Physics

Just a short post to mention that the Large Hadron Collider has reached tonight the top instantaneous luminosity of 1.075 * 10^33 cm^-2 s^-1. This is a new record for high-energy hadron colliders, improving over precedent records already set this year by the CERN machine. The peak luminosity is 2.5 times larger than the highest reached at the Tevatron (which, one needs to remember, collides protons against antiprotons, and the difficulty in producing the latter makes the comparison between LHC and Tevatron luminosity a bit deceiving).
The plot of the week is actually a table this week. A histogram with several background components can be extremely informative, but sometimes a table provides more detail and one can focus better on interesting features.

The table below has been produced in a CDF search for events containing same-sign lepton pairs: a striking signature of new physics, faked by very few processes. Because of the paucity of Standard Model sources, even relatively small new physics signals can emerge in such a sample. The CDF analysis is based on 6.1 inverse femtobarns of proton-antiproton collisions collected at the Tevatron during Run II. Let us see what the table tells us.


Quantum mechanics allows us to perform the following experiment (see the article by David Mermin in Physics Today Vol. 38 No. 4):

Modern physics has disproved direct realism: There is no locally realistic description of our world possible. Although I have already explained this differently at several places, for example by refusing 'real stuff' as being a good explanation for what is ‘at the bottom’, it is worth to prove it once rigorously. Let me present the simplest established proof in the simplest possible version that I can come up with. Everybody claiming interest in the interplay between science and philosophy should have gone through this proof at least once and I did my utmost to make it as easy as possible: Only three angles are considered and probabilities almost completely avoided by instead talking about natural numbers like 50.

A question posed by Tony Smith in the thread of the previous post (which dealt with the choice of the bin width in histograms) triggered me to do a little work to produce a convincing answer to him.

The issue is the following. Tony got interested in a few top candidate events in a few mass distributions published by CDF and DZERO quite some time ago, which seemed to all cluster in the surroundings of 145 GeV. Could those eight candidate events (once summed across the various channels and experiments) be the signal of some resonance different from top quarks ?
I was unaware of the following story, which was brought to my attention by Monica Pepe-Altarelli yesterday. Since I totally agree that nobody should be detained without proof of guilt for long periods of time, and since we are talking of a physicist, I am glad to broadcast the story here.
This blog contains four snaky puzzle questions, their back stories, answers, and discussions. Due to family responsibilities, the video blog must be delayed until at least Thursday.
click or skip a reading of this blog:


April 18 - Higgs? We ain’t got no Higgs 
The presentation of data is a very rich subject, on which there is a whole lot to discuss, even by restricting to the issues relevant to our dear field of experimental high-energy physics. Usually too little thought is given to it, even by expert researchers, so I thought that maybe today I would offer here some ideas on one very basic issue, the one of how to choose the width of the bins of a histogram.

Time to reveal the solution to the cat killing mystery introduced in “If Schrödinger's Cats All Die, Do the Alive ones go to Hell?” and further explained in “Rotating Schrödinger's Cat to Death”. The solution is a huge letdown for all cat haters. Instead of being send to hell or at least into a parallel universe where they won’t bother no more, the cats stay right here in our lab! (See Nina – I am not as bad as you think.)

The measurement of the production rate of top quark pairs at the Tevatron is by now a very well developed technology, where it is hard to invent anything new. Eight years ago, however, there was still the chance to develop new techniques and explore new land.