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Matter and Antimatter

Matter and Antimatter

For each particle of matter there exists an equivalent particle with opposite quantum characteristics, called an antiparticle. The first antiparticle - the antielectron or positron - was predicted theoretically in 1928 and observed for the first time in 1932.

Particle and antiparticle pairs are created by large accumulations of energy. This is a manifestation of Einstein's famous equivalence between mass and energy, E=mc2. This equation says that given enough energy (which in the case of BABAR is supplied by the particle accelerator PEP-II) and the right conditions, this energy can turn into mass in the form of a particle-antiparticle pair.

Conversely, when a particle meets an antiparticle, they annihilate into an intense blast of energy. At the time of the big bang, the high energy density of the universe must have created equal amounts of particles and antiparticles. But today we don't encounter many antiparticles in everyday life. The question, therefore, is "What has happened to the antiparticles?"

In The question really is "Why is there matter in the universe, while there is no antimatter?" As the universe expanded quickly and cooled, the energy density became too low for the creation of particle-antiparticle pairs, and annihilation should have destroyed all the particles and the antiparticles. But a small fraction (less than one in a billion) of the particles survived and went on to create the matter that is all around us - our bodies, the earth, and the stars we see are all made of matter.

In order to study this question, particle physicists rephrase it in a more scientific way: "what are the differences between matter and antimatter, are they large enough to measure experimentally, and what do they tell us about what happened in the early universe?"

BABAR and Belle have made precise measurements of matter-antimatter differences (called "CP violation"), revolutionizing what had previously been a little-understood aspect of the physical world. Still, the level of CP violation observed in today's experiments is about a billion times two weak to have created the overabundance of matter over antimatter in the universe. This tells us that there are new sources of CP violation that we have not yet been able to determine. BABAR and other experiments are continuing to explore this question with improved precision and sensitivity to new physics.

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