Russian physicists have shown that elastic coherent scattering of reactor antineutrinos on xenon nuclei cannot exceed the Standard Model prediction by more than 60–90 times. To do this, they used the RED-100, a two-phase emission detector filled with liquid xenon located near the nuclear reactor of the Kalinin Nuclear Power Plant. An article about the study is available on the preprint portal arXiv.org.
Elastic coherent scattering of neutrinos and antineutrinos on atomic nuclei is the most probable process of interaction of these particles with matter in the energy range of up to several tens of megaelectronvolts. The cross-section of such interaction is tens and even hundreds of times greater than the cross-section of inverse beta decay. Therefore, scientists have high hopes for this process, believing that it will allow monitoring nuclear reactors and control over the non-proliferation of nuclear weapons using compact neutrino detectors. However, the magnitude of the detectors' response to such scattering is extremely small, and it was possible to register it only in 2017 in an accelerator experiment thanks to the development of technology, despite the fact that it was predicted about 50 years ago.
We have already written recently that two liquid xenon detectors were able to see (once, twice) this process from solar neutrinos, but both of them have a large mass of the detecting substance, on the order of several tons, and are located in low-background underground laboratories. Registration of coherent scattering of reactor antineutrinos is a much more difficult task due to the higher external radiation background. For example, CONUS, one of the most advanced reactor experiments in this area, has not yet seen this process.
A group of physicists led by Alexander Bolozdynya (AI Bolozdynya) from the Moscow Engineering Physics Institute obtained the first limitation of this process on xenon nuclei for reactor antineutrinos. For this, the scientists used a two-phase emission detector filled with liquid xenon with a mass of about 130 kilograms in the active volume. The detector was located 19 meters from the nuclear reactor of the Kalinin Nuclear Power Plant and was surrounded by passive protection from external radiation background, consisting of layers of copper and water.
To detect the excess of the detector count rate caused by signals from antineutrinos, the physicists compared the data collected during the periods when the reactor was switched off and on. During the data analysis, the scientists managed to additionally suppress the external background by several orders of magnitude. However, this was not enough to register the difference in the detector count rates depending on the reactor operation. However, this allowed the physicists to establish the first limit on the process of elastic coherent scattering of reactor antineutrinos on xenon nuclei, which turned out to be 60-90 times greater than the Standard Model prediction.
Scientists note that it is possible to register the process of elastic scattering of reactor antineutrinos using the RED-100 detector if xenon is replaced by argon, in which a smaller amount of specific background is expected. To test this hypothesis, physicists are already conducting technical tests at MEPhI.
Scientists are studying neutrino interactions in various energy ranges. For example, we recently wrote that physicists have probably registered a neutrino with a record energy of tens of petaelectronvolts.