As a B- factory (English: B -factory, rarely also: beauty factory ) is called a special accelerator which specializes in the production of B- mesons.
These particles are accelerated (usually electrons and positrons) on opposite circular orbits at an energy of exactly 10,580 GeV in the center of mass system of particles. At this energy resonance occurs, since it corresponds to the rest mass of the Υ ( 4S), an excited state of the connection of a b -quark with an anti -b- quark. A welcome coincidence, it is thanks to them that this energy just only 0.021 GeV in excess of that required for the production of two B- mesons. The decay of the Υ (4S ) into two B mesons (more precisely, Bu, d mesons, since the mass of the Bc, s mesons is already too high ) is therefore highly preferred.
As an experimental advantage turns out to be also the possibility to by a relatively small reduction in the collision energy "turn off" the production of B- mesons. This allows the background of other, unwanted particles study, which is inevitable in particle physics experiments.
Related to the time-dependent CP asymmetry
Since the energy of the resonance is only slightly above the rest energy of the two B mesons, they hardly get kinetic energy, so are almost at rest. To observe interesting effects such as time-dependent CP asymmetries, but it is often necessary that the B mesons move quickly. A so-called Lorentz boost they get by the two colliding beam energies are chosen asymmetrically. This moves the center of the system is not at rest, the B mesons thus move with him in the desired direction, whereby the measurement of decay times by reconstruction of the decay location is possible. This is of crucial importance for the measurement of time-dependent CP asymmetries in the system of neutral B mesons in decays into CP eigenstates, since both B mesons are present due to their generation in an entangled state:
Thus, the time zero is given by the decay of a B meson into a non -CP- eigenstate. Since the decay may have occurred in a CP eigenstate but before that negative time differences are measured in the experiment.
By such precision measurements of B plants could be shown that the observed CP violation on a complex phase of CKM matrix can be recycled. Because of this confirmation of their prediction Makoto Kobayashi and Toshihide Maskawa of the Nobel Prize in Physics 2008 was awarded.
Concrete B- factories
Examples of B- factories PEP - II accelerator at the Stanford Linear Accelerator Center ( SLAC ) in Stanford (USA), which is used for the BaBar experiment, and the KEKB accelerator at KEK in Tsukuba (Japan ), which for the Belle experiment operates. Both B- factories ceased operations (PEP II in 2008, KEKB in 2010).
Under construction in Japan is the SuperB Factory SuperKEKB at KEK, where the successor of the Belle experiment Belle II, is expected to start the data acquisition end of 2016.