The Plot Of The Week – A Black Hole Candidate

CMS has recently produced an updated search for black hole production in the 7 TeV proton-proton collisions delivered by the LHC. The data sample now consists of 190 inverse picobarns of collisions collected in 2011, and the limits set on black hole production are more stringent.
The search uses a variable called “S_T”, which is the sum of transverse energies of all energetic objects detected in the final state: jets, but also, when present, electrons and muons, as well as photons and missing transverse energy. This variable would be sensitive to the production of black holes, which would produce a enhancement in the high-end of the S_T spectrum. In the figure below you can see what I am talking about, for the subset of events having at least six identified bodies with transverse energy above 50 GeV:
As you can see, the data (black point with error bars) follow the blue background prediction, while enhancements (the dashed curves) would be present at large S_T if black holes existed with the parameter values specified. There are some very high-S_T events in the tail of the distribution, but they are compatible with expected backgrounds; from the agreement, limits can be set on the existence of black holes.
The figure below shows a nice event display, where ten energetic jets are produced together. Calling this a “black-hole candidate” would appear sensationalistic, but it is actually what the CMS experiment does in its public document.


An event display of a N = 10 black hole candidate with ST = 1.1 TeV (Run 163332, Event 196371106). Top: the transverse view of the event with 10 objects (jets) highlighted with magenta cones. Bottom: the zoom on the vertex region in the view parallel to the beam-line. All the jets clearly come from the same, primary vertex (red dot), despite a number of pile-up vertices (blue dots). The nominal beam-spot position is shown with an orange dot.

The detector in this graph is seen in its transverse view, just as if you were looking at it from the beam line. Charged tracks are emitted in all directions, and they cluster in 10 different jets of hadrons, which produce as many energy deposits in the calorimeter. The latter are displayed as red and blue bars outside the schematized detector view.
By Tommaso Dorigo


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