Neutrinos (along with photons) are the most abundant particles in the universe. However, scientists do not know much about them. This is because these particles interact very weakly with matter and are extremely difficult to study. So faint that they are often referred to as “ghost particles”.
Neutrinos have an amazing penetrating ability. For example, a planet like Earth is almost no obstacle to them. Scientists estimate that 65 billion neutrinos pass through one square centimeter of our planet’s surface and hit the sun every second. These particles in large quantities and every second penetrate our bodies, and we usually have no idea about them.
The first speculation about the existence of neutrinos appeared in the 1930s, but the first experimental observations of them occurred almost a quarter of a century later. In the course of the research, it was discovered that there are at least three types of these particles – the electron, muon and tau neutrinos, and each of them has its counterpart in the world of antimatter, that is, each has its own antiparticle. These particles have no electrical charge and are produced in nuclear reactions inside stars as well as in reactors on Earth.
Although they are among the most abundant particles in the universe, observing them so far has proven challenging because the probability of them interacting with other matter is extremely low. To detect neutrinos, physicists use advanced detectors and equipment to study known neutrino sources. Their efforts eventually led to the detection of neutrinos from the sun, cosmic rays, supernovae and other cosmic bodies, as well as from nuclear reactors.
First observations at the LHC
Observing neutrinos inside particle accelerators such as the Large Hadron Collider has also been a longtime goal. Although physicists were confident that reactions that occur when particles accelerate to near the speed of light and collide with each other produce neutrinos, getting evidence for this was another matter entirely.
Now two large research teams – FASER (Forward Search Experiment) and SND (Scattering and Neutrino Detector)@LHC – have detected neutrinos for the first time using detectors at the Large Hadron Collider (LHC) at CERN in Switzerland. These observations may open important new experimental research opportunities in particle physics. The results of the observations have been published in two articles in Physical Review Letters (DOI: 10.1103/PhysRevLett.131.031801; DOI: 10.1103/PhysRevLett.131.031802).
“Neutrinos are produced in large quantities in proton colliders such as the LHC,” said Cristovao Vilela of the SND@LHC Collaboration. However, these neutrinos have not yet been directly observed. The very weak interaction of neutrinos with other particles makes them very difficult to detect, which is why they are the least studied particles in the Standard Model of particle physics, he added.
“Particle colliders have been around for more than 50 years and have discovered every known particle except neutrinos,” said Jonathan Lee Feng of the FASER Collaboration. – At the same time, every time neutrinos are discovered from a new source, be it a nuclear reactor, the sun, the Earth, or a supernova, we learn something very important about the universe. In our latest work, he added, we have detected for the first time the production of neutrinos in particle colliders.
The neutrinos discovered by Feng and his colleagues have the highest energy ever recorded in a laboratory setting. Thus, they could pave the way for in-depth studies of the properties of neutrinos, as well as a search for other elusive particles.
The work being carried out by the FASER and SND@LHC projects makes a significant contribution to ongoing experimental research in particle physics and may soon pave the way for further breakthroughs in this field. Now that the existence of neutrinos has been confirmed at the LHC, these two experiments will continue to collect data, which could lead to more useful observations and a better understanding of the nature of neutrinos.
“We will be using the FASER detector for many years and expect to collect at least ten times more data. A particularly interesting fact is that only a part of the detector was used in this initial detection. In the coming years, we will be able to use the full power of FASER to map A map of high-energy neutrino interactions in extremely detailed detail.
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