A Quantum Diaries Survivor

News from the LHC: the integrated proton-proton luminosity at 7 TeV centre-of-mass energy has generously passed the mark of 40 inverse picobarns yesterday. The CMS experiment alone has integrated over 42 inverse picobarns, as shown in the graph below (the blue curve shows the data collected by CMS, the red one the data produced by the LHC).

The priest of Vigevano's Duomo must have been startled to realize that by far the most faithful presence at mass, ever since the altar was built, is not nonna Pina but a real dinosaur -a glaring testimony of the falsity of catholic-diffused pseudoscience and of the true origin of life on Earth. The red circle in the picture on the right shows the location of the marble slab in the altar.

The CMS experiment has just released a new result which excludes the possibility that quarks have a substructure at energy scales below 4 TeV. The result comes from the analysis of just a handful of inverse picobarns of collision data -2.9 to be precise- and shows excellently just how well suited are the LHC collisions for this business. The limit is extended by over one TeV above the former result of the Tevatron experiments, and some 600 GeV above the results of the ATLAS collaboration, who also recently reported on their search for of quark compositeness in 7 TeV collisions, finding a limit at 3.4 TeV.

Week number one of my course on Subnuclear Gauge Physics is over. I think that in the first five hours of lesson I have given to my students a reasonable picture of the early experimental attempts and theoretical developments aimed at understanding the structure of atomic nuclei and individual nucleons with electron scattering. So I thought I might try and simplify the picture further, to reach a wider audience here. Of course, the topic is not terribly entertaining, unless one understands fully just how important these studies are for fundamental physics even nowadays -despite having started over 60 years back.

As 2010 nears its end, the Tevatron experiments feel the monopoly of top quark physics being taken from their hands, due to the good news on the running of the Large Hadron Collider. The ATLAS and CMS experiments there have started to mine their datasets, now amounting to over 20 inverse picobarns and growing significantly by the day. These datasets contain as many top quark pairs as half an inverse femtobarn worth of Tevatron collisions, due to the 20-fold higher cross section of top pairs at the LHC.

Quite in advance with respect to the stated goals of its 2010 collider program, the Large Hadron Collider has produced yesterday night the instantaneous luminosity of 10^32 cm^-2 s^-1 in the core of the ATLAS and CMS detectors. This is great news for all of us: at such a collision rate, on average one top quark pair is produced every minute, and one 120 GeV Higgs boson (if the thing exists) every 10 minutes makes its apparition there! (Calculations are in this recent post).

Two days ago I wrote here about the projected reach of Higgs boson searches of the Tevatron experiments, discussing what can be seen by CDF and D0 if they combine their analyses results, after improving them as is today thought possible to do. The reach was shown as a function of the integrated luminosity, which allows one to infer what can be done if the Tevatron stops running in 2011 or, as is being proposed, it continues for a few more years.

Last Tuesday I presented new precise Tevatron results on top quark physics at the "LHC Days" conference in Split. The top-quark measurements that CDF and DZERO have produced with their multi-inverse-femtobarn datasets of proton-antiproton collisions are very precise, and they surpass pre-Run-II expectations: suffices to say that the top-quark mass is now estimated with a 0.61% uncertainty, over twice smaller than promised. So it was nice to display these results to an audience mainly composed of LHC colleagues. I received several questions and the interest in my talk was clear.

I am spending a few pleasant days in Split for the conference "LHC Days". I will be representing the D0 and CDF collaborations here in a talk on top physics at the Tevatron; in the meantime, I am pleased to witness that talks are of high quality. This morning the most interesting to listen to (at least to me) was the one by Guido Altarelli, a distinguished theorist from the University of Roma III. Altarelli has given crucial contributions to the advancement of our understanding of Quantum Chromo-Dynamics in the seventies, and it is always a pleasure to listen to him (a previous report of a talk he gave in Perugia two years ago is here).

I will be attending next week to a conference in Split (Croatia). The conference is titled "LHC Days", and has the purpose of bringing together experimental physicists working at the main CERN experiments with theorists and experimentalists from all over the world, to discuss the current status and the future perspectives of research in particle physics, focusing of course on the Large Hadron Collider at CERN.

Georges Charpak, a French physicist and 1992 Nobel Prize winner, died yesterday.Of Polish origin, Charpak gave crucial contributions to experimental physics, in particular for his invention of the multiwire proportional chamber in 1968.Back then, the signal of passage of charged particles was recorded by bubble chamber images and images triggered by spark chambers - where the charge deposition would create a discharge in a very high electric field.

The Large Hadron Collider is increasing gradually the number of proton bunches that circulate in the machine. Yesterday's fill saw 104 colliding proton bunches,  producing the record instantaneous luminosity of 3.5 x 10^31 collisions per square centimeter per second. This is no surprise, of course: luminosity is essentially the product of the number of particles crossing each other per second divided by the cross section of the beams, so if you increase the particles and manage to keep the beam transverse size constant, luminosity must go up.