Physics Goals of BaBar

The study of violation in B decays is the primary physics objective of BaBar[].

Up to corrections of order Alamba^4, the penguin diagrams have the same weak phase as the tree diagrams. Thus, these channels have an unambiguous relationship between the measured asymmetry and the angle beta. For channels that measure the angle alpha, the situation is not quite as good, although still satisfactory. In this case, QCD penguin diagrams are expected to give contributions on the order of perhaps 5–20% of the tree amplitude, and they have a different weak phase. In addition, the Z^0-mediated penguin diagram also contributes at the level of perhaps 5% of the tree amplitude, with the same weak phase as the QCD penguins []. Isospin-based analysis can select an isospin channel that has no QCD-penguin contribution []. The uncertainty in extracted from the asymmetry in this channel due to the Z^0-penguin contributions is then not more than 0.05%. This is less than the expected experimental uncertainty.

That is as maybe but I am still in a state of uncertainty.. What do penguins have to do with Quantum Chromo Dynamics?

And, in any case, wasn’t Babar an elephant?


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