Scientists managed to deceive time and catch a ghost particle
Russian physicists, together with their American colleagues, managed to find confirmation of almost half a century of predictions that the so-called "ghost particle" neutrino interacts with ordinary matter. A study has been carried out that can help create a device that can see through nuclear reactors, as well as find out what processes occur inside supernovae.
In 1974, a theory was expressed among scientists about the possibility of interaction in some unknown way between neutrinos and matter. These elementary particles, millions of times lighter than an electron, can freely pass through the planets. Collisions with atomic nuclei occur periodically, and neutrinos interact with some neutrons and protons. But four decades ago, scientists made the assumption that an interaction is possible between the neutrino and the nucleus as a whole. This mechanism is called coherent neutrino scattering on nuclei. It was proposed as one of the components of the Standard Model of electroweak interactions, but has not been confirmed experimentally until now.
Electroweak interaction is a general description of several fundamental interactions - electromagnetic and weak. It is generally accepted that after the Universe reached a temperature of about 1015 kelvin (and this happened almost immediately after the Big Bang), these interactions were a single whole. Weak forces, in contrast to electromagnetic, manifest themselves on a much smaller scale relative to the size of the atomic nucleus. They provide for beta decay of the nucleus, in which it is possible to release not only neutrinos, but also antineutrinos. At the same time, according to the theory of electroweak interaction, not only a neutrino arises, but also its interaction with matter, matter.
The theory says that if an interaction process occurs between the neutrino and the nucleus due to coherent scattering, then energy is released, which is transferred to the nucleus through the Z-boson, which is the carrier of weak interaction. It is very difficult to fix this process, because the energy release is very insignificant. To increase the probability of coherent scattering, heavy elements are used as targets, in particular, cesium, iodine and xenon. At the same time, the heavier the core, the more difficult it is to detect this recoil, which, in turn, also complicates the situation.
Scientists proposed using cryogenic detectors to detect neutrino scattering, theoretically capable of recording even the interaction of simple matter and dark matter. A cryogenic detector is a very cold chamber, with a temperature just a hundredth of a degree above absolute zero, and which captures the small amount of heat that is released during the reaction of nuclei with neutrinos. Crystals of calcium or germanium tungstate are used as a substrate; in addition, superconducting devices, inert liquids or modified semiconductors could also play the role of detectors.
After performing the necessary calculations, the researchers found that the ideal candidate for the target is cesium iodide with impurities of sodium. It was the crystals of this substance that became the basis for the small detector (its weight was only 14 kilograms, and the size was 10x30 centimeters). This detector was installed at the SNS neutron source, which is located in the US state of Tennessee, at the Oak Ridge National Laboratory. The detector was placed in a tunnel shielded with concrete and iron, about two dozen meters from the source, which reproduces neutron beams, but at the same time there is a side effect - neutrinos.
An artificial source SNS, in contrast to natural sources of neutrinos, in particular, the Earth's atmosphere or the Sun, is capable of producing a sufficiently large neutrino beam to be captured by a detector, but at the same time small enough to cause coherent scattering. As the researchers note, the detector and the source fit together almost perfectly. Cesium iodide molecules, when interacting with particles, are converted into scintillators (in other words, they re-emit energy in the form of light). And it was this light that was registered. According to the Standard Model, a muonic neutrino, an electron neutrino, and a muonic antineutrino entered into interaction with the crystal.
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This discovery is important. And the point is not at all that scientists have once again confirmed the physical picture of the world, which the Standard Model describes. Through coherent scattering, scientists hope to develop specific tools and techniques for monitoring nuclear reactors to help see through walls what is happening inside. In addition, coherent scattering occurs inside neutron and ordinary stars, as well as during supernova explosions. Thus, it will provide an opportunity to learn more about their structure and life. Scientists know that the neutrinos present in the bowels of supernovae hit the outer shell during the explosion, forming a shock wave that tears the star into pieces. Due to coherent scattering, a similar interaction between neutrinos and the matter of the star that explodes can be explained.
In addition, in the search for WIMPs - theoretical particles of dark matter - researchers rely on detecting radiation that arises from their collision and atomic nuclei. It must be distinguished from the background that creates coherent neutrino scattering. This can improve the data that can be obtained about dark matter using cryogenic and other detectors.