On January 13, 2025, scientists at CERN announced a groundbreaking discovery regarding light-by-light scattering, a phenomenon predicted by quantum physics. This research has significant implications for our understanding of electromagnetism and the search for new particles.
Typically, when two beams of light intersect, their photons pass through each other without interaction. However, under specific conditions, photons can interact, creating temporary charged particles that annihilate back into photons. This rare event, known as light-by-light scattering, was theorized by pioneers like Enrico Fermi and Richard Feynman and is crucial for testing quantum electrodynamics (QED).
The CMS collaboration at the Large Hadron Collider (LHC) successfully isolated 26 instances of light-by-light scattering in lead-lead collisions, far exceeding the expected background events. This observation, with a statistical significance of five standard deviations, confirms that such interactions can occur at colliders, reinforcing the validity of the Standard Model of particle physics.
Aside from validating existing theories, these findings open avenues for exploring new particles that primarily interact with photons, such as axion-like particles (ALPs). The CMS results provide constraints on the mass and coupling of these hypothetical particles, potentially guiding future searches in particle physics.
As the LHC continues to generate more data, enhancements to the CMS detector, including a new high-granularity calorimeter, will facilitate deeper investigations into light-by-light scattering and its implications for both theoretical and experimental physics.