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Tommaso DorigoRSS Feed of this column.

I am an experimental particle physicist working with the CMS experiment at CERN. In my spare time I play chess, abuse the piano, and aim my dobson telescope at faint galaxies.... Read More »

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Yesterday somebody asked me here if I could explain how does a muon really decide when and how to decay. I tried to answer this question succintly in the thread, and later realized that my answer, although not perfectly correct in the physics, was actually not devoid of some didactic power. So I decided to recycle it and make it the subject of an independent post.

Before I come to the discussion of how, exactly, does a muon choose when and how to decay, however, let me make a few points about this fascinating particle, by comparing its phenomenology to that of the electron.
Cannot resist posting the following paperclip, grabbed from a news site this afternoon (it's a Sunday, a critical detail you should not overlook; and this is an Italian newspaper, as should be obvious).



The piece reports news on the Chilean earthquake. Here is a quick-and-dirty translation of the relevant part: "In Conception 350 buried under the rubble. Jackals in action. The government imposes the offside."
The CDF collaboration has recently released new results from a search for what is probably the clearest signature of Higgs boson decay: pairs of high-mass photon candidates. I am very glad to see this new analysis out for publication, since so far only DZERO, CDF's competitor at the Tevatron, had produced results on this particular final state.
"We were not yet prepared to claim that we had found a new charged lepton, but we were ready to claim that we had found something new. To accentuate our uncertainty I denoted the new particle by U for unknown in some of our 1975-1977 papers. The name came later. This name was suggested by Rapidis, who was then a graduate student and had worked with me in the early 1970s on the problem. The letter is from the Greek for "third" -the third charged lepton".
One of the few physics measurements that the LHC experiments are already in the position of producing, with the week-worth of proton-proton collision data they have collected last December, is that of the Bose-Einstein intereference between identical bosons.
There are twenty-four elementary fermions in the standard model. Sure, they are arranged in a very tidy, symmetrical structure of three families of eight fermions (two leptons and six quarks), which is not too unpleasant to behold. And of course, if one is willing to forget the fact that the quantum-chromodynamical charge of quarks does make them different, then the picture is even tidier: 12 fermions, six of them quarks and six of them leptons, arranged in three families of four.