With the help of the Large Hadron Collider’s (LHC) heavy-ion detector ALICE (A Large Ion Collider Experiment), physicists have confirmed there is a fundamental symmetry in nature. By making precise measurements of particle mass and electric charge, researchers from the University of São Paulo (USP) and the University of Campinas (UNICAMP) confirmed the symmetry between the nuclei of particles and antiparticles in terms of charge, parity, and time (CPT). The results were published in Nature Physics on August 17 and will help scientists better understand the laws of our Universe.
The team used ALICE – an instrument known for its high-precision tracking and identification capabilities – to take measurements of particles produced from high-energy heavy-ion collisions. The purpose of their experiment was to look for subtle differences in the ways protons and neutrons join in the nuclei and then compare that to how antiparticles join in the antinuclei. The researchers are also hoping ALICE will help them better understand how heavy quarks – such as the charm and beauty quarks – are produced.
"After the Big Bang, for every particle of matter an antiparticle was created. 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 Marcelo Gameiro Munhoz, a professor at USP's Physics Institute (IF) and a member of the Brazilian team working on ALICE.
In their experiment, the researchers measured differences in the mass-over-charge ratio for deuterons and antideuterons along with helium-3 and antihelium-3. Researchers took that data and combined it with recent high-resolution measurements comparing proton and antiproton properties. As we know, the LHC is a massive particle accelerator and ALICE is a specialized instrument that looks for heavy-ion (lead) collisions. When lead ions collide, they produce a massive amount of particles and antiparticles. Data shows these particles combine to form nuclei as well as antinuclei at almost the same rate, allowing for a detailed comparison.
The team measured both the curvature of particle tracks within the detector’s magnetic field and the particles’ flight time in order to calculate the mass-to-charge ratios. After measuring both the curvature of particle tracks in the detector's magnetic field and the particles' time of flight, that information was then used to determine the mass-to-charge ratios for nuclei and antinuclei.
There are many theories regarding the fundamental laws of the universe and the measurements of mass and charge conducted in this experiment are an integral part that will help physicists determine which theory reigns supreme. Scientists are hopeful that by understanding these results, they will better grasp the relationship between matter and anti-matter.
"These laws describe the nature of all matter interactions," Munhoz explained in a statement, "so it's important to know that physical interactions aren't changed by particle charge reversal, parity transformation, reflections of spatial coordinates and time inversion. The key question is whether the laws of physics remain the same under such conditions."