The Buxon Experiment on Sterile Infection (BEST) investigates the possible connection of the gallium anomaly and oscillations between active and sterile neutrinos. The latest results from BEST confirm a discrepancy seen in previous experiments. This could indicate an as yet unconfirmed new elementary particle, the sterile neutrino, or indicate the need for a new interpretation of an aspect of Standard Model physics, such as the neutrino cross-section.
Using 26 irradiated disks of chromium 51, a synthetic radioisotope of chromium, and a 3.4 megacury source of electron neutrinos, Best irradiated an inner and outer tank of gallium, a soft, silvery metal also used in previous experiments. Although the first one-tank installation. The isotope germanium 71 is created through the reaction of electron neutrinos from chromium 51 and gallium.
Based on theoretical modeling, the measured rate of germanium 71 production was 20–24% lower than expected. This disparity corresponds to the discrepancy of the previous experiment.
BEST is based on the Soviet-American Gallium Experiment (SAGE), a solar neutrino experiment to which Los Alamos National Laboratory contributed significantly in the late 1980s. Gallium and high-intensity neutrino sources were also used in the experiment. The results of that and other investigations revealed a lack of electron neutrinos, a difference between expected and observed results known as the “gallium anomaly”. The reduction can be interpreted as evidence of oscillations between the electron neutrino and sterile neutrino states.
The same discrepancy was repeated in the BEST experiment. Possible explanations again include oscillations in a sterile neutrino. The hypothetical particle may be an essential part of dark matter, a possible form of matter thought to make up the vast majority of the physical universe. However, that interpretation may require further testing, as the measurements for each tank were approximately the same, although less than expected.
Other possibilities for the discrepancy include misinterpretation of the theoretical inputs of the experiment or reworking the physics. According to Elliott, the cross-section of electron neutrinos at these energies has never been measured. For example, the electron density in an atomic nucleus is a theoretical input for cross-section calculations that are difficult to establish.
The scientists reviewed the methodology of the experiment to ensure that there were no errors in aspects of the research, such as radiation source placement or counting system operation. Future iterations of the probe, if carried out, may include a different radiation source with higher energy, longer half-life, and sensitivity to shorter oscillatory wavelengths.
Journal Reference:
- VV Barinov et al., Sterile infection from the Bakson experiment (BEST), Results of Physiological Review Letters (2022). DOI: 10.1103/PhysRevLet.128.232501
- Discover the electron–neutrino transition to sterile states in VV Barinov et al., Best Experiment, Physical Review C (2022). DOI: 10.1103/PhysRevC.105.065502
