It has taken 19.5 years to Italy to sanate a wound to its democratic fabric, one which made the country look like a sort of Banana republic, where a tycoon could acquire consensus through his mediatic power, rule unchallenged, and break the law without punishment. But finally we got around it yesterday afternoon, where a vote of the Senate of Republic has decreed that Silvio Berlusconi is unfit to hold a seat in the Parliament.
The top quark is the most massive elementary particle that we have so far discovered at particle accelerators. One usually describes this by saying that the top mass is about 185 times larger than the mass of a whole proton; but since the proton is a composite object, it is not the best comparison stone; I would prefer to compare the top mass to the mass of the lightest quark, which we only roughly know to be in the range of a 2 to 5 MeV. Then one gets a more dramatic picture: the up quark and the top quark are both elementary particles, but the latter is 50,000 times larger than the former. Can that be true ?
In
a paper appeared a few days ago on the Cornell Arxiv Campbell, Ellis and Williams discuss how the LHC experiments have a chance to obtain information on the Higgs boson width by studying four-lepton events at masses much above the 126 GeV region where they cluster when produced by Higgs boson decays. Here I am going to show the graph that is at the source of this idea, and the general conclusions that the theorists reach on the precision that ATLAS and CMS can obtain on that parameter.
First of all let me explain to outsiders what is the Higgs boson width. In order to do so I need to make a short digression.
It happens in 1995, toward the end of Run 1B of the Fermilab Tevatron, in the middle of a otherwise anonymous store. The CDF detector is taking good data, and the shift crew in the control room take care of the usual business - a look at the colourful monitors that plaster the walls, a check at trigger rates, the logging of a few standard warnings issued by the data acquisition system, and the occasional browsing of e-mails.
"This time we're shooting through a brick!"
Larry Nodulman (during a discussion on the reconstruction of electrons in the CDF II detector, just refurbished with a new set of silicon microstrip layers (SVX'), more powerful and capable of identifying the impact parameter of charged tracks with a dozen micron accuracy, but also heavier and bulkier than its predecessor, and thus providing more material for multiple scattering of particles.)
A 1.1 metric Ton satellite will re-enter the earth's atmosphere in the next 48 hours, fragmenting into smaller pieces as it falls. The exact location of the fall is unknown, so you better watch out... Or not.
I was discussing this event with my daughter this morning, and it ended up being an instructive discussion on random events of very low probability. If we are totally oblivious of the satellite orbit, and forget different likelihood of earth surface points for the re-entry (the very north and south latitude are much less likely), we can try and compute how likely it is that one of, say, 50 large fragments of the satellite will end up falling within a 100 m^2 area around us -which would be frightening enough.
A Great Year For Experiment Design
Living At The Polar Circle
Conferences Good And Bad, In A Profit-Driven Society
USERN: 10 Years Of Non-Profit Action Supporting Science Education And Research
