They’ve discovered the most energetic neutrino in history, but its discoverer won’t say where it came from.

These ultra-high-energy neutrinos, tiny particles that travel almost at the speed of light, were not known until about a decade ago, and scientists believe they are “messengers” carrying information about some of the world’s most catastrophic events. violent events in the Universe, such as the merger of huge black holes in very distant galaxies.

For this reason, the intervention of physicist Joao Coelho from the Laboratory of Astroparticles and Cosmology in Paris surprised everyone on June 18 during the Neutrino 24 conference held in Milan. Because it is this neutrino, according to Coelho, that “stands out much higher than all the others.”

However, perhaps in order not to alert possible competitors, the researcher did not want to reveal either the exact origin of the unusual particle or the moment at which the observation occurred, but promised that these and other details would be revealed “soon.” in a future article.

Forest of ropes at the bottom of the sea

ARCA is the largest component of a neutrino observatory called the Kubic Kilometer Neutrino Telescope (KM3NeT), which also includes a detector array in Toulon, France, and is being built in collaboration with European countries along with Morocco, South Africa. Australia, Georgia, China and the United Arab Emirates.

ARCA, which currently consists of 28 “ropes,” has been collecting data since the mid-2010s, although the planned plan calls for the number to reach 230 by 2028. Each rope is 800 meters long and “bedecked” with 18 detectors. units, half of which consist of meter-wide plexiglass spheres filled with “light detectors”, each of which can only detect a few photons.

Most of the light detected by ARCA comes from high-energy cosmic ray particles that, when they hit Earth’s atmosphere, create cascades of other electrically charged subatomic particles. These “showers” can travel miles across the water and leave behind faint flashes of light that ARCA is designed to detect.

But the observatory can also detect light from other types of particles, including neutrinos. That is, he “sees” not neutrinos directly, but the particles they produce when they collide with a molecule (air, water or stone). These secondary particles, called muons, in turn create a stream of other charged particles as they pass through the detector. Neutrinos are so light that they can cross planets like Earth from side to side as if they did not exist, so the showers of particles they produce in their few collisions can come from any direction, even from Earth, while as cascades of particles that are formed from cosmic rays, usually emanating from the atmosphere. So when ARCA detects a shower coming from above, it can be difficult to determine whether the source is a neutrino or not, but showers that are horizontal or “coming from below” are much more likely.

However, the Earth itself acts as a kind of barrier for the most energetic neutrinos, having an energy of half a petaelectronvolt or more (an electronvolt is the energy acquired by an electron when crossing a potential difference of one volt in a vacuum), which leaves a strip of sky around the horizon where particles in contact with the Earth , are easier to detect and distinguish from cosmic rays. And it is there, in that narrow region, that it is easiest to observe these ultra-high energy neutrinos.

Ten times more powerful

During his talk, Coelho said that during his observations, more than a third of ARCA’s sensors detected flashes consistent with a muon crossing the observatory horizontally, caused by a neutrino arriving about one degree below the horizon. According to the researcher, the particle had enormous energy, amounting to many tens of petaelectronvolts, which had never been observed before and making it by far the most energetic one ever discovered.

But what cosmic event could create particles with such energy? Is this some known process or something even more cruel that no one has ever seen? Due to the lack of additional data, this is impossible to know. The only thing that can be done for now is to wait for Coelho’s decision to publish his article with all the details.