Monthly Archives: December 2009

First results from the LHC

The LHC has been subject to much media coverage and criticism since it was started up last September only to break down little more than a week later, but the first results from the record-breaking particle accelerator are finally in. Admittedly, nothing earth-shattering has been discovered yet, but the turnaround speed of the paper alone must be a record.

The first collisions took place on Monday 23rd November and since then the twin proton beams have reached an energy of 1.18TeV, smashing the previous record of 0.98TeV. Researchers working on ALICE, one of the six experiments within the LHC, however, took data from some of the very first collisions when the protons were circulating at only 450GeV per beam. They had their paper accepted by the European Journal of Physics just 8 days after the collisions took place. Presumably, most of the paper was already written before the LHC was even fired up, with gaps left to fill in the results when they came in.

Before being accepted by the European Journal of Physics, the paper was published online at, an open access repository for scientific papers not yet published elsewhere. Anyone interested in the paper can read it online, but be warned, you’ll have to skip to page 6 to even get to the abstract due to the list of authors (over two pages worth) and involved institutes (more than 100 in total).

In the paper, Aamodt and colleagues describe how some 284 events recorded in the first collisions were used to measure something called the pseudorapidity density of the charged particles. Pseudorapidity is used in particle physics to describe the angle of the particle beam relative to the axis. This may not sound very exciting, but the ALICE collaboration are pleased as the results agree with theory and previous experiments, meaning that the LHC is working well and should provide high quality data to work with when they get to the really interesting stuff.

The first super high energy collisions at the LHC are on track to start in early 2010, and will reach energies of 3.5TeV per beam.

Reference: arXiv:0911.5430v2

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