The first stage of the construction of Baikal-GVD neutrino telescope, one of the largest in the world, has just been finished. It aims at observing neutrinos from astrophysical sources. Physicists from INP PAS in Kraków also take part in this project.
The neutrino astronomy is a new field in physics that has been constituted in the previous decade by the observations of first events of high-energy astrophysical neutrinos by the IceCube telescope at Antarctica. Neutrinos are elementary particles that interact with matter very weakly and, consequently, very rarely. Thanks to that, they carry an undistorted picture of their source that can be located very far away. On the other hand, a neutrino is very hard to detect so detectors with active volumes of the order of a cubic kilometer are needed.
The Baikal-GVD telescope is such a detector, its active volume is currently approximately 0.5 km3 and is located in the clean waters of the Baikal lake at Siberia. Its construction is still ongoing towards the foreseen active volume of 1 km3. The goal of the telescope is to record signals from secondary particles appearing in the aforementioned rare interactions of neutrinos. Those signals are light flashes of the so-called Cherenkov radiation.
The telescope is a set of elements designed to detect such flashes, the so-called photomultipliers. They are grouped in 8 lines, 36 photomultipliers per each. Those lines are anchored to the lakebed and end with buoys (around 60m below the surface) that span the lines upwards. Such a set of 8 lines is called a cluster. Currently, there are 8 clusters in operation.
The location of the telescope has many advantages. The Baikal lake is a unique reservoir of freshwater with a depth exceeding 1 km and with almost flat lakebed. A very special feature of Baikal is the fact that it freezes seasonally and the thickness of ice cover exceeds 60 cm (often reaching 120 cm). This allows the use of heavy equipment, like trucks, tractors and all-terrain vehicles in the construction and maintenance works at the detector during winter expeditions that usually take place from mid-February to early April. This is much easier and much cheaper in comparison to the use of research vessels with specialized crews. The physicists from INP PAS had also taken part in the winter expeditions and construction works.
The Baikal-GVD telescope aims mainly at the observation of neutrinos from astrophysical sources. They can be either extragalactic, such as Active Galactic Nuclei, Gamma-Ray Bursts, blazars, etc. The sources can also be intergalactic such as the Sgr A* black hole. The telescope is sensitive to all three neutrino flavors.
Baikal-GVD is not the only such telescope present in the world. The aforementioned IceCube detector, located in the Antarctic ice has been taking data since 2010. It is however mostly aimed at observing the northern sky hemisphere, whereas the Baikal-GVD “is looking” south. Another south-looking telescope is the KM3Net detector in the Mediterranean Sea, however its active volume is currently still much smaller.
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