'With this ultra-high energy neutrino, we are opening a new window in our universe.'
Of all the fundamental particles that make up the standard model of particle physics, neutrinos remain the most enigmatic. They're virtually weightless—but not quite! They carry no electric charge and almost never interact with other particles. They don't even seem to have a fixed identity, instead oscillating constantly between their three different "flavors." They're streaming through your body as you read this—the sun is constantly producing colossal quantities of them—but detecting them remains difficult, and there's still a great deal we don't know about them. "Neutrinos are very mysterious particles," says Damien Dornic, one of the co-authors of a new paper published February 12 in Nature that describes the detection of the decay products of an extremely high energy neutrino by the Kilometer Cubed Neutrino Telescope (KM3NeT), a neutrino detector located deep beneath the Mediterranean Sea. Scientists calculate that the neutrino carried an energy of around 220 peta-electronvolts (PeV), making it the single most energetic neutrino ever observed. (220 PeV is an extraordinarily high energy: for comparison, the Large Hadron Collider collides particles at a maximum energy of 13.6 tera-electronvolts, which is just 0.006% of the neutrino's estimated energy; conversely, this means that the neutrino carried the energy of over 16,000 LHC collisions.) The neutrino itself was not observed directly; rather, its existence was implied from the detection of another particle called a muon, which lit up one of the two particle detectors on February 13, 2023. Scientists have spent the last two years examining the data and reconstructing the trajectory of the muon, concluding that it was created by the interaction between a matter particle and the ultra-high energy…