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### That was fast: First LHC Physics Paper

The first physics paper using LHC data has appeared this morning on the ArXiv:

http://arxiv.org/abs/0911.5430

Out of 284 events taken on Monday at injection energy (900 GeV center of mass) the ALICE collaboration has pulled a measurement of the particle density around mid-rapidity (the center of the detector, e.g. large angles with respect to the beam). The main detector for this measurement was the silicon pixel detector, with the outer silicon layers and the VZERO detector (a beam-beam counter made out of scintillators on both sides of the interaction region, which can thus determine if a reaction took place in the center of the detector) used as cross-checks. Such measurements were also usually the first ones to come out from the RHIC (the Relativist Heavy Ion Collider at Brookhaven) runs, since they involve only particle counting, and are thus relatively fast to accomplish. Still, it requires good control and understanding of the detector. At RHIC, the silicon tracker of the PHOBOS experiment was usually the first one to provide a measurement.

The results of ALICE are nicely consistent with measurements done at the SppS collider (the CERN SPS, used as a collider for protons and anti-protons, which discovered the W and Z bosons) some 20 years ago. So, it is not “New Physics” yet, but it is an impressive achievement none the less: Just one week after the first collisions, which was not even a real “physics” run, the first paper is out. I’m (almost) speechless… That is definitely a way to spice up breakfast!

Congratulations to ALICE, and the whole LHC crew!