New percent-level shift to the nucleon axial coupling discovered

Neutrons, when outside atomic nuclei, are unstable particles and have a short lifetime of approximately fifteen minutes. They undergo decay through the weak nuclear force, resulting in the formation of a proton, an electron, and an antineutrino. The weak nuclear force is one of the fundamental forces in the universe, along with the strong force, electromagnetic force, and gravitational force.

By comparing experimental measurements of neutron decay with theoretical predictions based on the weak nuclear force, scientists can potentially uncover new interactions that have not yet been discovered. However, achieving high levels of precision is crucial for this research. Recently, a team of nuclear theorists made an important discovery regarding neutron decay, specifically related to the interplay between the weak and electromagnetic forces.

This research revealed a significant effect on the strength of the weak nuclear force acting on a spinning neutron. This finding has two significant implications. Firstly, it confirms that systems and their mirror images do not behave identically due to the breaking of mirror reflection symmetry caused by the weak force. This has implications for the search for “right-handed currents,” which are hypothetical interactions that could restore mirror-reflection symmetry at very short distances. Secondly, the research highlights the need for more precise calculations of electromagnetic effects, which will require the use of advanced high-performance computers in the future.

The team of researchers conducted calculations to determine the impact of electromagnetic interactions on neutron decay, specifically considering the emission and absorption of photons (particles of light). This involved the collaboration of nuclear theorists from several institutions, including the Institute for Nuclear Theory at the University of Washington, North Carolina State University, the University of Amsterdam, Los Alamos National Laboratory, and Lawrence Berkeley National Laboratory. The results of their study were published in Physical Review Letters.

The calculations were performed using an efficient method called “effective field theory,” which helps organize the importance of fundamental interactions in phenomena involving strongly interacting particles. The researchers identified a new correction at the percent-level to the nucleon axial coupling, gA, which determines the strength of neutron decay. This correction arises from the emission and absorption of electrically charged pions, which are particles that mediate the strong nuclear force. While the effective field theory provides an estimate of uncertainties, further advancements in precision will necessitate advanced calculations using high-performance supercomputers provided by the Department of Energy.

The researchers also evaluated the impact of these findings on the search for right-handed currents. After considering the new correction, they found that experimental data and theory align well, and current uncertainties still allow for the possibility of new physics at relatively low mass scales.

Source: US Department of Energy

Leave a Comment