Beyond the TeV scale: from the Higgs boson to rare pion decays

Synopsis

Precision measurements at the intensity and energy frontiers provide a unique opportunity to reveal new physics effects at scales much beyond those we can access directly. I will present two avenues of such measurements exploring the relationship between the three generations of matter and the interactions that govern them. The first measurement employs the ATLAS experiment at the LHC where the tau lepton, a peculiar cousin of the electron, offers the opportunity to study the Yukawa interaction. Mediated by the Higgs boson, the Yukawa interaction is the only one known to act differently for each generation of matter. I will present the strategy employed by the ATLAS experiment to overcome the challenges that detecting tau leptons entails, discuss the latest results on the tau Yukawa and expectations for the forthcoming runs of the LHC. The second avenue makes use of rare pion decays, a pristine probe of lepton flavor universality and quark mixing. PIONEER, a next-generation experiment proposed at the Paul Scherrer Institute, is set to improve the precision of rare pion decays ten-fold over current experiments. I will give an overview of the project and present the challenges and promises of the detector design.