For each particle of matter there exists an equivalent particle with opposite quantum characteristics, called an anti-particle. Particle and anti-particle pairs can be created by large accumulations of energy and, conversely, when a particle meets an anti-particle they annihilate with intense blasts of energy. At the time of the big-bang, the large accumulation of energy must have created an equal amount of particles and anti-particles. But in  everyday life we do not encounter anti-particles. The question, therefore, is "What has happened to the anti-particles?"

BABAR is a High Energy Physics experiment located at the Stanford Linear Accelerator Center, near Stanford University, in California.

The goal of the experiment is to study the violation of charge and parity (CP) symmetry in the decays of B mesons. This violation manifests itself as different behaviour between particles and anti-particles and is the first step to explain the absence of anti-particles in everyday life.

To study CP violation the BABAR experiment exploits the 9.1 GeV electron beam and the 3 GeV positron beam of the PEP-II accelerator. The two beams collide in the center of the experiment, producing Υ(4S) mesons which decay into equal numbers of B and anti-B mesons.