New precise calculation of nuclear beta decays paves the way to uncover physics beyond the standard model
Theorists identify new effects needed to compute the nuclear beta decay rate with a precision of a few parts in ten thousand.
image: In nuclear beta decay an up quark ‘u’ in a proton converts into an up down quark ‘d,’ turning the proton into a neutron and emitting a positron and a neutrino. This work affects interpretation of beta decay measurements across the chart of nuclides.
Credit: Image courtesy of Vincenzo Cirigliano
The Science
Quarks are the fundamental building blocks of matter and come in six flavors. The “up” and “down” flavors make up neutrons and protons. Through the weak nuclear force, one quark flavor can transmute into another. However, there’s something strange afoot in this process. Current data and theory indicate that the probabilities of quark transmutation do not add up to 100%, as predicted by the Standard Model of Particle Physics. Instead, there is a deficit of about a part in a thousand. To understand whether this is due to new physics beyond the Standard Model or underestimated uncertainties, a team of nuclear theorists has laid out a new framework needed to extract the up-down quark flavor mixing (the largest mixing) with a precision of a few parts in ten thousand from certain nuclear beta decays. The new framework is designed to track the subtle quantum-mechanical interplay between the strong nuclear force, the electromagnetic interaction, and the weak force that causes the radioactive decay.
The Impact
The ultimate goal of this research is to confirm the validity of Standard Model down to distances on the order of one millionth of the proton radius or to discover new physics beyond the Standard Model. To do so, scientists must reach high precision in both experiments and theory. By uncovering new effects involving the weak interactions of pairs of neutrons and protons, this work is a key step towards achieving a theoretical uncertainty of few parts in ten thousand in the predictions of nuclear beta decay rates. Researchers are applying the new framework in state-of-the-art calculations of the structure of atomic nuclei.
Summary
Precision studies of the beta disintegration of atomic nuclei provide stringent tests of the weak nuclear force, encoded in the Standard Model, and probe the existence of as yet undiscovered particles and forces. State-of-the-art studies point to a discrepancy between experimental data and the expectations of the Standard-Model. Could this be a signal of new physics beyond the Standard Model? To answer this question, a team of six nuclear theorists from three universities and one national laboratory has developed a new framework to compute the rate for nuclear beta decays with a precision of a few parts in ten thousand. Along the way, the team identified previously unaccounted effects that arise from the interplay of the strong, weak, and electromagnetic forces.
In the future, building on this work and on advanced many-body nuclear calculations will help scientists control uncertainties at the level of a few parts in ten thousand, thus opening the way to uncover possible footprints of new physics in nuclear beta decays. Should the current discrepancy with Standard Model be confirmed, it would point to the existence of new particles of mass up to ten thousand times the proton mass. This mass is far above the direct reach of existing high-energy particle colliders.
Funding
This research was supported by the Department of Energy Office of Science, Office of Nuclear Physics, and Office of High Energy Physics; the Laboratory Directed Research and Development program at Los Alamos National Laboratory; the National Science Foundation; the Dutch Research Council; and the Swiss National Science Foundation.