It was over almost as soon as it started, but the momentary flicker was all physicists needed to make the call. The muon collision their detectors picked up was a byproduct of a powerful subatomic collision, one that involved the most energetic neutrino yet discovered.
The muon interaction was captured by the IceCube Neutrino Observatory, a 3.5-billion-cubic-foot patch of Antarctic ice that physicists have woven with photomultiplier tubes built to capture one of the rarest events in the subatomic world—a neutrino interacting with matter. While in this case they didn’t witness the superfast neutrino zipping through the ice, they were able to use the data gleaned from the muon to determine the speed and energy of the source neutrino when it had slammed into another particle.
Physicists have been closely observing the Antarctic ice since 2013, and they’ve seen evidence of more than 50 neutrinos since then.
Neutrinos are particles with vanishingly small mass that fly through the universe, often passing unhindered through stars, planets, and people. They’re produced by a number of spectacular astronomical phenomena, from black holes and neutron stars to gamma-ray bursts. When neutrinos do interact with particles that have greater mass, they emit a brief flash of light or, in the case of a direct collision, throw off another subatomic particle. These brief encounters can fill scientists in on the phenomena that produced the neutrino or the details of neutrinos themselves.
The latest neutrino data from the IceCube team suggests the subatomic particle was the fastest ever discovered and far more powerful than the beam in the Large Hadron Collider. Here’s Jonathan Webb, reporting for BBC News:
By doing what [IceCube collaborator Francis] Halzen calls “back of an envelope” physics calculations, his team can reconstruct the neutrino interaction that spat the muon into the ice, where it dumped those 2,600 TeV.
“It was made by a neutrino that came through the Earth somewhere below our detector,” said IceCube’s principal investigator Francis Halzen, of the University of Wisconsin-Madison.
For a slippery, near-massless particle, this neutrino packed a punch.
“Using standard model physics, the energy of this neutrino is somewhere around 5,000-10,000 TeV, with the most likely value somewhere in the middle,” Prof Halzen explained.
“This neutrino packs about 1,000 times the energy of the LHC beam. It is spectacular.”
At another experiment on the other side of the Earth, physicists spotted a geo-neutrino, or one that originated in the intense heat, pressure, and radioactivity generated by our our planet’s mantle and core. The particle was caught by photomultiplier tubes in the Borexino experiment, which is based in Italy and is focused on a giant spherical cavern filled with a mix of 1,2,4-trimethylbenzene and 2,5-diphenyloxazole, organic compounds that throw off scintillation light when they interact with neutrinos.
Borexino scientists hope that data from the neutrinos will help them understand the nature of radioactivity deep in the Earth.
Photo credit: Penn State/Flickr (CC BY-NC-ND)