The ghost particles, it turns out, have stories to tell.
For decades, physicists suspected the Large Hadron Collider was producing neutrinos — particles so ghostly they pass through entire planets without a trace — yet no one had ever caught one there. In November 2021, a team from UC Irvine changed that, detecting six neutrino interactions buried 480 meters beneath the collider using little more than metal plates and photographic emulsion. It is a small number that carries enormous weight: proof that the universe's most elusive messengers can be intercepted, and that the information they carry — pristine records of supernovae, quasars, and the deep structure of reality — may finally be within reach.
- Neutrinos have evaded every previous attempt at detection inside a particle collider, slipping through matter so effortlessly that trillions pass through the human body every second unnoticed.
- The FASER experiment, quietly installed in 2018, placed itself directly in the neutrinos' path — a stack of lead, tungsten, and photographic emulsion waiting for the rarest of collisions to leave a mark.
- Six faint tracks appeared in the emulsion after chemical processing, each one a ghost particle caught mid-flight — modest in number, but historic in meaning.
- The detection confirmed the method works, and the team is already building FASERnu, a detector seventeen times heavier, poised to capture over 10,000 interactions when the LHC restarts in 2022.
- What began as a proof of concept is becoming a precision instrument — one that could turn neutrinos from cosmic curiosities into windows onto the most violent events in the universe.
For decades, physicists knew the Large Hadron Collider must be producing neutrinos — but knowing and catching are two different things. In November 2021, a team from UC Irvine announced they had finally done it: six neutrino interactions detected inside the LHC itself, captured by a detector positioned 480 meters beneath the collision chamber.
Neutrinos are among the strangest objects in physics. Nearly massless and electrically neutral, they interact so weakly with matter that trillions pass through your body every second without effect. Yet this very elusiveness makes them valuable — unlike light, which bends and scatters across space, neutrinos travel unaltered from their sources, carrying untouched information from supernovae, quasars, and the cores of stars.
The FASER experiment used a disarmingly simple approach: place a detector directly in the neutrinos' path, layered with lead and tungsten plates separated by photographic emulsion. On the rare occasion a neutrino struck a nucleus, secondary particles left visible tracks in the emulsion — revealed only after chemical development, like old film brought to light. Six such tracks appeared. It was enough.
Lead author Jonathan Feng called it a significant breakthrough — the first time any particle collider had ever detected neutrinos. The result, published in Physical Review D, validated both the detector and the method. The team is now building FASERnu, seventeen times heavier than the original, expected to record more than 10,000 interactions when the LHC restarts in 2022. The ghost particles, it turns out, have been waiting all along to tell their stories.
For decades, physicists have known that the Large Hadron Collider should be producing neutrinos—those ghostly, nearly massless particles that stream through the universe by the trillions without leaving a trace. But knowing something should happen and actually catching it are two different things. In November 2021, a team from the University of California, Irvine announced they had done what no one had managed before: they had detected neutrinos at the LHC itself, capturing six distinct interactions in a detector buried 480 meters beneath the collision chamber.
Neutrinos earned their nickname for good reason. They carry almost no mass, possess no electric charge, and interact so weakly with ordinary matter that trillions pass through your body every second without you noticing. A neutrino can travel across the entire universe and never bump into anything. This makes them extraordinarily difficult to catch—but also extraordinarily valuable. Unlike photons, which get bent and scattered as they travel through space, neutrinos arrive pristine and unaltered, carrying information from the most violent and distant events in the cosmos: supernovae, quasars, the hearts of stars.
The FASER experiment, installed in 2018, took a straightforward approach to the detection problem. Physicists positioned an instrument directly in the path of neutrinos produced by particle collisions, then lined it with plates of lead and tungsten separated by layers of photographic emulsion. When a neutrino occasionally collided with a nucleus in the metal, it produced secondary particles that left visible tracks in the emulsion—marks that became apparent only after chemical processing, much like developing old film. During the initial run, six such marks appeared. It was a small number, but it was proof.
Jonathan Feng, one of the study's authors, called the detection "a significant breakthrough," noting that no particle collider had ever captured neutrinos before. The finding, published in Physical Review D, opened a door that had remained closed. It meant the detector worked. It meant the method was sound. It meant the next step was possible.
That next step is already underway. The team is building FASERnu, an upgraded detector roughly 17 times heavier than the original—2,400 pounds compared to 64 pounds—with substantially greater sensitivity. When the LHC restarts in 2022, Feng and his colleagues expect FASERnu to record more than 10,000 neutrino interactions. That volume of data will transform neutrinos from a curiosity into a tool, allowing physicists to study these particles in ways that were impossible before and to understand their role in the fundamental structure of reality. The ghost particles, it turns out, have stories to tell.
Citas Notables
Prior to this project, no sign of neutrinos has ever been seen at a particle collider. This significant breakthrough is a step toward developing a deeper understanding of these elusive particles and the role they play in the universe.— Jonathan Feng, study co-author, University of California, Irvine
The UCI team expects FASERnu to record more than 10,000 neutrino interactions in the next run of the LHC, beginning in 2022.— David Casper, study co-author
La Conversación del Hearth Otra perspectiva de la historia
Why does it matter that we detected neutrinos at the LHC specifically? Aren't they everywhere?
They are everywhere, yes—but we've never caught them being made in a controlled setting before. The LHC lets us know exactly when and where the collision happens, so we can study the neutrinos it produces under laboratory conditions. That's the difference between seeing something and understanding it.
And the fact that they don't interact with matter—that's actually an advantage?
Completely. Light gets scattered and absorbed as it travels through space, so by the time it reaches us, it's been altered. Neutrinos pass through everything untouched. They're like messengers that never get interrupted.
Six interactions seems like a very small number. Why is that enough to call it a breakthrough?
Because it's six more than anyone had ever found before. It proves the detector works, that the method is sound. Now they can build a bigger one and collect thousands more. You have to find the first one before you can find the rest.
What will they actually learn from 10,000 neutrino interactions?
That's the open question. They'll be able to study how neutrinos behave, what they tell us about the collisions that made them, and eventually how to use them as a window into cosmic events we can't see any other way.
So this is really just the beginning.
Exactly. This is the proof of concept. The real work starts when FASERnu comes online.