Record-breaking neutrino spotted deep in the Mediterranean sea

Scientists recently shared news of a particle event that has sparked excitement in the physics community. One of the most energetic neutrinos ever recorded was observed in the Mediterranean Sea by the ARCA detector of the KM3NeT project.

The astounding neutrino, named KM3-230213A, has caught global attention. Researchers estimate its energy at about 220 million billion.

“KM3NeT has begun to probe a range of energy and sensitivity where detected neutrinos may originate from extreme astrophysical phenomena,“ said Paschal Coyle, a researcher at the National Centre for Scientific Research (CNRS).

“This first ever detection of a neutrino of hundreds of PeV opens a new chapter in neutrino astronomy and a new observational window on the Universe.”

Mysterious elementary particles

Neutrinos travel across the universe, slipping through stars and planets without much disturbance.

For decades, scientists have aimed to spot ultra-high-energy neutrinos to shed light on cosmic accelerators. The KM3NeT Collaboration unites more than 360 experts from 68 institutions in 21 countries.

“Neutrinos are one of the most mysterious of elementary particles. They have no electric charge, almost no mass and interact only weakly with matter. They are special cosmic messengers,” said Rosa Coniglione, a researcher at the INFN National Institute for Nuclear Physics.

How deep-sea sensors detect neutrinos

KM3NeT is a sprawling setup resting on the seabed, composed of two detectors called ARCA and ORCA.

ARCA is located about 50 miles from Portopalo di Capo Passero, Sicily, at a depth of 11,319 feet. ORCA is positioned near Toulon, France, at a depth of 8,038 feet.

Each site serves a distinct goal, with ARCA tuned for high-energy neutrinos and ORCA for lower-energy neutrinos.

The detectors depend on photomultipliers nestled within glass spheres. When a cosmic neutrino collides with water molecules, faint bluish light appears. The sensors collect that light, letting researchers map the neutrino’s journey.

Remarkable single muon

ARCA picked up a single muon, which signaled a neutrino interaction close by. Its path across the detector left a trail that triggered a large number of active sensors.

This confirmed the neutrino was cosmic in origin rather than coming from local backgrounds.

“To determine the direction and energy of this neutrino required a precise calibration of the telescope and sophisticated track reconstruction algorithms,” said Aart Heijboer, KM3NeT Physics and Software Manager.

Origins of high-energy neutrinos

Scientists suggest that such high-energy neutrinos could come from cataclysmic sources like supernova remnants or supermassive black holes.

Interactions between cosmic rays and other matter or photons can also create these neutrinos. Some of the most energetic cosmic rays in the universe may bump into the cosmic microwave background, producing what researchers call “cosmogenic” neutrinos.

Studying these events may unmask fresh secrets of the universe, offering a direct clue about the places and processes that fling particles to unimaginable energies.

As these neutrinos fly mostly unimpeded from their source, they can deliver information that light or charged particles cannot.

Advancing neutrino astronomy

The ARCA site will eventually include 230 detection units, while the ORCA site will have 115. Each unit features 18 high-tech optical modules, and altogether, KM3NeT will span over a cubic kilometer of water. 

Miles Lindsey Clark is the KM3NeT Technical Project Manager and research engineer at the CNRS – Astroparticle and Cosmology laboratory in France.

“The scale of KM3NeT, eventually encompassing a volume of about one cubic kilometer with a total of about 200 000 photomultipliers, along with its extreme location in the abyss of the Mediterranean Sea, demonstrates the extraordinary efforts required to advance neutrino astronomy and particle physics,” said Clark.

Capturing a rare event

Though the installation is incomplete, ARCA was able to catch one of the rarest events in nature. With advanced calibration and data analysis, teams extracted the trajectory and energy details of this neutrino.

Since it most likely entered the water with more than 220 PeV of energy, that single neutrino opens the door to more surprises as KM3NeT continues to grow.

Such an event supports the existence of even higher-energy cosmic neutrinos. Different from lower-energy detections, these ultra-high-energy signals hint that distinct astrophysical engines could drive them.

Future research directions

Teams worldwide aim to see if this was a “cosmogenic” neutrino or if it sprang from an active celestial powerhouse.

Eventually, a bigger fleet of detection units will allow more frequent captures of such signals, improving the odds of pinpointing their origin and clarifying the forces that shape our universe.

“We stand at a frontier where new data will sharpen our understanding of the cosmos,” said a KM3NeT representative. Each new detection offers a chance to spot patterns and compare them with signals from gamma-ray telescopes and other observatories.

The study is published in the journal Nature.

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