Deep Underground Experiment Results Confirm Anomaly: Possible New Fundamental Physics

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New outcomes from the Baksan Experiment on Sterile Transitions (BEST) experiment verify anomaly suggesting new physics chance.

Sterile neutrino, physics fundamentals amongst interpretations of anomalous outcomes.

New scientific outcomes verify an anomaly seen in earlier experiments, which can level to an as-yet-unconfirmed new elementary particle, the sterile neutrino, or point out the necessity for a brand new interpretation of a side of ordinary mannequin physics, such because the neutrino cross part, first measured 60 years in the past. Los Alamos National Laboratory is the lead American establishment collaborating on the Baksan Experiment on Sterile Transitions (BEST) experiment, outcomes of which had been not too long ago printed within the journals Physical Review Letters and Physical Review C.

“The outcomes are very thrilling,” mentioned Steve Elliott, lead analyst of one of many groups evaluating the information and a member of Los Alamos’ Physics division. “This positively reaffirms the anomaly we’ve seen in earlier experiments. But what this implies shouldn’t be apparent. There are actually conflicting outcomes about sterile neutrinos. If the outcomes point out elementary nuclear or atomic physics are misunderstood, that will be very attention-grabbing, too.” Other members of the Los Alamos staff embrace Ralph Massarczyk and Inwook Kim.

cosmic science BEST Gallium Target

Located deep underground on the Baksan Neutrino Observatory within the Caucasus mountains in Russia, the finished two-zone gallium goal, at left, accommodates an internal and outer tank of gallium, which is irradiated by an electron neutrino supply. Credit: A.A. Shikhin

More than a mile underground within the Baksan Neutrino Observatory in Russia’s Caucasus Mountains, BEST used 26 irradiated disks of chromium 51, an artificial radioisotope of chromium and the three.4 megacurie supply of electron neutrinos, to irradiate an internal and outer tank of gallium, a gentle, silvery metallic additionally utilized in earlier experiments, although beforehand in a one-tank set-up. The response between the electron neutrinos from the chromium 51 and the gallium produces the isotope germanium 71.

The measured charge of germanium 71 manufacturing was 20-24% decrease than anticipated based mostly on theoretical modeling. That discrepancy is according to the anomaly seen in earlier experiments.

BEST builds on a photo voltaic neutrino experiment, the Soviet-American Gallium Experiment (SAGE), during which Los Alamos National Laboratory was a serious contributor, beginning within the late Eighties. That experiment additionally used gallium and high-intensity neutrino sources. The outcomes of that experiment and others indicated a deficit of electron neutrinos — a discrepancy between the expected and the precise outcomes that got here to be often called the “gallium anomaly.” An interpretation of the deficit could possibly be proof for oscillations between electron neutrino and sterile neutrino states.

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A set of 26 irradiated disks of chromium 51 are the supply of electron neutrinos that react with gallium and produce germanium 71 at charges that may be measured in opposition to predicted charges. Credit: A.A. Shikhin

The similar anomaly recurred within the BEST experiment. The doable explanations once more embrace oscillation right into a sterile neutrino. The hypothetical particle might represent an necessary a part of darkish matter, a potential type of matter thought to make up the overwhelming majority of the bodily universe. That interpretation might have additional testing, although, as a result of the measurement for every tank was roughly the identical, although decrease than anticipated.

Other explanations for the anomaly embrace the potential of a misunderstanding within the theoretical inputs to the experiment — that the physics itself requires transforming. Elliott factors out that the cross-section of the electron neutrino has by no means been measured at these energies. For instance, a theoretical enter to measuring the cross part, which is troublesome to verify, is the electron density on the atomic nucleus.

The experiment’s methodology was completely reviewed to make sure no errors had been made in elements of the analysis, comparable to radiation supply placement or counting system operations. Future iterations of the experiment, if carried out, might embrace a special radiation supply with increased power, longer half-life, and sensitivity to shorter oscillation wavelengths.


“Results from the Baksan Experiment on Sterile Transitions (BEST)” by V. V. Barinov et al., 9 June 2022, Physical Review Letters.
DOI: 10.1103/PhysRevLett.128.232501

“Search for electron-neutrino transitions to sterile states within the BEST experiment” by V. V. Barinov et al., 9 June 2022, Physical Review C.
DOI: 10.1103/PhysRevC.105.065502

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

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