School of Physics Experimental Particle Physics

B Factories

How we study CP violation

While CP violation in neutral kaons was discovered in 1964, it was not until the 1990's that the suggestion of CP violation was observed in other particles. This lead to the creation of B factories, or particle accelerators designed for the production of B mesons.

B mesons are particles composed of a bottom quark (b-quark) and a quark of another flavour. B mesons are desirable for the study of CP violation due to the number of CP violating processes that can be observed in their decay. B factories collide particles at the Upsilon(4S) resonance, meaning that they collide at a centre of mass energy equal to the mass of the Upsilon(4S). The Upsilon(4S) has a mass at just higher than the energy required to create a pair of B mesons. Upsilon(4S) particles will decay in to a pair of B mesons 96% of the time.

Since the Belle experiment began running in 1999, over 700 million B meson pairs have been observed.

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