Saturday, March 05, 2011

CDF: a new confirmation of top quark pair asymmetry

Just a few links and remarks.

In January, we looked at a reported huge 3-to-1 asymmetry of the top-antitop (vs antitop-top) quark pairs produced inside the CDF detector at the Tevatron. The effect occurred for high invariant masses - above 450 GeV - and depended on muons.

The strength of the deviation was 3.4 sigma.

Now, Jester has pointed out that a new two-sigma deviation has been publicized by an Asian-Slovak-Californian CDF group.

The new deviation doesn't depend on muon detection - it almost completely boils down to electrons. So the case for the hypothetical asymmetry in the actual laws of physics - that dramatically exceeds the asymmetry predicted by the Standard Model - has strengthened again.

Recall that it is not trivial to obtain such a large asymmetry as a prediction from a theory and the most straightforward way to get such an asymmetry from an interference is to allow, aside from an intermediate gluon, another bosonic intermediate state with the same (adjoint) color charge - such as a heavy gluon in RS-like theories with extra dimensions. Unless I am missing something, a heavy scalar in the adjoint could do the job, too.

More speculatively, the effect could be caused by some coordinated flavor-changing processes, turning the initial light quarks to top quarks; by excited stringy-like cousins of the gluons; or by mundane physics of the Standard Model that has been misunderstood (for example, maybe, one should consider some top-antitop bound state in the adjoint as an independent possible intermediate state?).

Of course, if the experiments continued to suggest that something like that exists, it would be kind of surprising although it is not quite true that such models are completely unfamiliar in the literature. For example, so far, a convincing experimental discovery of a new boson in the adjoint would leave the theorists asking the familiar question "Who ordered that?"

Lorentz invariance at the Planck scale

I decided not to write a separate blog entry about this topic. But as you may know, the Fermi satellite has shown that the Lorentz violation even at the Planck scale must be much smaller than O(100%).

However, I wasn't quite aware of the fact that the vacuum birefringence allows one to make a vastly more stringent ccnstraint than the measurement of the simple delay of the photons: the Lorentz violation at the Planck scale - by the 1/M_{Pl} operators - has to be smaller than 85 x 10^{-15}: the key symmetry is more accurate than a part per trillion. A gamma ray burst was used, too. See
New Limits on Planck Scale Lorentz Violation from Gamma-ray Burst Polarization

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