The quarks that form the nuclei of all atoms around us are known to “mix,” meaning they occasionally transform from one type to another. However, the exact frequencies of these transformations remain uncertain, and intriguingly, theoretical predictions don’t add up to 100%. Physicist Jordy de Vries from UvA-IoP and collaborators from Los Alamos, Seattle, and Bern have published new research that takes an important step toward unraveling these mysteries.

Good things often come in threes, and the Standard Model of particle physics is no exception. It organizes elementary particles into three “generations.” Take quarks, for example. The first generation includes the “up” and “down” quarks, which form the building blocks of atomic nuclei. Beyond these, two additional pairs exist: “charm” and “strange” quarks, as well as “top” and “bottom” quarks. Together, these six varieties are called the six quark flavors.

The Standard Model predicts that quark flavors can transmute into one another in a process called quark mixing. However, it doesn’t specify how frequently these transformations occur. Intriguingly, recent analyses reveal a discrepancy: the probabilities of all possible quark mixings don’t add up to 100%. What could this mean? Is it a sign of physics beyond the Standard Model?

To answer this question, UvA-IoP physicist Jordy de Vries and colleagues from Los Alamos, Seattle, and Bern have developed a new framework and performed associated calculations to very precisely determine the amount of mixing between up and down quarks, for which the effect is strongest.

The work was recently published jointly in Physical Review Letters and as an Editor’s Suggestion in Physical Review C.

As input for the calculations, the physicists use precise measurements of radioactive decay processes known as nuclear beta decays. The most accurate determination of the up-down quark mixing comes from so-called superallowed beta decays, occurring across the chart of nuclear isotopes. “Superallowed” means that the involved nuclei have no spin and are therefore easier to describe theoretically.

Nevertheless, the calculation of the amount of mixing from the extremely precise data suffers from a theoretical uncertainty due to the subtle dance between the three fundamental forces of nature that are involved in the process: the strong nuclear force, the electromagnetic interaction, and the weak process that causes the radioactive decay.

The new framework was designed to track this interplay and tame the theoretical uncertainty. It led the physicists to uncover effects involving the weak interactions between the constituents of the nuclei that had not been considered before. These effects currently dominate the uncertainty in the computations.

In the near future, building on this work and on advanced many-body nuclear calculations, the uncertainties will be brought under control, thus opening the way to uncover possible footprints of new physics in nuclear processes.