A joint Fermilab/SLAC publication

Large Hadron Collider pauses protons; looks ahead to lead


Simulation of a lead-ion collision in the ALICE detector. Image copyright CERN for the benefit of the ALICE Collaboration.

The LHC's first record-breaking 7 TeV proton-collision run ended today at 8 a.m. Central European Time (3 a.m. Eastern Time). But the LHC's work in 2010 is far from done. The teams running the LHC accelerator and experiments have already begun working feverishly to prepare for the project's next phase: collisions of lead ions.

The change to collisions of lead ions - lead atoms stripped of their electrons - will provide the first full test of the capabilities of the ALICE detector, which was designed to record data from these collisions. It will also mark a temporary change in the research focus for the ATLAS and CMS experiments. All three experiments will use their lead-ion collision data to explore matter as it would have existed in the millionths of a second after the Big Bang. In those early instants the universe was filled with a state of matter called the quark gluon plasma. Probing the QGP and its evolution into the matter that makes up today's universe will shed light on the properties of the force that binds elementary particles - quarks - into bigger objects like protons and neutrons.

Press releases issued today by CERN and by Berkeley Lab, Brookhaven Lab and Fermilab also detail the successes of the proton run that started with a bang on March 30. Over the course of the seven-month-long run, the intensities of the LHC's proton beams increased more than 200,000 times. The teams running the LHC experiments used the first collision data to prove that their brand-new detectors work correctly and to measure properties of known particles at higher energies than ever before. And with even a small amount of proton-collision data from this first low-intensity run, physicists have begun pushing forward the frontier of particle physics, publishing tighter constraints on previously imprecise theories, new limits on the existence of certain hypothetical particles and measuring effects never before seen in proton collisions.

The LHC's first collisions of lead ions are expected to take place in the next few days, and last until December 6. The accelerator will then be shut down for two months for routine maintenance, and will start up with protons again in February 2011.

Check back with symmetry breaking over the coming week to learn how lead ions are accelerated in the LHC, and more about the study of the quark gluon plasma in the ALICE, ATLAS and CMS experiments.

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