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Second Largest Man-Made Structure to Look Through Earth at Astrophysical Neutrinos


So by looking at them, we can probe the far and violent universe.”

KM3NeT concept design. (Image: KM3NeT Consortium via Popular Science)

Most people had never heard of a neutrino until Italian researchers earlier this year, claimed they had observed the elementary sub-atomic particle as traveling faster than the speed of light -- a discovery that has yet to be verified under peer review. In this case, the neutrinos were created in a beam of protons by a particle accelerator, but neutrinos are created in other ways including violent, deep space events that smash atomic particles and could send astrophysical neutrinos toward Earth.

These are the neutrinos that European scientists hope to see. But finding them is exceedingly difficult. So, the researchers are setting out to build the second largest man-made structure under the Mediterranean Sea to watch for them.

Popular Science has more on what the researchers hope to gain from technology that would look through the earth -- yes, through the Earth -- and would be second only to the Great Wall of China in size:

Nestled beneath 3,200 feet of Mediterranean seawater, a neutrino detector called KM3NeT will stare at the seafloor in an effort to see neutrinos making their way through the Earth. The detector, spanning three cubic kilometers, will also serve as a new oceanography observatory in one of the world’s busiest bodies of water, helping biologists listen to whales and study bioluminescent organisms. It will be the largest structure ever made by humans after the Great Wall of China, said physicist Giorgio Riccobene, a staff researcher at the National Institute for Nuclear Physics who is working on the project. “The problem will be that nobody will see that,” he said with a laugh.

The goal is to find astrophysical neutrinos originating in cosmic cataclysms, Riccobene said. They could help explain the origin of cosmic rays, the proton flux that rains down on the Earth from unknown sources. To get past the magnetic fields provided by our galaxy, sun, and Earth itself, these cosmic rays must be incredibly powerful, but cosmic rays don’t point back to their sources the way light would. Neutrinos can help reconstruct their paths.

“At these energies,” Riccobene said, “the only high energy particles that can come from very distant sources are neutrinos. So by looking at them, we can probe the far and violent universe.”

Popular Science reports that the first phase of the $27.7 million project is being conducted in collaboration of 40 research institutions from 10 European countries. The first stage of KM3NeT will be composed of 30 towers and 37,200 photomultiplier modules, which are reported to "catch the telltale flashes" of a neutrino.

Since neutrinos are, like their name, little and neutral in charge, they can pass through almost anything. The researchers are setting up shop in the ocean to use it as an "underwater telescope" to see the interaction of neutrinos with other charged particles clearly. And, by looking through Earth, the scientists hope to rule out that they may be seeing atmospheric neutrinos instead of the astrophysical neutrinos, which are the ones they are seeking.

What researchers will be looking for, Popular Science reports, are blue flashes that occur when neutrinos may interact with charged particles:

Think of it like a game of billiards, explains Riccobene.

“The neutrino is the shot that breaks the ‘castle,’ the group of billiard balls that form the nucleus of an atom. When it breaks this castle, there is a possibility that an outgoing particle can be produced,” he said. If it is a muon — a charged subatomic bit, a much larger cousin to the electron — this is good news. The muon formation radiates a cone of blue light, known as Cherenkov radiation. If physicists are lucky, that flash will happen in a clear and deep medium, like Antarctic ice or the depths of the Mediterranean.

The photomultiplier tubes mentioned earlier will be able to detect such flashes, but the researchers have improved upon previous technology of the tubes to increase "resolution and tracking." As for the towers on which the the photomultiplier tubes will be placed on, Popular Science states they  will be about 2,624 feet tall.

Popular Science reports that some don't agree with the project's bigger-is-better stance to finding neutrinos:

“There’s a segment of the physics community who make the argument, these are particles with a higher energy you could ever hope to produce in an accelerator, which is true. And they may tell us something different about the cosmos, that’s true. But it’s all ‘could be.’ And I haven’t seen anything from any of these experiments that tells us anything that’s new,” said [Peter Fisher, a particle physicist at the Massachusetts Institute of Technology.] “The way I’d look at it is, if you saw something, if there was some interesting new particle produced at the Large Hadron Collider, and you knew something about its properties, then you would know what to look for and what kind of detector to build. But just building bigger and bigger hasn’t worked so far.”

Popular Science states that the photomultiplier tubes are already being built and tested, and construction on the KM3NeT as a whole is expected to begin sometime next year.

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