light-by-light scattering in Pb+Pb, inclusive W+W- production in pp collisions and to the search for the Higgs boson Dalitz decay. He is now an associate professor at AGH University of Krakow, where he continues his involvement with the ATLAS physics program, including the exploration of ultra-peripheral collisions.


Jeremi Niedziela is an experimental physicist who obtained his PhD at the Warsaw University of Technology for his first-ever measurement of the strong interaction parameters for baryon-antibaryon pairs containing strange quarks. Upon defending his PhD thesis, he was selected for the CERN Research Fellow program, and at that time he moved to CMS to pursue his dream of searching for new physics. Since then, he's worked on light-by-light scattering and searches for Axion-Like Particles, searches for supersymmetric particles via disappearing tracks, as well as, during his PostDoc at ETH Zurich, exploiting machine learning to search for Dark Sectors through semivisible jets. Currently, Jeremi is a Fellow at DESY, where he continues his involvement in searches for new physics - among other topics are searches for Axion-Like Particles in events with top-antitop quark pairs.