Searching for New Physics with rare B decays

• Applicant: Dr. Christoph Langenbruch
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2016 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 315226040

The aim of the Emmy-Noether group is the search for phenomena beyond the Standard Model of particle physics in rare B decays. While the Standard Model describes the fundamental building blocks of matter and their interactions to high precision it is known to be incomplete, as it exhibits several shortcomings; it does for example not contain a dark matter candidate. Extensions of the Standard Model that address these open questions are referred to as New Physics and generally require the introduction of new heavy particles. Rare B decays constitute powerful probes for New Physics effects, as they are heavily (loop-and CKM) suppressed in the Standard Model. New heavy particles can significantly contribute to these decays and change their rates, as well as the angular distributions of the final state particles. As the heavy new particles contribute as virtual particles, these searches are not limited by the available beam energy, and can thus be sensitive to higher mass scales than direct searches. Several tensions currently exist between data and Standard Model predictions in the area of rare B decays, the so-called flavour anomalies. The Emmy-Noether group has already delivered important contributions to this area, most notably through an updated angular analysis of the decay of a B-meson into a K*-meson and a di-muon pair. This analysis of LHCb data confirms a tension with the Standard Model reported earlier and slightly increases its significance. Also a new and more powerful method to analyse this decay was devised in the group, its application to LHCb data is currently in preparation. For the sixth year of the Emmy-Noether group, the ongoing program will be extended to include a measurement of the isospin asymmetry A_I(B->Kmumu), an observable in which hadronic uncertainties largely cancel and which can thus be precisely predicted in the Standard Model. Furthermore, a search for Majorana neutrinos in lepton-number violating B decays will be performed. The striking same-sign lepton signature that could be induced by Majorana neutrinos would constitute a clear sign of New Physics. Finally, the multivariate di-lepton trigger developed by the Emmy-Noether group will be tested, tuned and optimised for the start of the LHC physics Run 3. The proposed research builds on the extensive work already performed in the Emmy-Noether group and extends the program to new measurement that will result either in clear signs of New Physics or stringent constraints for New Physics contributions. The work proposed on the trigger will be essential to fully exploit the physics potential of the large data samples that will be taken during the LHC Run 3.

• DFG Programme: Independent Junior Research Groups