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Particle physics experiments

Results of deep underground experiments confirm anomaly: possible new fundamental physics

New results from the Baksan Barren Transformations Experiment (BEST) confirm an anomaly that points to new physical potential.

Sterile Neutrinos, Fundamentals of Physics among the explanations for abnormal results.

The new scientific findings confirm an anomaly seen in previous experiments, which could point to a new, as yet unconfirmed elementary particle, the sterile neutrino, or highlight the need for a new explanation for an aspect of Standard Model physics, such as the neutrino cross section, which was first measured 60 years ago. Los Alamos National Laboratory is the lead US institution collaborating on the Baksan Sterile Transformation Experiment (BEST), the results of which have recently been published in journals. Physical examination letters And the physical examination c.

“The results are very exciting,” said Steve Elliott, senior analyst for one of the teams evaluating the data and a member of the Los Alamos physics department. “This certainly confirms the anomalies we’ve seen in previous experiments. But what that means is unclear. There are now conflicting results on sterile neutrinos. If the results indicate a misunderstanding of basic nuclear or atomic physics, that would also be of interest. Other members of the Los Alamos team include Ralph Masarczyk and Enuk Kim.

Located deep underground at the Baksan Neutrino Observatory in Russia’s Caucasus Mountains, the completed two-region gallium target, left, contains an inner reservoir and an outer reservoir of gallium, which is irradiated by a source of electron neutrinos. Credit: AA Shikhin

Over a mile underground at the Baksan Neutrino Observatory in the Russian Caucasus Mountains 26 radioactive discs of Chromium 51, a man-made radioactive isotope of chromium and a 3.4 megapicury electron neutrino source, are best used for radiation of the internal and external tank of gallium, soft material, silver metal Also in previous experiments, although previously it was used in a single tank. The reaction between electron neutrinos from chromium 51 and gallium produces the isotope germanium 71.

The measured production rate of germanium-71 was 20-24% lower than predicted based on theoretical modeling. This discrepancy is consistent with the anomalies observed in previous experiments.

BEST is based on the solar neutrino experiment, the Soviet-American Gallium Experiment (SAGE), to which Los Alamos National Laboratory was a major contributor, beginning in the late 1980s. also used high-density gallium and neutrino sources. The results of this experiment and others indicated an electron neutrino deficiency – a discrepancy between expected and actual results that is known as the “gallium anomaly”. The explanation for the deficit could be evidence of oscillations between the states of electron neutrinos and sterile neutrinos.

chrome discs

An array of 26 radioactive chromium-51 disks is the source of electron neutrinos that interact with gallium and produce germanium-71 at rates that can be measured against expected rates. Credit: AA Shikhin

The same anomaly was repeated in the best experiment. Possible explanations again include oscillation in a sterile neutrino. A hypothetical particle may make up a significant portion of dark matter, a possible form of matter thought to make up the vast majority of the physical universe. This interpretation may require additional testing, as the measurement for each tank was nearly the same, although lower than expected.

Other explanations for the anomaly include the possibility that there is a misunderstanding in the theoretical input to the experiment – ​​that the physics itself needs reformulation. Elliott points out that the electron neutrino cross section has not been measured before at these energies. For example, the theoretical input for the cross section measurement, which is difficult to confirm, is the electron density in the atomic nucleus.

The methodology of the experiment was carefully reviewed to ensure that no errors occurred in certain aspects of the research, such as the placement of the radiation source or the operations of the counting system. Future iterations of the experiment, if performed, may include a different radiation source with higher energy, longer half-life, and sensitivity to shorter oscillation wavelengths.


“Results of the Baksan experiment on sterile transformations (better)” By VV Barinov et al., 9 Jun 2022, Available here. Physical examination letters.
DOI: 10.1103/PhysRevLett.128.232501

“Searching for electron-neutrino transitions to sterile states in the best experiment” By VV Barinov et al., 2022 Jun 9, Available here. physical examination c.
DOI: 10.1103/PhysRevC.105.065502

Funding: Department of Energy, Office of Science, Office of Nuclear Physics.