The Standard Model of particle physics is our most complete theory of the microscopic world and has passed numerous experimental tests over the last decades. At the same time it cannot be a complete theory of nature, not least because the particles and forces in the Standard Model cannot explain macroscopic phenomena such as dark matter or the matter-antimatter asymmetry of the universe. Lepton universality is a fundamental, although accidental, symmetry which states that the electroweak force mediators couple equally to all three generations of leptons. It has a wide range of straightforward and theoretically robust experimental consequences, and can therefore be used to construct particularly powerful null tests of the Standard Model of particle physics. I will discuss a recent publication by the LHCb experiment of a particular type of this null test: the measurement of electron-muon universality in beauty to strange quark transitions. I will describe the experimental aspects of this measurement, discuss the differences with respect to previous lepton universality tests, and draw some conclusions for the future.
Quantum entanglement, foundations and experiments
Prof. Dr. Anton Zeilinger
Nobel laureate in physics in 2022
University of Vienna, Austrian Academy of Sciences, Austria
