Matter-antimatter symmetry measurement sets new precision record

CERN's ALPHA collaboration has achieved a new precision record in measuring the ground-state hyperfine splitting in antihydrogen, finding it to be identical to that of normal hydrogen to within four parts per million. This level of precision is two orders of magnitude more accurate than previous experiments. While the measurement did not uncover any differences between matter and antimatter, it remains a significant milestone in the quest to understand why the universe predominantly consists of matter.

According to the Standard Model of particle physics, matter particles should have corresponding antimatter particles that are identical except for their charge and magnetic properties. If this theory holds true, the Big Bang should have produced equal amounts of antimatter and matter, yet the universe is largely composed of matter.

This discrepancy has puzzled physicists for years. Measuring antihydrogen, which consists of an antiproton and an antielectron, helps researchers detect potential asymmetries that might explain why matter triumphed over antimatter. The ALPHA-2 antihydrogen apparatus at CERN's Antiproton Decelerator Facility confines the antimatter in a Penning–Malmberg trap to prevent annihilation with normal matter.

ALPHA focused on hyperfine splitting, which occurs due to magnetic interactions between the spins of the antiproton and positron, causing the positronic ground state to split into four sublevels. By measuring these levels' frequencies, researchers calculated the hyperfine splitting energy. Previous measurements had achieved a precision of 400 parts per million, but this new result pushes the boundary to 4 parts per million.

While this increase in precision brings experiments closer to the structure of the antiproton, it still falls short by five orders of magnitude compared to measurements in ordinary hydrogen. Nevertheless, the current models of physics still hold true at this level of precision.