Last year, a team of Hungarian physicists spotted an anomaly in a radioactive decay. They detected a curious new particle being emitted, with properties no other particle should have. US theoretical physicists looked into this claim and discovered that not only it does not violate any previous experiments, but it could be a carrier of a mysterious fifth force.
This is not the first time a fifth force has been postulated (the other four being gravity, electromagnetism, strong nuclear, and weak nuclear). Ninety-six percent of the matter-energy content of the universe is made of something other than ordinary matter, and the fifth force is sometimes invoked to explain these mysterious components, called dark matter and dark energy.
The fifth force is also used to explain the limitations of the standard model of particle physics, such as the anomalous magnetic dipole moment, the measurement of which disagrees with the theoretical value.
The Hungarian team was looking for "dark photons," electromagnetic bosons that interact with dark matter. They shot protons at lithium-7 atoms, creating the unstable beryllium-8, which decays in pairs of electrons and positrons (which are anti-electrons). According to the standard model, the number of observed pairs should drop as the angle between the two particles increases. But the team reported an unexpected bump of particles at about 140° before it continued decreasing.
The bump indicates the presence of an intermediate stage, another particle, with a mass of about 17 MeV, which is equivalent to the mass of 32 electrons, and with no electric charge. The team is confident in the detection, claiming that the chance that it’s a fluke is less than 1 in 200 billion.
While the presence of this particle is unexpected and unexplained, many experimental teams are gearing up to confirm this detection. The DarkLight experiment at the Jefferson Laboratory, which is looking for dark photons, will be able to test the claim within a year at most. In Europe, the LHCb experiment at CERN will also be searching for this proposed particle.
It is important to keep a healthy degree of skepticism until the results are confirmed, but maybe we are about to open a window onto completely new physics.