The subject is not only the Higgs mass, but the top quark mass. Which top mass ? The "pole" mass -the real part of the pole in the perturbative top-quark propagator. Have I lost you ? Ok, do not worry -definitions are for theorists. Let us just say that the top quark, being a complicated coloured object which thus cannot live free of the influence of strong interactions,
is measurable at a hadron collider like the Tevatron only within uncertainties of the order of a constant called "Lambda QCD", which is of the order of 200 MeV.
Now, 200 MeV are very little energy, a thousandth of the total top mass, and the Tevatron average for the top mass measurement has a total uncertainty still more than six-fold larger than 200 MeV. However, that intrinsic limitation is getting closer.
In the next article I will explain better what is the cause of this limitation, and I will then describe a new attempt at determining the top pole mass by first computing the "running top mass" -a different quantity, which does not suffer from the mentioned problem. The top pole mass is the important quantity, because with it one can try and compute the Higgs mass, by using radiative corrections to electroweak theory and the measured electroweak parameters, plus the W boson mass measurement.
What I am talking about is a plot like the one below. In it, the W mass is on the vertical axis, the top-quark pole mass is on the horizontal axis, and the diagonal bands show the functional dependence of the Higgs mass on those two parameters. A green-painted region highlights the points of the plane which are favored by supersymmetric theories. However, there is a whole lot to say about that, and I will keep my thoughts for the next article.
For now, you can just admire the new information in the plot, which was provided to me by Sven Heinemeyer the other day. I will also omit to say what is the origin of the blue ellipse, but will just note here, to stimulate your thoughts, that it falls entirely in the MSSM-favored region of the plane!
Comments