The Standard Model predicts that regular matter B s mesons are slightly favored in these oscillations over their antimatter counterpart, making strange B mesons of special interest to particle physicists. The observation of the B – B mixing phenomena led physicists to propose the construction of B-factories in the early 1990s. They realized that a precise B – B oscillation measure could pin down the unitarity triangle and perhaps explain the excess of matter over antimatter in the universe. To this end construction began on two "B factories" in the late nineties, one at the Stanford Linear Accelerator Center (SLAC) in California and one at KEK in Japan.