Why do we pay for B-physics?
Because it's the right way to test flavor physics, he argues. Well, then the next natural question is why not T-physics, C-physics, S-physics, D-physics, and U-physics. Yuval answered all these questions. For example, we do not produce too many tops so far - tens or hundreds, and it will jump by a factor of ten at the LHC. There are other problems with the charm quarks, while the u,d,s quarks are viewed as "known".
B-physics is (together with K-physics) a precision science that can be used to argue for new physics indirectly, and I will explain some numbers at the bottom of the text.
It costs a quarter to produce a B today. Another thing that Yuval had to explain is: Why do we need two B-factories instead of one? One of them is in Japan (at KEK) while the other is in California (at SLAC). The answer is that you always want to check things and replicate everything at two places. When Yuval was asked whether we also want to build two LHCs, the answer was "almost yes" - we will have two detectors (ATLAS, CMS) that will compete, and it is always a better approach to build two detectors than one better detector. Well, there will be two more detectors to be built at the LHC - ALICE and LHC-B which is gonna test B-physics.
Yuval continued with "orientation". He explained all the bound states of the b-quark and b-antiquark - B0, B0bar (with the down quark and antiquark, respectively), B+ (with up-quark), Bs (with strange quark) - these are the mesons and heavier relatives of the pion (mesons are quark-antiquark bound states; those without bars contain an anti-b-quark) - and then the less interesting baryons with a single B.
The Upsilon (with "b" and "b-bar") has played a less important role, but he was still producing it from "e+ e-" scattering at a resonant energy.
Every acceptable physics talk today must apparently refer to the anthropic principle. So Yuval explained that the mass of the lightest B meson is 5280 MeV, where 5280 is the number of feet in a mile. Because a mile is an American length unit and both feet as well as America are necessary for intelligent life, the mass of the B meson had to be exactly this number and billions of dollars for B-physics are necessary for intelligent life, too. Because in the context of the anthropic reasoning it is often unclear what is meant seriously and what is a joke, let me mention that I believe that this particular comment about the number 5280 was a joke. Maybe.
Yuval then discussed experiments that have three stages:
- produce many B's
- trigger
- tag
Yuval explained that one can get information about one "b" from the "anti-b" that went in the opposite direction because they're entangled, and he mentioned that the B-factories have been using the EPR phenomenon as a standard identification tool for decades while the people in quantum information and atomic physics pretend that it is extremely original and revolutionary to measure the EPR phenomenon experimentally.
The oscillation rate of B0 to B0bar used to be a big surprise decades ago, but today it's standard physics that is used for calibration purposes and the frequency is known quite well. In the case of B-physics, we are very lucky because the oscillations are almost as fast as the decay of the B's (the ratio is 0.73, and I forgot which way), which is very good for measurements. Similar mesons constructed from other quarks have corresponding ratios that are much smaller or much bigger than one which causes problems.
Yuval also discussed theory. He explained basics about the CKM U(3) matrix (transforming the mass eigenstates of the u,c,t quarks to the SU(2) partners of the mass eigenstates of the d,s,b quarks) with the three CP-conserving angles and a CP-violating phase, and the triangle presentation of its parameters. For the matrix to be unitary, the following sum must vanish:
- sum_{i=u,c,t} V_{bi} V*_{di}
Note that if the CP-violating phase were zero, the three terms above would be real and the triangle would collapse into a degenerate line (two of its angles would be zero). Yuval has also explained why we choose the orthogonality between the b-row and the d-row - the pairs of rows involving the s-row lead to nearly degenerate triangles while the orthogonality of the columns associated with the upper u,c,t quarks is hard to measure.
There have been many details that I don't want to repeat right now - how the different B mesons decay; what are the rates; which processes violate CP and how they're measured; how precisely can we measure various decay rates; how does the box diagram induce the oscillations of B0 into B0bar; which processes in the MSSM can induce the dimensions 6 flavor violating operators such as
- lambda . (d sbar) (d sbar) / Lambda^2.
Note that 10^{4} TeV is a pretty large energy scale that you indirectly test if you study B-physics. The previous sentence should be, however, understood in analogy with the statement that by observing neutrino oscillations, we study the GUT scale physics at 10^{16} GeV. The information is very indirect.
There are several 2-sigma apparent discrepancies known, and most of them will go away. Some of those discrepancies can grow to 3 sigma and higher, but we don't know which ones. Finally, honestly, let me guess that they won't find any deviation from the Standard Model, and if they will, it won't really be clear what is the source.
