Physics

Swamped by my course of Subnuclear Gauge Physics, I have little time left to surf the web and keep an eye on what happens in the blogs I usually visit. Nevertheless, today is Saturday and I have allowed myself a short tour. Below is a list of the most interesting things I have read. First of all, there's an interesting new blog out there, with experimental particle physics explained to laymen. The language is not English, but it is a language you should learn, too. Peter Woit has news about the Bogdanovs. The whole story is just fascinating - the two brothers are certified cranks, but they…

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. Below you can see a top pair candidate from CMS: the detector is shown from a side, and…

Energy (E) is a useful quantity. It has certain properties and connections with other such measures, like momentum p. E is paired with time t, much like momentum p and distance x are such a pair. This pairing is known from classical mechanics and it shows up in relativity: The merging of t and x into one entity, space-time, leads straight to such a melting also of E and p. In quantum physics, the uncertainty Δx ~ 1/Δp is important, and it translates into Δt ~ 1/ΔE. We do not think that momentum p is a substance! (Update: Here is a post on that energy is not a substance and how to best…

"Since two fermions cannot turn into three fermions, the experimental observation of three-jet events in e+e- annihilation, first accomplished by the TASSO collaboration in June 1979 and confirmed by the other collaborations at PETRA two months later, implies the discovery of a new particle. Similar to the quarks, this new particle hadronizes into a jet, and therefore cannot be a color singlet. These three-jet events are most naturally explained by a hard noncollinear bremsstrahlung . [...] Thus the 1979 discovery of the second gauge particle, the gluon, occurred more than fifty years…

Is energy conserved? "Of course it is!" anyone with just a rudimentary knowledge of physics will answer. A more pertinent answer would be: "if you can't show me a working perpetual motion machine, shut up and stop wasting my time!"  The conservation of energy is an insight that stood the test of time. It was Julius von Mayer who first worded it in its clearest form: "Energy can be neither created nor destroyed". That was nearly 170 years ago.  So why question energy conservation? The interesting thing about physics is that the deeper you dig, the more you are forced to doubt…

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). The figure on the right shows the progress of data accumulation by the CMS detector. THe progress of data collection is…

On October 13th 1985 the Tevatron collider started operations, producing the first man-made proton-antiproton collisions at 1.6 TeV center-of-mass energy in the core of the CDF detector. 25 years have passed. It is frankly unbelievable that the machine is still operating today, and with it CDF, which was back then the only game in town (D0 came later). I find it even more unbelievable if you consider that much of the technology, the magnets, the devices that produced the collisions and the ones that recorded them are still those of 25 years back. 25 years are like a two glaciations time span…

Today (and the next time in this series on duality), I explain the most interesting insight that I have gotten from string theory about black holes. String theory may not be the correct theory of quantum gravity, nor has it modeled any usual black holes yet. Nevertheless, I will neglect these issues and concentrate on the core insight, which is here illustrated best with string theory, although it is not dependent on it. The core insight is one about duality and very similar to what I introduced there. It is less general but very intuitive. I recommend carefully considering this picture, as…

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. The results presented in the graph I published in that post were shown as a "discovery reach", i.e. by showing how significant would be a Higgs…

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. The truth of…