B-mesons (and anti-B-mesons), that are mesons containing b-quarks, are produced in electron-positron collisions and decay afterwards into many possible final states. The Babar detector is built for reconstructing these B-meson decays. The measured decay time distribution of B-mesons and anti-B-mesons, which decay into the same final state with defined CP quantum numbers, are not equal. This reflects CP-violation in the B-meson system as illustrated in the figure shown.
Figure: The measured decay time for B-mesons (blue) and anti-B-mesons (red)
CP-violation and matter-antimatter-asymmetry
In the universe, there is an imbalance between matter and anti-matter, which is called matter-antimatter-asymmetry. The formation of baryons and anti-baryons in the early universe, called baryogenesis, has to explain this asymmetry. One essential ingredient for a dynamical generation of more matter than anti-matter is CP-violation.
The amomunt of observable CP-violation in the B-meson-system can be predicted by the Standard Model and is generated through a phase in the Cabibbo-Kobayashi-Maskawa (CKM)-matrix. This matrix connects the weak interaction eigenstates of quarks (or anti-quarks) to the mass-eigenstates of the quarks. The Standard Model prediction of CP-asymmetries in the B-meson system can be checked with the measurements of the BABAR experiment.
Link to the BaBar-Webpage: http://www.slac.stanford.edu/BFROOT
Contact: Prof. Dr. H. Lacker