Two unusual signals were picked up by a detector suspended from a balloon above Antarctica
Science News said:Dangling from a balloon high above Antarctica, a particle detector has spotted something that standard physics is at a loss to explain.
Two unusual signals seen by the detector, known as the Antarctic Impulsive Transient Antenna, or ANITA, can’t be attributed to any known particles, a team of physicists at Penn State reports online September 25 at arXiv.org. The result hints at the possibility of new particles beyond those cataloged in the standard model, the theory that describes the various elementary particles that make up matter.
Like the old man in the Pixar movie Up, ANITA floats on a helium balloon, at an altitude of 37 kilometers for about a month at a time. It searches for the signals of high-energy particles from space, including lightweight, ghostly particles called neutrinos. Those neutrinos can interact within Antarctica’s ice, producing radio waves that are picked up by ANITA’s antennas.
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 traveled through several thousands of kilometers 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 coauthor 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 (SN: 10/1/16, p. 12), 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.
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