Physics

Amelia Fraser-McKelvie  is not a career researcher or a post-doctoral fellow or even in graduate school, but working on a summer scholarship at the Monash School of Physics, she conducted a targeted X-ray search for the matter called the Universe's 'missing mass' and found it – or at least some of it.

The School of Physics put out a call for students interested in a six-week paid astrophysics research internship during a recent vacation period, and chose Fraser-McKelvie.  Dr. Kevin Pimbblet, lecturer in the School of Physics put the magnitude of the discovery in context by explaining that scientists had been hunting for the Universe's missing mass for decades.
The figure for you to guess which I posted two days ago is built with simulated events featuring the production, at the Tevatron collider, of a Z boson (decaying to electron-positron or muon-antimuon pairs) together with an energetic photon. Apart from Tulpoeid, who of course knew this since Z-gamma production was her PhD thesis topic, only one other reader posted here a solution close to the correct one.
The Upsilon suppression paper by CMS is now public, and you can find it here. I decided to put an entry here since several people asked me to access the information...

Note that this paper is a quite important publication, which not only deals with Y suppression, but more in general with a quantification of dimuon resonance yields. Happy reading!



While the LHC runs like a swiss train and collects dozens of inverse picobarns a day, there's a celebration going on on the other side of the Atlantic, as this picture testifies:



The folks pictured here at the Fermilab village have a reason to cheer up: the glorious Tevatron has just delivered 11 inverse femtobarns of proton-antiproton collisions to CDF and DZERO. What a huge achievement that has been!
Upon being reminded by an automated messaging system, somewhat disturbingly, that today would be the birthday of an esteemed colleague -were he not dead- I decided to post a "guess the plot" entry which pays him a tribute.

The figure below is for you to guess (ignore the blue box at the lower right -it just hides some giveaway information). What does it represent ? What is in the abscissa ? And on the y axis ? Why do the data only populate the upper left half ? And what causes those two funny concentrations ?
Please try your luck and make your guess in the comments thread! It's fun, it's free, it makes me happy to see you considered the riddle, and it adds interest to this column!
The complex plane should be known as the Wessel plane, after the Norwegian-Danish land surveyor. His paper of 1799 was ignored because few were reading the preprint server at that time. Mr. Bookshop in the big city of Paris gets his name associated with graphing complex numbers in a plane. This is one reason I avoid naming things for people as proper credit is complicated.
A few months ago LHC took a special run of proton-proton collisions at  2.76 TeV. Why the lower energy, now that we are accustomed to searching for new phenomena at the highest available energy of 7 TeV ? Because of the wish to compare lead-lead collisions, taken last year at 2.76 TeV nucleon-nucleon energy, with proton-proton ones. The comparison allows to extract extremely interesting results.
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):