Scientists have long recognized that there are four "fundamental forces" that govern nature. The matter of our universe is drawn together by these forces, or pushed away by them. Among the four forces are gravitational and electromagnetic forces, which produce important long-distance interactions whose effects can be observed directly in everyday life. There are also two forces called the strong nuclear force and the weak nuclear force, which generate forces at tiny subatomic distances and dominate nuclear physics.
Over the years, there have been many unconfirmed claims that there is a fifth fundamental force in nature, yet long-term efforts to find dark matter have not been fruitful. Dark matter is a theoretically present matter that is supposed to account for 80% of the total mass of the universe, but has not yet been discovered. To fill in the gaps that the Standard Model of particle physics can't explain, scientists have gone the extra mile to find new forces.
Scientists at the Institute of Nuclear Research of the Hungarian Academy of Sciences (Atomki) have officially published their findings, demonstrating the role of the fifth force. Attila Krasznahorkay, the study's chief scientist, said this is the second time his team has detected a new particle, which they call X17 because they calculated its mass to 17 megaelectronvolts, "X17 could be a particle that connects our visible world to dark matter." "
The X17 discovery can be traced back to Krasnahokai's team's study of the radioactive decay of beryllium-8 a few years ago. Ever since Cambridge built the first particle accelerator, and since the discovery of beryllium-8 in the 1930s, the existence of such unstable atoms and their unique way of decay have been the focus of numerous studies related to stellar nucleosynthesis: How exactly do nuclear fusion in stars form elements?
In 2015, researchers found that when protons emit protons toward the lithium-7 isotope that forms beryllium-8, subsequent particle decays do not fully produce the expected light emission, and specific tiny "collisions" occur. This discovery was unexplained by scientists at the time.
If the energy of light is large enough, it transforms into electrons and positrons, which push each other at a predictable angle and then disappear. According to the law of conservation of energy, the angle between two particles should decrease as the energy of the light that produces two particles increases. Statistically, at least. However, researchers in Hungary have found an unexpected increase in the number of electrons and positrons separated as atoms decay, often pushing each other at an angle of 140 degrees.
Since then, Hungarian researchers have shifted the focus from the decay of beryllium-8 to changes in the state of an excited helium nucleus. And there are new advances in their research. They have measured the same result in stable helium atoms, except that the electrons and positrons in the helium atoms are not separated at a 140-degree angle, but are closer to 115 degrees, a feature that is unusually similar to those observed in beryllium-8.
The Hungarian team concluded in the paper that we expect more independent experimental results for the X17 particle in the coming years. As a formal particle, adding it to any model of matter still has a long way to go. If the existence of entirely new particles is confirmed, it means that physicists will have to re-evaluate the interactions between the four fundamental forces that exist in particle physics and make room for a fifth force. Perhaps scientists can better understand the forces that control the universe, and a whole new elementary particle could help scientists completely demystify dark matter, and X17 is exactly what we want.
Jonathan Von, a professor of physics and astronomy at the University of California, Irvine, told reporters he had been following the work of Krasnahokai's team and believed their research was forming a "game changer." If the results of these experiments can be replicated, he says, "it will be a Nobel Prize without a doubt."
(Editor: Chen Xian)