The Large Hadron Collider adds another notch to its belt of triumphs: this time, evidence that particles and antiparticles display symmetry in response to the fundamental laws of physics.
Along with every particle of matter in the universe, the Big Bang also created a particle of antimatter. These antimatter particles are identical to their normal twins in mass and structure, except they possess the opposite electric charge. If every particle was replaced with its antiparticle and sent backwards in time, a mirror universe would actually evolve under the same physical laws as our version of the universe.
At least, that’s what the theory for Charge-Parity-Time (CPT) symmetry claims. “Parity” refers to an object’s orientation in three-dimensional space, and a parity inversion would create a mirror image of a particle. Although CPT symmetry constitutes one of the fundamental properties of physical laws, scientists still aren’t sure whether the theory holds true for all physical phenomena. After all, it does sound hard to believe that a mirror image universe would behave exactly the way ours does.
But researchers are honing in on a more comprehensive picture of the physical workings of the universe that includes CPT symmetry, thanks to the Large Hadron Collider’s capacity to recreate the high-energy collisions that characterized the early universe. The ALICE (A Large Ion Collider Experiment) detector on the LHC ring uses high-precision tracking and identification equipment to analyze particles produced from lead ion collisions. These collisions produce both particles and antiparticles in rich, almost equal amounts, allowing for detailed comparisons of their characteristics.
By measuring the way the particles curve through magnetic fields and how long they take to travel, researchers can determine the ratio of mass to charge. Marcelo Gameiro Munhoz and his fellow ALICE team members used these mass-to-charge ratios to compare the formation of nuclei from protons and neutrons with the formation of antiparticles from antinuclei.
“In particle physics, a very important question is whether all the laws of physics display a specific kind of symmetry known as CPT, and these measurements suggest that there is indeed a fundamental symmetry between nuclei and antinuclei,” said Munhoz. This means that even when the particles undergo charge reversals, reflections of spatial coordinates, and time inversions, they still obey the same laws of physics that govern all interactions of matter and antimatter.
This confirmation of CPT symmetry provides valuable insight into the behavior of matter and antimatter. These measurements can be used to finally determine which of the many theories about the fundamental laws of physics is actually true. This experiment and others at the LHC will help physicists get a better grasp of how the universe evolved into its current state, and how it will continue to change in the future.