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The article of the Baikal-GVD collaboration was published in the authoritative scientific journal Physical Review D. It published the first results of the search for astrophysical neutrinos based on data collected by the Baikal deep-sea neutrino telescope Baikal-GVD. The presence of an astrophysical neutrino flux, previously detected by the Antarctic neutrino telescope IceCube, has been confirmed. The Baikal neutrino Telescope is one of the Russian projects of the "megasience" level. It is being developed, including at the expense of the Ministry of Education and Science of the Russian Federation within the framework of state programs. The ceremonial launch of the Baikal-GVD telescope took place in March 2021 with the participation of the Minister of Education and Science of the Russian Federation Valery Falkov.

In the published article, the Baikal-GVD collaboration presented the results of measuring a diffuse neutrino flux of cosmic origin. The data for the last four years were analyzed. In total, 25 candidate events for neutrinos of astrophysical nature were identified. Their number and energy distribution are close to those expected from the diffuse flow recorded in the IceCube experiment. The scientific significance of this result lies in the fact that the existence of cosmic neutrinos is confirmed and that the parameters of the neutrino flux of two different experiments coincide within the limits of statistical and systematic uncertainties.

The Baikal-GVD neutrino telescope is the embodiment of the idea of the outstanding Soviet physicist, academician Moisei Alexandrovich Markov, expressed by him in 1960. He proposed to register neutrinos, "elusive" particles, in large volumes of water in natural reservoirs, where light detectors – photomultipliers will be located at a certain distance from each other.

Neutrino is a unique elementary particle without charge and with a very low mass. To interact with another particle, special conditions are needed: a neutrino interacts very weakly with matter. Somewhere in outer space, processes occur with a giant release of energy, neutrinos are born, fly through the Universe and do not interact with anything. When physicists register neutrinos on Earth, they can determine the direction from which the particle came, the energy that was at the place of its birth, and the type of neutrino: electron, muon or tau neutrino.

Neutrino telescopes in natural environments are actively used today to register and study ultrahigh-energy neutrino fluxes from astrophysical sources. The obtained data give physicists the opportunity to study cosmic processes with a huge release of energy, the features of the evolution of galaxies and the formation of supermassive black holes, as well as the mechanisms of particle acceleration.

In 1980, the Laboratory of High-Energy Neutrino Astrophysics was established at the Institute for Nuclear Research of the Russian Academy of Sciences (INR RAS) under the leadership of Corresponding Member of the Russian Academy of Sciences Grigory Vladimirovich Domogatsky. Its goal was to create a neutrino telescope in the waters of Lake Baikal and conduct physical research on it. Today, physicists from the Joint Institute for Nuclear Research (JINR, Dubna), Irkutsk State University (ISU) and a number of other domestic and foreign scientific organizations are actively participating in research on Lake Baikal together with scientists from the INR RAS.

Over the past 40 years, several neutrino telescopes have been created in the world. These were the first generation telescopes: NT-200 on Lake Baikal, AMANDA at the South Pole (successor to the 1976 DUMAND project) and ANTARES in the Mediterranean Sea. These installations made it possible to develop and implement a technique for detecting neutrinos in natural environments and to come close to creating telescopes of a cubic kilometer scale.

Two projects for the construction of neutrino telescopes are currently being implemented in the Northern Hemisphere: Baikal-GVD on Lake Baikal (3000 optical modules) and KM3NeT/ARCA in the Mediterranean Sea (378 optical modules).

The Baikal Neutrino Telescope is a unique scientific installation located 3.6 km from the shore at a depth of about 1300 m. Baikal-GVD is an effective multichannel astronomy tool for solving problems of neutrino astrophysics. The installation consists of 10 clusters, each cluster has 8 vertical garlands, each garland has 36 modules. The optical system registers the Cherenkov radiation of muons and cascades of high-energy charged particles generated in neutrino interactions.

In 2011, the IceCube detector was launched at the South Pole. About five thousand optical modules with sensitive photomultipliers inside were placed in the ice at a depth of more than two thousand meters.

In 2013, IceCube announced for the first time that it had discovered the existence of a total neutrino flux of cosmic origin from many sources – the so-called diffuse flux. However, such a significant result for the development of neutrino astronomy and astrophysics had to be confirmed by other experiments. This became the primary task of the Baikal-GVD and KM3NeT/ARCA neutrino telescopes in the Northern Hemisphere.

"The detection of a natural stream of high-energy neutrinos of astrophysical origin in an experiment by the IceCube Antarctic detector has now been confirmed by the results obtained in the Northern Hemisphere by the Baikal-GVD neutrino telescope. The joint work of these two detectors makes it possible to search for high–energy neutrino sources throughout the celestial sphere and serves as the beginning of the process of constructing a map of the neutrino sky," said Grigory Vladimirovich Domogatsky, Corresponding member of the Russian Academy of Sciences, Head of the Laboratory of High-Energy Neutrino Astrophysics of the Institute for Nuclear Research of the Russian Academy of Sciences, head of the Baikal-GVD collaboration.

Work on the deployment of the neutrino telescope continues. Every year, from mid-February to mid-April, expeditions take place on Lake Baikal, during which new clusters are established. In 2023, scientists plan to add two more clusters to the ten. It is expected that by 2027 Baikal-GVD will reach a volume of one cubic kilometer, equaling IceCube, and in the distant future – ten cubic kilometers.

"The discovery and measurement of the flow of extraterrestrial high-energy neutrinos by experiments at the South Pole and Lake Baikal, which are carried out in different hemispheres, under different conditions and show a close result, give us confidence that the joint work of these installations will allow us to study cosmic neutrino sources throughout the celestial sphere and will open the era of building a map of the starry sky in neutrinos", – said the head of the expedition for the deployment of the telescope, a researcher at the Laboratory of Nuclear Problems named after V.P. Dzhelepova of the Joint Institute for Nuclear Research Igor Anatolyevich Belolaptikov.

Information and image provided by the press service of the Institute for Nuclear Research of the Russian Academy of Sciences

Posted by Irina Usyk Information taken from the portal "Scientific Russia" (https://scientificrussia.ru/)

Image: Diagram of the Baikal-GVD neutrino Telescope | Baikal-GVD Collaboration