Divining the matter-antimatter puzzle

Using the world’s highest-energy proton beam at the Fermi National Accelerator Laboratory in Batavia, Ill., three UW–Madison scientists were among 85 researchers from 12 institutions whose recent experiments helped peel away some of the mystery surrounding the relationship between matter and antimatter.

Physics Professor Albert Erwin, assistant scientist Theodoros Alexopoulos and physics graduate student Ashkan Alavi-Harati were part of a team that reported Wednesday, Feb. 24 the discovery of an entirely new type of inequality between matter and antimatter.

First discovered in 1932, antimatter is an important constituent of the Standard Model of physics, which holds that every particle of matter has a corresponding antiparticle of antimatter. The antimatter counterpart of the electron, for example, is the positron.

The theory holds that early in the history of the universe, matter and antimatter were equally abundant. Today, it appears that nature favors matter, however, with antimatter particles found only in cosmic ray interactions — and in the high-energy collisions created by physicists in particle accelerators like Fermilab’s Tevatron.

The new result is of interest because it helps flesh out a model that may help explain what physicists call charge-parity violation, their name for nature’s apparent preference for matter over antimatter. The phenomenon was first observed indirectly in 1964 when physicists James Cronin and ValVitch observed the unbalanced mixing of neutral subatomic kaon particles with their antiparticles, work that yielded the pair the 1980 Nobel Prize in physics.

The latest result is the observation of direct charge-parity violation, providing a framework of evidence against which to test a model of physics that accounts for the phenomenon.