A Quantum Diaries Survivor

Back from the beautiful Greek island of Naxos, I find myself in Venice for just a day before leaving to another Greek island - Crete. But this time for business rather than vacations: I will be giving a CMS Overview talk at the International Conference of New Frontiers in Physics, which started yesterday in Kolympari, on the north-western coast of the island.As usual, I am lagging behind with the task of putting together my presentation slides. This time I had been working at a reasonable pace while on vacation, and I thought I was almost done, when I was notified that due to the absence of the CMS colleague who was in charge of speaking about CMS Heavy Ion Results, I was to cover in more detail that part than I would have.

Yesterday CMS published the results of a new search for a heavy partner of the bottom quark, by looking for the decay b' -> bZ: that is, the heavy b' is sought in a so-called Flavour-Changing neutral current process. The "neutral current" is an old but still used terminology to indicate the emission of a neutral vector boson, the Z.

Despite the shutdown of the Fermilab Tevatron collider, two years ago, and the subsequent disassembling of the glorious CDF detector, the CDF Collaboration continues to produce excellent physics results using the large bounty of data they have accumulated in the course of the past 10 years.Today you can find in the Cornell arxiv a new paper by CDF, which describes a new very interesting measurement of a property of the top quark - the particle discovered at Fermilab in 1995, the heaviest known elementary particle we know. The property measured is the lifetime of top quarks.

Note: this is the fourth, and last, part of a four-part article (see part I, part II, part III) on the five-sigma criterion for discovery claims in particle physics. If you haven't read the first three installments, the text below may or may not make much sense to you...

Note: this is the third part of a four-part article on the Five-Sigma criterion in particle physics. See part 1 and part 2 to make more sense of the discussion below.

In the previous installment of this longish article, I have introduced some of the issues that may affect the correct interpretation of a statistically significant effect.

A pre-emptive warning to the reader: the article below is too long to publish as a single post. I have broken it out in four installments. After reading the text below you should continue with part II, part III, and part IV (which includes a summary).

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 MeVCDF Run II (2.2/fb, 1.96 TeV): M_W = 80387+-19 MeVDZERO Run I (95/pb, 1.8 TeV): M_W = 80478+-83 MeV

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.