Scientists explain why stuff is matter

All down to decay rates, it seems

Miniscule differences in the way antimatter and matter behave may help to explain why the universe is dominated by matter, according to a group of scientists working on the BABAR experiment.

The big bang should have produced equal quantities of matter and antimatter. The fact that our universe is so dominated by matter must be down to some subtle difference in the two substances. The research teams on the BABAR experiment have discovered tiny differences in the decay patterns of B and anti-B mesons, a phenomenon known as a CP violation.

This is one of three conditions outlined by Russian physicist Andrei Sakharov to explain the observed imbalance in the relative quantities of matter and antimatter, and is not easy to find. The differences in the decay patterns that point to a CP violation are tiny: in this case less than 300 parts in 200m pairs of B and anti-B mesons.

The BABAR experiment involves the Stanford Linear Accelerator's PEP II accelerator, which collides electrons and positrons. This collision produces exotic heavy particle and anti-particle pairs known as B and anti-B mesons. In turn, these decay into other subatomic particles, like kaons and pions.

SLAC's Marcello Giorgi, who is also spokesman for the BABAR experiment, said that if there were no difference between matter and antimatter, both the B meson and the anti-B meson would exhibit exactly the same decay patterns. "However, our new measurement shows an example of a large difference in decay rates instead."

Giorgi explained that the team has examined the decays of more than 200m pairs of B and anti-B mesons and found 910 examples of the B meson decaying into a kaon and a pion, but only 696 examples of the same final state for the anti-B. This is what is known as a direct charge conjugation parity, or CP violation: you can read upon that here.

"The new measurement is very much a result of the outstanding performance of SLAC's PEP-II accelerator and the efficiency of the BABAR detector," Giorgi said. "The accelerator is now operating at three times its design performance and BABAR is able to record about 98 per cent of collisions." ®

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