• Physicists at the Institute for Nuclear Research in Debrecen, Hungary used this electron-positron spectrometer to find evidence for a new particle that might be the fifth fundamental force of nature.

Physicists at the Institute for Nuclear Research in Debrecen, Hungary used this electron-positron spectrometer to find evidence for a new particle that might be the fifth fundamental force of nature. (Photo : Institute for Nuclear Reserch, Hungary)

Two teams of scientists from Hungary and the United States have announced what they say is the fifth fundamental force of nature, a revolutionary discovery that, if verified by other experiments, will change our basic understanding of the universe.

A new study by scientists at the University of California, Irvine confirms a finding in 2012 by a team of experimental nuclear physicists at the Institute for Nuclear Research in Debrecen, Hungary, who reported an anomaly or "bump" they discovered in radioactive decay of the unstable beryllium-8 nuclei could be the signature of a previously unknown fifth fundamental force of nature.

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The Hungarians had discovered a new particle they calculated has a mass of some 17 megaelectronvolts (MeV) that then decays into an electron-positron pair. They first believed this bump to be a "dark photon," a hypothetical elementary particle proposed as an electromagnetic force carrier for dark matter.

Attila Krasznahorkay at the Hungarian Academy of Sciences' Institute for Nuclear Research in Debrecen and his colleagues reported their surprising result in 2015 on the arXiv preprint server. They also detailed their findings last January in the journal Physical Review Letters.

"If true, it's revolutionary," said study author Jonathan Feng, a professor of physics and astronomy at UC- Irvine who was part of the American team that confirmed the Hungarian's findings.

"For decades, we've known of four fundamental forces: gravitation, electromagnetism, and the strong and weak nuclear forces," he noted.

"If confirmed by further experiments, this discovery of a possible fifth force would completely change our understanding of the universe, with consequences for the unification of forces and dark matter."

Feng and his colleagues analyzed data gathered recently by the Hungarian who were trying to find dark photons. Dark matter constitutes some 85 percent of all matter in the universe, but it neither absorbs nor emits light, making it impossible to detect directly.

The new work by Feng and his team suggests what the Hungarians found wasn't a dark photon but a "protophobic X boson."

This is a strange particle whose existence could indicate a fifth force of nature.

Electromagnetic force, one of the fur fundamental forces, acts on protons and electrons. The newfound protophobic X boson, however, apparently interacts only with protons and neutrons, and then only at very short distances.

"There's no other boson that we've observed that has this same characteristic," said study co-author Timothy Tait, also a professor of physics and astronomy at UC-Irvine.

"Sometimes we also just call it the 'X boson,' where 'X' means unknown."

The potential fifth force might be linked to the electromagnetic and strong and weak nuclear forces as manifestations of one grander, more fundamental force.

It's also possible that the universe of "normal" matter and forces has a parallel "dark" sector, with its own matter and forces, said Feng.

"It's possible that these two sectors talk to each other and interact with one another through somewhat veiled but fundamental interactions," Feng said.

"This dark-sector force may manifest itself as this protophobic force we're seeing as a result of the Hungarian experiment. In a broader sense, it fits in with our original research to understand the nature of dark matter."