June 17, 2011 On June 17, 2011 at around 10:50 CEST, the amount of data accumulated by LHC experiments ATLAS and CMS clicked over from 0.999 to 1 inverse femtobarn, signalling an important milestone in the experiments' quest for new physics. The number signifies a quantity physicists call integrated luminosity, which is a measure of the total number of collisions produced. One inverse femtobarn equates to around 70 million million (70x1012) collisions, and in 2010 it was the target set for the 2011 run. That it has been achieved just three months after the first beams of 2011 is testimony to how well the LHC is running.
Among the new physics the LHC experiments are searching for are the Higgs mechanism and supersymmetry. The Higgs mechanism, and its associated particle, is the last missing ingredient of the so-called Standard Model of particle physics that explains the behaviour and interactions of the fundamental particles that make up the ordinary matter from which we and everything around us are made. The Higgs mechanism gives rise to the masses of certain particles.
Ordinary matter, however, appears to be only around 4% of what the Universe is made of. Supersymmetry is a theory that goes beyond the Standard Model. It is a more elegant theory of ordinary matter, and could also explain the mysterious dark matter that makes up about a quarter of the universe. With one inverse femtobarn there's a real chance that, if these theories are correct, they will start to manifest themselves in the data.
A third LHC experiment, LHCb, requires less data than ATLAS and CMS, but has also exceeded its expectations for the year.
Although recording data with proton beams, the fourth major LHC experiment, ALICE, is specifically designed for physics with lead-ion beams, which will come during the last four weeks of the LHC's 2011 run.
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