Antimatter: Its Origin, Properties, and Mysterious Asymmetry

Friday - November 24 2023, 13:13 UTC - 12 months ago

Antimatter is the opposite of normal matter in every way. Matter and antimatter destroy each other upon contact, so a mystery exists of why there is any matter left in the universe considering it should have all annihilated upon the Big Bang. The Department of Energy Office of Science has numerous research projects around understanding the asymmetry between matter and antimatter.

Antimatter is the twin of almost all the subatomic particles that make up our universe. The matter in our universe comes in many forms—solids, liquids, gasses, and plasmas. These forms of matter all consist of subatomic particles that give matter its mass and volume. These particles include protons and neutrons (also known as baryons), electrons and neutrinos (also known as leptons), and a variety of other particles in the Standard Model of Particle Physics.

Protons and neutrons are themselves made up of particles known as quarks and gluons. But matter can have an opposite in the form of antimatter. In fact, all the subatomic particles in matter either have their own anti-twins (antiquarks, antiprotons, antineutrons, and antileptons such as antielectrons) or they straddle the boundary between matter and antimatter.

These anti-particles can combine to form anti-atoms and, in principle, could even form anti-matter regions of our universe. Scientists believe that these anti-matter regions would have the same physics, chemistry, and other properties. Scientists haven’t seen anti-matter regions in our universe, but they have created copious amounts of antiparticles in particle accelerators and even created anti-elements and anti-atoms. We also know about antimatter from the anti-particles that cosmic ray collisions create. Some types of radioactivity also produce antimatter antiparticles.

Why isn’t antimatter everywhere? When matter and antimatter meet, they annihilate each other, releasing energy. That leads us to the biggest mystery about antimatter. Scientific theories predict that the Big Bang should have created the same amount of matter and antimatter. But if that were true, all the matter and antimatter would have destroyed each other. That would mean there wouldn’t be any matter in the Universe to create stars, planets, or people. Physicists believe that there was one extra matter particle for every billion matter-antimatter pairs. This is more than can be explained by the Standard Model, so scientists are working to understand why.

The Department of Energy (DOE) Office of Science’s High Energy Physics and Nuclear Physics programs have supported research on antimatter for decades as part of DOE’s involvement in fundamental physics research. The Office of Nuclear Physics supports research to understand the asymmetry between matter and antimatter within its Fundamental Symmetries portfolio.

This includes extremely sensitive table-top experiments using neutrons and nuclei and larger scale experiments hosted in deep underground laboratories looking for neutrinoless double beta decay, a predicted nuclear decay that would create two leptons without any accompanying antileptons thus creating more matter than antimatter.

The Office of High Energy Physics (HEP) supports the Deep Underground Neutrino Experiment (DUNE) designed to detect neutrinos created at Fermi National Accelerator Lab. DUNE should be able to tell whether neutrinos are a major contributor to this asymmetry. HEP also supports experiments at high energy particle accelerators that search for differences between matter and antimatter in the deformation of electric charges and in the violation of CP symmetry.