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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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Do you remember the X(3872) ? This is a hadron containing charm and anticharm quarks, which was observed to decay into a J/Psi meson, a positive, and a negative pion. When it was discovered, by the Belle experiment in 2003, the X caused a lot of interest among spectroscopists, because it is an "exotic" charmonium state: its nature is not totally clear, as it might be interpreted as a "molecule" of two charmed mesons loosely bound together. Or maybe a four-quark system ? Or just conventional charmonium, a bit at odds with the expected set of spin-parity states but otherwise just a honest meson ?

In the past few weeks the Tevatron and LHC experiments have updated their results on some of the most important Standard Model parameters. Of these, notably the top quark mass is one where the Tevatron is still doing slightly better than the LHC, due to the longer running time of the CDF and DZERO experiments, which allowed for a more precise calibration of the jet energy scale - the largest systematic uncertainty in this kind of business.

I have updated you on the matter tangentially in the previous two posts, where I discussed the overall compatibility of top and W boson masses with the Standard Model predictions, where the latter depend on the now well-known mass of the Higgs boson. Here instead I want to focus briefly on the top quark mass.

Two days ago I showed how the measurements produced in the course of the last decade have allowed us to "zoom into" the parameter space of the Standard Model, pinpointing the W boson, top quark, and Higgs boson masses to a very narrow 3-D volume of phase space.
The CDF and DZERO experiments recently produced a combination of their precision measurements of the W boson mass, and proceeded to include the LEP II results to obtain a "world average" of that very important parameter of the Standard Model.

The measurement is described in detail in a paper which explains the combination procedure (not trivial, since there are a number of systematic uncertainties that are partly correlated between the experiments). The Tevatron inputs are as follows:

CDF Run I (107/pb, 1.8 TeV): M_W = 80432+-79 MeV
CDF Run II (2.2/fb, 1.96 TeV): M_W = 80387+-19 MeV
DZERO Run I (95/pb, 1.8 TeV): M_W = 80478+-83 MeV
The Dolomites are a mountain range in north-eastern Italy. They take their name from the mineral called dolomite, a carbonate rock which gives these mountains a characteristic pale pink colour, especially notable at sunset. Their composition is also responsible, at least in part, for their shape.

Most of the peaks are in the 2500-3000 meters of height above sea level, the tallest being mount "Marmolada", at 3342 meters. Despite being less tall than other mountain ridges in the Italian Alps, the Dolomites are reknowned for their breathtaking landscapes, as well as for the ski slopes they offer, especially -but not only- in the region around Cortina d'Ampezzo.
Today I received news of an interesting measurement of angular distributions of the decay products in the rare decay of the B meson to  a K* and a muon pair - one of the specialties of the LHCb collaboration, which has more horse-power in some of these low-energy measurements than ATLAS and CMS.