FIVE DETAILS ABOUT THE FIFTH FORCE
1 PINPOINTED PARTICLE
In 2015, evidence of a fifth force was first spotted by the physicists in the radioactive decay of beryllium. Now, they have spotted a second example of this fifth force in an experiment involving helium, to go along with the particle they believe is carrying it. They’ve called the particle X17.
2 EXPERIMENTATION
In 2015, researchers at the Institute for Nuclear Research (Atomki) in Hungary started by firing protons at the isotope lithium-7, creating beryllium-8, an unstable isotope, to analyze how it would emit light as it decays. The decay didn’t go as expected. The beryllium-8 should transform into a positron and an electron, and as the energy of the light increases, the angle between the two particles should decrease and eventually separate completely. The physicists observed the two separate at an angle of 140 degrees; they believe that at the moment the atom decays, the excess energy created a new particle. Once that particle decayed, almost immediately, it turned into a recognizable positron and electron.
3 A NEW BOSON
The experiment was repeated with the same results by American researchers. It’s believed a whole new particle could, in fact, be responsible for the anomaly as its characteristics imply it’d have to be a completely new kind of fundamental boson (a particle that can carry forces). It’s described as a “protophobic X boson.”
4 DISTINCTIVE MASS
Three of the four known fundamental forces have bosons that carry their messages of repulsion and attraction. The force of gravity is carried by a hypothetical particle known as a graviton, which scientists have yet to detect. This new boson could not be one of the particles known for carrying the four already established forces, because of its distinctive mass — 17 megaelectronvolts, about 33 times the size of an electron. It also has a tiny lifespan of about 10 to the minus 14 seconds.
5 SEPARATION SURPRISE
The team changed their focus from looking at the decay of beryllium-8 to the state of an excited helium atom. Instead of separating at a 140-degree angle, the positrons and electrons separated at closer to 115 degrees. They calculated the helium’s nucleus, which could have produced a boson with a mass just under 17 megaelectronvolts, which is why they’re calling the particle X17. But it’s still a long way from being known as an official particle that can be added to models of matter.