Groundbreaking CERN detector detects high-energy neutrinos for the first time

For the first time, researchers have directly observed high-energy interactions between electrons and muon neutrinos in the energy range of teraelectronvolts (TeV).

This milestone was achieved at CERN’s Large Hadron Collider (LHC) using the Forward Search Experiment (FASER).

Neutrinos are elementary particles with extremely small masses and weak interactions with matter. These “ghost particles” have fascinated physicists for a long time. Despite their frequency – countless neutrinos pass through the Earth and our bodies every second – their detection has proven difficult.

“This is the first physical result on neutrinos from a particle accelerator,” said Akitaka Ariga, an associate professor at Chiba University and one of the research leaders. He described the team’s efforts as “a breakthrough in particle physics that could revolutionize the strategy of large-scale experimental research in this field.”

A new look at the invisible

There are three “types” of neutrinos: electron neutrinos (ve), muon neutrinos (νμ), and tau neutrinos (ντ). To date, neutrino interaction cross sections have not been measured at energies above 300 gigaelectronvolts (GeV) for electron neutrinos and between 400 GeV and six teraelectronvolts (6000 GeV) for muon neutrinos.

At the heart of the new discovery is the FASERν detector, a special component of the FASER experiment at CERN. This detector consists of 730 layers of tungsten plates and emulsion films and has a total target mass of 1.1 tonnes. In addition, the FASERν is designed to reconstruct charged particle tracks resulting from neutrino interactions with submicron accuracy.

The team analyzed a subset of the exposed detector volume, corresponding to 128.6 kg, focusing on high-energy neutrinos produced by proton-proton collisions at the LHC.

Through rigorous selection, they identified four electron-neutrino and eight muon-neutrino interaction candidates, all with energies above 200 GeV.

In a statement, the team highlighted the high statistical significance of these observations – 5.2σ for electron neutrinos and 5.7σ for muon neutrinos. This indicates that these are most likely not background fluctuations and are therefore real neutrinos.

“These results demonstrate that it is possible to study interactions of taste-labeled neutrinos at TeV energies with the emulsion-based FASERν detector at the LHC,” emphasized Dr. Ariga.

Increase energy levels

The neutrinos detected are the most energetic neutrinos ever observed in an artificial source. Their energy is in the teraelectronvolt range.

Specifically, the study provides the first measurements of neutrino interaction cross sections – the probability that neutrinos interact with target particles – in the energy ranges of 560–1740 GeV for electron neutrinos and 520–1760 GeV for muon neutrinos.

These measurements fill a crucial gap, as previous studies did not extend beyond 300 GeV for electron neutrinos and 400 GeV to 6 TeV for muon neutrinos. Moreover, these measurements agreed with the predictions of the Standard Model.

The ability to study neutrinos at such extreme energies could shed light on fundamental questions in physics, such as why particles have mass and why there is more matter than antimatter in the universe.

Details of the team’s research were published in Physical Examination Letters on July 11, 2024.