Physicists have recorded, for the first time in history, "ghost" neutrino particles produced by collisions inside the Large Hadron Collider (LHC), the largest and most powerful particle accelerator to date. Control signals indicating the presence of these particles were recorded by the sensors of the FASER experiment. And further study of the events and the collected data will allow scientists to better understand some aspects of particle physics.
Let us remind our readers that neutrinos are very light elementary particles that do not have an electric charge, which rarely interact with particles of ordinary matter. The rarity of interactions makes the process of detecting neutrinos very difficult, even if such particles are very common and their huge number, amounting to billions, pass through the human body every second. It is because of this elusive nature that neutrinos are called ghost particles.
Neutrino particles are produced in huge quantities in the interiors of stars, in quasars, during supernova explosions, during the decay of radioactive elements, and even during the interaction of cosmic rays with atoms of the upper layers of the earth's atmosphere. Also, neutrino particles, according to theories, should be produced in large enough quantities in accelerators such as the LHC, but their detection requires the installation of appropriate sensors and instruments.
And in 2018, the "correct" FASER instrument was installed next to the collider, designed specifically to detect neutrino particles. During the entire period of operation of the collider, the sensors of this instrument registered six cases of neutrino particles passing through them.
The equipment and sensors of the FASER instrument are located at a distance of 480 meters from the point of collision of the proton beams in the collider tunnel. The sensors consist of lead and tungsten plates, between which there is a layer of a special emulsion. When neutrino particles collide with atomic nuclei in plates of dense metal, a flow of secondary particles arises that move through the emulsion layer and leave characteristic traces. And for all the time, with the help of the emulsion, six corresponding neutrino tracks were recorded.
Having collected all the necessary information, the FASER experiment group is now preparing a new neutrino sensor, more massive and much more sensitive. This new sensor, FASERnu, will weigh 1,090 kilograms, in comparison, the first sensor weighs only 29 kilograms. A higher sensitivity will allow not only registering a larger number of particles, but also identifying the types of neutrinos and antineutrinos, which in science are called by the term "flavor".
Scientists expect that with the help of the new sensor they will be able to register about 10 thousand neutrino particles during the next period of the collider's operation, which will begin in 2022. “We hope that we will be able to catch the most high-energy neutrinos that were generated in the bowels of a man-made source, in other words, neutrino particles of artificial origin,” the researchers write.
The article was published in the journal Physical Review D
PHOTO: FASER experiment installed at the Large Hadron Collider to detect neutrinos from particle collisions © CERN

Certificate of registration of mass media ЭЛ № ФС 77 - 78868 issued by Roskomnadzor on 07.08.2020