Search for unknown phenomena in rare charm hadron decays

• Applicant: Dr. Dominik Mitzel
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 464412659

The Standard Model of particle physics has successfully described the elementary particles and their interactions for more than 50 years. Despite the existence of fundamental questions that cannot be explained within the Standard Model, there is no significant experimental result that is incompatible with its predictions. Famous limitations are the lack of a suitable dark matter candidate and the explanation of the observed matter-antimatter asymmetry within the universe. Consequently, the field of particle physics tries to find hints for unknown phenomena that point towards extensions of the Standard Model, also known as “new physics”. Rare decays of unstable hadrons with heavy quark content are particularly sensitive to contributions of unknown particles. The LHCb experiment at the LHC (CERN) is specialised in precision measurements of beauty and charm hadrons and has recorded the word’s largest data set of decays of these hadrons. Via quantum corrections, heavy new particles can change the rates of rare decays, modify angular distributions of the decay products and induce effects that might lead to particle-antiparticle differences. With this approach, the mass scale of new particles is not limited by the collision energy of the LHC. Rare decays of hadrons containing beauty or strange quarks have been investigated for long. On the other hand, rare decays of charm hadrons are largely unexplored. The reasons for this are both an exceptional suppression and challenges in the theoretical description of the decays which often lead to uncertainties in the Standard Model predictions. Recently, theoretical physicists have pointed out that unique symmetries within the charm system allow for the definition of various observables, which are clean null-tests of the Standard Model with negligible uncertainties in the theoretical predictions. At the same time, precise experimental investigations of rare charm decays become possible at LHCb for the first time ever. This opens the door to a promising and largely unexplored field.In this project, null-test measurements will be performed in the context of angular analyses, measurements of particle-antiparticle asymmetries, and by comparing the properties of rare decays with leptons of different generations. The measurements have the potential to discover new physics or significantly constrain the parameter space of promising theories and new particles such as leptoquarks and Z’ bosons. Decays of charm hadrons offer the unique opportunity to find unknown phenomena that are complementary to the measurements in the B and kaon system and will play a key role in future searches.Within this project, innovative concepts for the real-time analysis of the LHCb data and machine learning algorithms will be developed that will be essential for the success of the project.

• DFG Programme: Independent Junior Research Groups
• International Connection: Switzerland
• Cooperation Partners: Dr. Marianna Fontana; Dr. Alex Pearce; Dr. Sascha Stahl