For the first time, scientists have detected neutrinos produced by proton collisions at CERN’s Large Hadron Collider. This was done during the FASER experiment, in which Russian scientists take part. How important is the achievement and what it will bring to the study of space, a member of the collaboration, a researcher at the Joint Institute for Nuclear Research (Dubna) Svetlana Vasina, told RTVI.
Svetlana Vasina is a researcher at the Joint Institute for Nuclear Research (JINR), Scientific and Experimental Department of Elementary Particle Physics, Laboratory of Nuclear Problems.
Works in DsTau/NA65, FASER experiments. At DsTau/NA65 (CERN), responsible for data modeling, involved in data analysis, member of the executive committee of the experiment. FASER is also involved in modeling the response of emulsion detectors.
Participates in the study of natural and archaeological objects using the method of muon radiography using photoemulsion detectors. In addition to data analysis, he is involved in the manufacture of photoemulsion detectors, development and data collection using automatic scanning stations.
Your colleagues from the FASER experiment at CERN’s Large Hadron Collider have reported the first-ever detection of neutrinos produced at the accelerator. However, in 2011, the whole world was discussing the recording in the Italian experiment OPERA of neutrinos born at CERN, which would have moved at superluminal speed. What is the difference between these and current neutrinos?
The message speaks of the recording not only of neutrinos from accelerators. Physicists have been working with beams of such neutrinos for a long time, for example, 40 years ago such a beam was at the Protvino accelerator. Now, for the first time, neutrinos have been recorded from the Large Hadron Collider, where protons with an energy of 7 TeV collide. Accordingly, the neutrinos that are born in this case, among other particles, have an ultra-high energy of several hundred GeV to 2-3 TeV.
The FASER experiment detects neutrinos emitted in a very narrow cone from the beam intersection point in the ATLAS detector, which itself cannot see them.
By the way, another goal of the FASER experiment is to search for exotic particles that can also be produced at the LHC in an angular range inaccessible to the ATLAS detector. In particular, they are looking for so-called dark photons, candidates for the role of elements of dark matter – the main mystery for physicists today.
The FASER facility uses a nuclear emulsion detector to detect neutrinos. With the help of modern and highly efficient automatic tools and methods, the information on the traces of particles recorded in the emulsion is extracted and analyzed. Thanks to the high resolution, we can identify all types of neutrinos – electrons, muons and tau neutrinos. But still, the analysis of emulsion detector data requires much more time. Previously, FASER had already reported the first LHC neutrinos recorded in the emulsion detector, but the statistics for these events were still low. However, the electronic detectors, which are used in the FASER facility to search for exotic particles, also see the products of neutrino interaction with the emulsion detector. An analysis of the data from these detectors yielded a new result.
When were neutrinos detected?
The data was collected during the entire session of the previous year. At the initial stage of the analysis of electron detector data, only muon neutrino interactions were selected and 153 events were found. Considering all the background processes that can mimic neutrino interactions, the result has very high statistical significance – 16 sigma in physicist lingo. (A finding is considered a result with statistical significance greater than 5 sigma.)
You are three, employees of JINR, in the collaboration. What is your role?
Yes, we are three physicists and another engineer. We all come from other neutrino experiments and have experience with emulsion and electron detectors. We participate in the preparation of the detector for the collection of data, the simulation of the experiment, the analysis of the data obtained. In general, FASER is a small experiment – about 80 participants from 22 institutes, so all groups are small.
What is the fundamental significance of this discovery?
Strictly speaking, it’s not quite a discovery. The fact that neutrinos are produced at the collider is well known. However, no one has yet been able to register them; special detectors and experimental approaches were needed. The undeniable novelty of the announced result is that the work is now starting with neutrinos in a whole new energy range, inaccessible until now. The result shows that we can indeed record these neutrinos, work with them and further study their properties, in particular the cross section of their interaction with matter. This is important because, until now, physicists had data on neutrinos of much lower energies (from the sun, from reactors, even neutrinos from accelerators only have energies down to several tens of GeV) , or on much higher energy neutrinos from space. The latter are recorded using giant detectors up to one cubic kilometer in volume, one of which, the Baikal-GVD, is successfully working in our country.
Measuring the interaction cross section and other properties of collider neutrinos will help clarify the properties of neutrinos reaching us from distant objects in the Universe, and ultimately help understand their origin.
What are the prospects for discovering possible carriers of dark matter with your detector?
We do not know today what the so-called dark matter consists of. Its existence stems from observed gravitational phenomena, interpreted using Einstein’s theory. To date, several models offer an explanation for this phenomenon, including those that predict the birth of dark matter particles at the collider. One of the candidates for such particles is the so-called dark photon, it has a clear decay topology, it is more or less clear how to register it.
In experiments where they are looking for dark matter, and there is a lot of it, nothing has been recorded yet. However, even a negative result, as you know, is also useful and can be important. Failure to observe the particles or phenomena predicted by the models allows these theories to be refined or discarded altogether, setting limits on the likelihood of their existence.
