A Particle Detector, ANITA, Has Spotted A New Particle

Antarctic Impulsive Transient Antenna or ANITA is a particle detector. A team of physicists at Antarctica use Antarctic Impulsive Transient Antenna to search high-energy particles from space. ANITA floats on a helium balloon at an altitude of 37 kilometres for about a month at a time and collects radio waves. The way it works is simple. When high-energy particles from space, including lightweight, ghostly particles called neutrinos, interact Antarctica’s ice, which produces radio waves. That radiowaves are picked up by ANITA’s antennas. Now all physicists have to do is look for its frequency, wavelength and all those data to tell which particles radio wave it is.

September 2018 ANITA spotted two unusual signals something that standard physics is at a loss to explain. A team of physicists at Penn State report about this online on September 25 at arXiv.org/abs/1809.09615. The result of that findings hints at the possibility of new particles beyond those catalogued in the standard model, the theory that describes the various elementary particles that make up the matter. We can say that these weird particles from space may defy physicists’ standard model. Now Particle Physicists might be going to modify the standard model or they might have to come up with new.

The two puzzling signals appear to be from extremely energetic neutrinos shooting skyward from within the Earth. A neutrino coming up from below isn’t inherently surprising: Low-energy neutrinos interact with matter so weakly that they can zip through the entire planet. But high-energy neutrinos can’t pass through as much material as lower-energy neutrinos can. So although high-energy neutrinos can skim the edges of the planet, they won’t survive a pass straight through.

The steep angle of the particles’ paths suggests that the neutrinos travelled through several thousands of kilometres of Earth too much for a high-energy neutrino to make it out the other side. That’s according to computer simulations in the new study, by researchers who are not members of the ANITA collaboration. ANITA researchers have been looking for a way to explain the signals with neutrinos, says Derek Fox, a co-author of the study. But according to Fox and colleagues’ simulations, “those attempts must fail.”

A high-energy particle could make such a long trek through the Earth only if it were even more reticent to interact with matter than neutrinos are. A hypothetical heavy particle called a stau, proposed in a theory called supersymmetry could fit the bill, Fox and colleagues say. After being created on the other side of the planet by a high-energy neutrino slamming into the Earth, a stau could make it through unscathed before decaying into lighter particles that would eventually result in the signals detected by ANITA.

“It’s still possible that there is a very mundane reason that we are seeing these events in ANITA,” says ANITA physicist Stephanie Wissel of Cal Poly in San Luis Obispo, Calif. Other spacefaring particles called cosmic rays, which rain down from above, produce similar signatures in ANITA. A basic misunderstanding of the physics behind cosmic rays’ signatures could explain the observations, Wissel says.

Backing up their claim, Fox and colleagues also identify three events in another Antarctic neutrino detector that they say have some similarly puzzling properties. But the leader of that experiment, physicist Francis Halzen of the University of Wisconsin–Madison, isn’t convinced. “These events are of course worth paying attention to,” he says, but he doesn’t see any evidence that they require a new explanation.

What’s needed is more data, physicists say. The ANITA team plans to send the detector up for another Antarctic balloon ride, says ANITA physicist Amy Connolly of Ohio State University in Columbus. “My view is that we should keep trying to find a mundane explanation for these events.”

The standard model has been confirmed time and time again, so physicists are loathe to abandon it without overwhelming evidence. “The case that ANITA is seeing something weird is strong,” says astrophysicist John Beacom, also of Ohio State. But “I always bet for the standard model.”

Still, these events have such extreme energies that they are reaching into realms not accessible at particle colliders like the Large Hadron Collider near Geneva, Beacom says. “There’s a lot we just don’t know about how physics works at these high energies.”

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