SND@LHC published the first observation of neutrinos produced in particle collisions at an accelerator
"The SND@LHC and FASER collaborations just published in Physical Review Letters their first results, from which emerges the first observation of high-energy muonic neutrinos produced at the LHC. SND@LHC has a strong involvement of LIP, who led the data analysis."
The results, published and highlighted as "Editor's Suggestion" in the scientific journal Physical Review Letters, are based on data accumulated between July and November 2022, and correspond to the first direct observation of neutrinos produced at the LHC. The Physics Magazine of the American Physical Society dedicated a "Viewpoint" article to the observation.
The analysis of the SND@LHC data, led by the LIP group, involved a major rejection of noise events and revealed the presence of neutrino interaction events with a statistical significance above 5 sigma.
SND@LHC is a new experiment at CERN that aims to extend the LHC potential to the study of neutrinos. It was designed to detect and study the three types (flavours) of neutrinos (and potential new weakly interacting particles) that are produced at the LHC. LIP has been involved in the project since its inception and has made important contributions to the construction of the detector, namely the muon detection system.
Neutrinos are among the most abundant elementary particles in the Universe but rarely interact with matter. For this reason, they are particularly difficult to detect and are not observed by the typical collider experiment detectors, where their presence can only be inferred from the missing energy.
The detection of neutrinos in SND@LHC is done through the particles that result from their interaction with the matter constituting the detector. Specifically, the presence of a muonic neutrino is revealed by the detection of a muon among the products of the interaction. The muon in turn traverses the entire length of the detector, leaving a clear signature.
However, not all muons that pass through the detector come from a neutrino interaction. "The main challenge overcome in this work is the background noise caused by high-energy muons from proton-proton collisions," says Cristóvão Vilela, the LIP researcher who led the data analysis. "These particles pass through the detector with a frequency a hundred million times higher than that of neutrino interactions, and their interactions with the matter surrounding the detector produce neutral hadrons whose signals in the detector resemble those of neutrinos."
The measurement represents a major technological success, confirming the ability of the detection system adopted by SND@LHC to identify such rare interactions. But observing the first neutrinos at the LHC is only a first step. "With this first result we have inaugurated a new era: that of neutrino physics at colliders", says Nuno Leonardo, who coordinates the LIP group at SND@LHC. "The data we continue to accumulate at the LHC will allow us to advance the study of the muon neutrino with higher statistics as well as the detection of electron and tau neutrinos." This opens up, also at LIP, a "new line of research into the properties of these elusive particles and a new door to test fundamental interactions".
The LIP team in the SND@LHC experiment counts also on the participation of Alberto Blanco, Paula Bordalo, Tiziano Camporesi, Paulo Fonte, Luís Lopes, Sérgio Ramos, João Saraiva and Guilherme Soares.
Figures from the article now published: schematic representation of the detector; muon neutrino interaction candidate event (see article for more information).
