A remarkable feature of the Standard Model is quark mixing, the ability of one quark flavour to transform into another. While this phenomenon is well-established, the model falls short of predicting the exact probabilities of these transmutations. Current analyses reveal a puzzling discrepancy: the probabilities of all possible mixings do not sum to 100%. This anomaly raises the possibility of new physics beyond the Standard Model.

To address this conundrum, Jordy de Vries of the University of Amsterdam's Institute of Physics, in collaboration with researchers from Los Alamos, Seattle, and Bern, has developed an innovative framework to precisely calculate the mixing of up and down quarks, the most prominent quark transmutation. Their findings were published in Physical Review Letters and highlighted as an Editor's Suggestion in Physical Review C.

The team's calculations draw on meticulous measurements of nuclear beta decays, a form of radioactive decay. The most reliable insights into up-down quark mixing come from superallowed beta decays - nuclear processes involving isotopes with no spin, making them theoretically simpler to analyze. However, these calculations are clouded by theoretical uncertainties stemming from the interplay of three fundamental forces: the strong nuclear force, electromagnetic interactions, and the weak force driving radioactive decay.

The newly developed framework effectively tracks this interplay, reducing theoretical uncertainties and revealing previously unaccounted-for effects of weak interactions within the nucleus. These effects currently dominate the computational uncertainties, but further refinements are on the horizon. Enhanced many-body nuclear calculations promise to tame these uncertainties, paving the way for physicists to uncover signals of new physics in nuclear processes.