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Holiday Chess Riddle

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Why Measure The Top Quark Production Cross Section?

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Tommaso DorigoRSS Feed of this column.

Tommaso Dorigo is an experimental particle physicist, who works for the INFN at the University of Padova, and collaborates with the CMS and the SWGO experiments. He is the president of the Read More »

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The mass of the top quark is a very important parameter of the standard model: using its value together with other no less fundamental ones (the W boson mass, the Higgs mass, and many parameters describing the properties of Z bosons) it is possible to study in great detail the predictions of the theory. In particular, due to the way heavy particles influence the Higgs field, one may verify the consistence of the standard model by looking at a graph where the top quark mass is in the x axis and the W boson on the y axis: different hypotheses for the Higgs boson mass then lie on different parallel curves. One example of such a graph is shown below. It is too complex to discuss it in detail here, but if you are curious I can supply more information in the comments thread.
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Apr 02 2014 | comment(s)

As I mentioned a few months ago, lately I have been writing a science book for laymen. The idea is to focus on the history of CDF, a particle physics experiment that collected data from 1985 to 2011 at the Fermilab laboratory near Chicago.
Now that we know that the Higgs boson has a mass of 125 GeV and displays all the properties that a regular standard model Higgs boson should have, one question you could ask is, is it possible that a top quark decays into a Higgs boson ?

The question is a legitimate one since the top quark has a mass 40% larger than the Higgs, so in principle a decay could be allowed. For instance, one could imagine that the top "fluctuates" into a bottom quark - W boson combination, then that the W boson emits a Higgs particle, and finally the bottom quark and W boson fuse themselves into a charm quark. Or, once the top fluctuates into a Wb pair, it is the bottom quark which emits the Higgs boson before rejoining with the W creating a charm quark. The diagrams are shown below.
I received the following comment from Bo Thide', one of the authors of the paper where Fabrizio Tamburini and collaborators explain their novel method to multiply the transmission of information via EM waves (see here). I think his points are of interest to many so I decided to elect his comment to a independent posting here.

By the way, Bo Thide' is a Swedish professor at the Uppsala department of Physics and Astronomy. For his CV see here.

Comments welcome...

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From Bo Thide':
At 125 GeV of mass, the Higgs boson is a very heavy particle; yet its natural width is predicted to be of just 4.15 MeV in the standard model, a value much smaller than that of particles of similar mass. The top quark, for instance, has a width of 1.5 GeV; and the Z boson has a width of 2.5 GeV: three orders of magnitude larger.
The tau lepton is a particle of very complex phenomenology. Although point-like as its lighter counterparts - the electron and the muon - the tau has a quite respectable mass, 1.77 GeV, which makes all the difference from the other charged leptons.

The tau was discovered in 1975 by Martin Perl at the SPEAR electron-positron collider. The acceptance of that observation was quite slow: the events found by Perl and his team were complicated because of the peculiar properties of the newfound particle. Perl had found an excess of events featuring an electron and a muon and an energy imbalance, which were hard to explain unless hypothesizing the creation of a pair of short-lived, heavy leptons.