Experimental and theoretical investigations on muon-to-electron conversion with the COMET experiment at J-PARC

• Applicants: Professor Dr. Dominik Stöckinger; Professor Dr. Kai Zuber
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 397660091

The study of elementary particles and fundamental interactions has revealed the crucial importance of symmetries and conserved charges. For example, electric charge is exactly conserved as a result of the fundamental gauge invariance of quantum electrodynamics. Lepton number is another charge, whose conservation however is not supported by any fundamental theory or symmetry. Charged leptons arise in three flavours (electron, muon, tau), and so far no violation of lepton flavour number has been observed. In the meantime the flavour change of quarks and flavour oscillations of neutrinos have been observed. Hence it is an essential question to probe charged lepton flavour violation as well. Typical models beyond the Standard Model, like supersymmetry, leptoquarks, and other extensions of the Standard model, indeed predict such a lepton flavour violation at potentially observable rates.The COMET experiment at J-PARC is a new experiment to probe lepton flavour violation. It focuses on the muon-to-electron conversion process on nuclei to search for this phenomenon. A dramatic improvement in sensitivity by 4 orders of magnitude is envisaged; currently no other experimental approach has such an improvement in sensitivity to new phenomena. Both applicants are collaboration members of COMET, and COMET will start datataking within the grant period, making this grant particularly timely. For the same reason, both applicants will perform shifts at the COMET experiment during the grant period. In this grant application sophisticated explorations of various supersymmetric and non-supersymmetric models with respect to the mentioned lepton-flavour violating process are performed. The phenomenological studies are accompanied by quantum field theoretical studies of required effective field theories and the construction of general computer software tools. A major experimental responsibility of the TU Dresden COMET collaborators is the muon capture normalisation measurement of COMET. The idea to determine this number is to measure muonic X-ray lines using a germanium detector. The respective development and commissioning and the final installation at JPARC is done by the Dresden group. In addition the Dresden group is responsible for the development and installation of the muon target. This TU Dresden work of this grant period will contribute significantly to the success of the COMET phase-I experiment. The collaboration has been created within the DFG-supported "strategic partnership" between Osaka (the leading university of the COMET experiment) and Dresden and within the excellence concept of TU Dresden.

• DFG Programme: Research Grants