National Nuclear Security Administration

NNSA explores unsolved mysteries of science: Why is there more matter than antimatter in the universe?

December 27, 2018

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The Jupiter Laser Facility
The Jupiter Laser Facility

From the massive expanse of outer space to the infinitesimal world of subatomic particles, humankind has relentlessly searched for answers. When an answer leads to more questions, we plunge onward, in perpetual pursuit of knowledge and understanding.

NNSA embodies this sentiment with its fierce dedication to research and development to better serve and protect our nation. The missions of nuclear security depend on leading-edge technologies that lay at the frontiers of science. In this series, we will explore unsolved mysteries of science that NNSA research is investigating.

Antimatter particles share the same mass as their fundamental matter counterparts, but have exactly opposite charges. When a matter-antimatter pair meets, they annihilate each other. Logically, the Big Bang should have created equal amounts of matter and antimatter. If this were true, though, then every particle would have been cancelled out by its inverse, leaving nothing.

Physicists at Lawrence Livermore National Laboratory were able to create billions of positrons (electron antiparticles) using a sample of pure gold at the Jupiter Laser Facility. By creating this many positrons, the scientists hope to study the nature of antimatter in great detail and discover why it is so out-balanced by matter.

The High-Altitude Water Cherenkov Gamma Ray Observatory
The High-Altitude Water Cherenkov Gamma Ray Observatory

The High-Altitude Water Cherenkov Gamma Ray Observatory in Mexico was recently used to help uncover why there is an excess of positrons just above Earth’s atmosphere. It was thought that perhaps a pair of pulsars (neutron stars emitting pulses of radiation at regular intervals) was the culprit, but this was ruled out. That’s because there are a lot more positrons than can be explained by any process we know. The reigning hypothesis is that ever-elusive dark matter is to blame.

Of the various types of antimatter, antineutrinos are of particular interest to NNSA. They are produced during radioactive decay and are impossible to shield – making them perfect targets for monitoring the production of fissile material. Antineutrinos barely interact with other particles, but they are produced by nuclear reactors in massive quantities and are thus easy to spot with the right equipment.

Antineutrinos are so mysterious there is even a theory that antineutrinos and neutrinos are actually the same particle. A phenomenon called neutrino-less double-beta decay would confirm this theory and Los Alamos researchers, along with nearly 30 other institutions around the world, are seeking to observe it in the Majorana Demonstrator experiment.