Anomalies in semileptonic b decays as antennas of New Physics

• Applicant: Dr. Danny van Dyk
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2017 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 328776644

The Standard Model (SM) of particle physics is a very successful theory that has withstood many experimental tests. However, it cannot explain some intriguing observations, such as non-vanishing neutrino masses or the baryon-antibaryon asymmetry in the universe. Particle physics therefore expects to replace the SM with a new unknown theory, which explains all present observations. Quark Flavor Physics provides powerful tools to probe both the SM and potential replacements at very high energies or, equivalently, very short distances (SD). One of its most interesting tools are flavor-changing semileptonic b-quark decays. These decays are mediated by virtual quantum effects, and are therefore sensitive to particles that are too heavy to be produced directly. Consequently, they provide important information that is complementary to direct searches for new interactions and particles, which are carried out at the Large Hadron Collider.My proposal aims to improve the understanding of SD interactions in semileptonic b decays, and I will address two key issues that presently inhibit progress: reduction of the uncertainties associated with hadronic physics; and development of methods to combine experimental and theoretical inputs in global analyses. One of the major sources of hadronic uncertainty arises from the lack of understanding of charm-induced long-distance effects. My research will, for the first time, combine experimental results on multiple exclusive decays to overconstrain the relevant hadronic matrix elements. Correlations between the measurements must be accounted for, which requires both experimental and theoretical developments. The results will enable me to better separate SD from hadronic effects, which present global analyses cannot disentangle. The other major source of hadronic uncertainty is the incomplete knowledge of the hadronic form factors in amplitudes for exclusive rare b-hadron decays. I will combine non-perturbative methods such as Hadronic Dispersion Relations and Light-Cone Sum Rules with experimental measurements to determine these form factors. In order to make this determination, it is essential to fully exploit the experimental data, including further dedicated measurements. Moreover, complete use of the high precision results from upcoming high-luminosity experiments will require analyses to include all available theoretical and experimental correlations. Previous analyses rely on my EOS software, which ispublicly available. I will further develop EOS, and extend it with all physics results that my project produces.Having gained a better understanding of the SD effects, the project will seek to increase confidence in present and emerging results by ascertaining the existence of models that can produce such effects. Ultimately, I expect that my research will allow me to either find evidence for new phenomena in quark flavor physics, or to place the most stringent bounds on the size of any new physics effects.

• DFG Programme: Independent Junior Research Groups
• International Connection: Switzerland
• Cooperation Partner: Dr. Javier Virto