Antimatter is notoriously difficult to obtain and study because it annihilates when it encounters ordinary matter. Researchers at Northwestern University have now trapped a single positron—the antimatter counterpart of an electron—for months. By cooling it to temperatures near absolute zero and controlling it with electric and magnetic fields, the team could manipulate and measure its quantum state without destroying it, creating a new way to investigate why the universe contains so much more matter than antimatter.
Keeping a single antiparticle stable
In theory, antimatter should be everywhere. Mathematical models predict that every particle of matter has a corresponding antiparticle, a prediction that experiments have confirmed. The universe should therefore contain comparable amounts of matter and antimatter, yet nearly everything we observe is made of ordinary matter. Why this imbalance exists remains one of physics’ major unanswered questions.
Although scientists can produce antimatter in laboratories, studying it is extremely challenging. When an antiparticle meets ordinary matter, the two annihilate and release energy. Researchers use vacuum chambers and electromagnetic fields to isolate and suspend antiparticles, but even with those precautions, investigating their behavior—particularly at the quantum scale—remains difficult.
For this experiment, a team led by Gerald Gabriels at Northwestern University captured positrons in a device called a single-positron quantum cyclotron. Electric and magnetic fields held the particle in a vacuum while it was cooled to temperatures close to absolute zero. In this low-energy state, researchers could induce controlled changes in the positron’s quantum behavior.
Unlike techniques that destroy particles during measurement, the new method allowed the same antiparticle to remain trapped for months. Researchers could therefore repeat their measurements and study the particle without having to replace it after each experiment. The findings were reported in Physical Review Letters.
Testing the symmetry between matter and antimatter
Scientists know that matter and antimatter have many closely matching properties. An electron and a positron, for example, have the same mass but opposite electric charges. However, researchers continue to investigate whether the two particles differ in subtle ways that earlier experiments could not detect.
The Northwestern team plans to compare the magnetic properties of positrons and electrons. Physicists can already make highly precise measurements with electrons, but reaching comparable precision with positrons has been more difficult. According to the American Physical Society, the new device could enable measurements of antimatter particles roughly 30 times more precise than previous measurements.
Experiments so far have not identified any unexpected difference between electrons and positrons. The achievement is an improved ability to search for such differences. If future measurements show that positrons respond to magnetic fields differently from electrons, physicists may need to revise some of the laws used to describe matter and antimatter.
This story was originally published in the Spanish edition of WIRED and translated from Spanish.
Source: www.wired.com