Precision Constraints on CP Violation in the Higgs Sector

• Applicant: Dr. Joachim Brod
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 372843874

The history of our universe and the nature of the matter that it contains are among the most fundamental questions of the natural sciences. Modern high-energy physics allows to address both questions in a unique way.Today's particle physicists understand the physical processes that can be probed in experiments at particle colliders very well. The current knowledge is summarized in the "Standard Model of Particle Physics", developed in the seventies of the last century and verified since then, last by the spectacular discovery of the Higgs boson at the Large Hadron Collider (LHC) at CERN near Geneva, the most powerful particle collider ever built.Yet, the Standard Model fails to explain the observed amount of baryons (the fundamental constituents of visible matter -- for instance, atomic nuclei) in the universe by many orders of magnitude. One of the reasons is that the predicted difference between particles and antiparticles (also called CP violation) is too small. However, non-standard interactions of the Higgs boson with the standard model particles can generate sufficient CP violation -- such interactions are not yet ruled out experimentally.These hypothetical new interactions are very difficult to observe at the LHC. Interestingly, via quantum effects they can induce small characteristic changes in the response of neutrons to electromagnetic fields. Thus, precision measurements provide an alternative and powerful way to discover these new interactions.My proposed work aims to maximize the impact of these precision probes.In order to interpret the experimental results, it is essential to have a solid understanding of the microscopic physical processes underlying the precision observables. Thus, my first goal is to substantially improve the current theoretical predictions. This is expected to increase the sensitivity reach of the precision experiments by up to a factor of ten.Moreover, the physics required to provide sufficient CP violation in the early universe can leave an imprint also on meson decays. This creates a new connection between precision nuclear and flavor physics -- the same underlying processes can manifest themselves in many different ways. This complementarity has barely been explored until now. It will also allow us to interpret the measurements done at LHCb or Belle II in a new context.Hence, my second goal is to systematically look for new precision flavor observables that are sensitive to the new CP violating interactions needed for baryogenesis.Finally the obtained results will be combined and applied to specific models that can explain the matter content of the universe.

• DFG Programme: Research Grants