During a test run of a new detector at the Large Hadron Collider (LHC)—the world’s biggest particle accelerator—the tiny “ghost particles” known as ‘neutrinos‘, were found. The detector is at CERN, which is near Geneva in Switzerland.

There have been no neutrinos found inside the LHC before. This is also the first time that they have been found inside any particle accelerator, which is why this is so important. The new discovery, published on Nov. 24, opens up a whole new way for scientists to study the world below the surface.

“Ghost particles” aren’t the only thing the scientists at the Forward Search Experiment (FASER) want to find. The team is also working on an experiment to look for “dark photons,” which physicists think could be linked to dark matter, the mysterious, non-luminous substance that is thought to make up about 85% of the universe’s matter.

It was made by CERN’s FASER. Before this, “prior to this project, no sign of neutrinos has ever been seen at a particle collider,” study co-author Jonathan Feng, a physics professor at the University of California, Irvine and co-leader of the FASER project, said in a statement.

“This significant breakthrough is a step toward developing a deeper understanding of these elusive particles and the role they play in the universe,” Feng said.

When you’re alive, about 100 billion neutrinos pass through each square centimeter of your body in a second. Those tiny particles can be found all over the place. They’re made in the nuclear fire of stars, huge supernova explosions, by cosmic rays, and radioactive decay, and they’re also made by particle accelerators and nuclear reactors on Earth.

But even though the particles are everywhere, it’s still hard to find them. It’s hard for neutrinos to interact with other types of matter because they don’t have an electric charge and have almost no mass.

True to their name, neutrinos think of the universe’s normal matter as intangible, and they move through it at a speed close to the speed of light, just like ghosts do.

However, just because neutrinos are hard to catch doesn’t mean that they can’t be caught at all. There is an effect called Cherenkov radiation that some of the most well-known neutrino detectors have used to detect solar-generated neutrinos. This is how these detectors have found them.

A particle traveling through a light-slowing material (like water) faster than light is able to generate a faint blue glow in its wake, just like a jet traveling faster than the speed of sound does. When neutrinos hit an atomic nucleus squarely, they produce a light that allows scientists to see the particle byproducts that result.

There are still a lot of things that scientists don’t know about how high-energy neutrinos are made when particles smash together inside particle accelerators, though. The scientists at the FASER collaboration came up with a new detector called the FASERnu in order to look for these home-made ones.

You can think of it as a “emulsion-wrapped” cookie that can detect small particles. It has dense metal plates of lead and tungsten that are sandwiched between layers of “emulsion.” In the first place, the neutrinos smash into the atomic nuclei in the dense metal plates to make the particles they leave behind.

When the neutrino byproducts hit the emulsion layers, they react with them and leave behind the traced outlines of the particles as they zip through them. This is how Feng says this works.

By “developing” the emulsion and looking at the particle trails left behind, the physicists were able to figure out that some of the marks were made by neutrinos. They could even figure out which of the three types of neutrinos they had found. This means that not only did they pick the right place inside the huge 17-mile (27-kilometer) ring to look for neutrinos, but their new detector was also able to see them.

After they found a detector that worked, the scientists are now building a bigger version of it, which they say will be even better at spotting neutrinos and their antimatter counterparts, called antineutrinos. They say it will also be able to tell the difference between neutrinos and their antimatter counterparts.

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