When electron and positron beams of the same energy collide, the subatomic particles that are created fly off in every direction from a single point. This makes it difficult to reconstruct the sequence of events that take place. Putting more energy into the electron beam than the positron beam imparts a net motion to the by-products of the resulting collisions. So events that take place at infinitesimally different times also take place at measurably different locations. The scientists expect the information to offer new insight into the differences between normal matter and antimatter.
Antimatter is the mirror image of normal matter, but with the opposite electrical charge.
For example, an electron has a negative charge. Its antiparticle, the positron, has the same weight and size, but carries a positive charge. Otherwise, matter and antimatter act almost identically. Since antimatter was discovered, scientists have wondered why there is virtually no antimatter in the visible universe. The major arteries of the B-Factory are the two rings.