The Large Hadron Collider (LHC) circulated two beams simultaneously for the first time this week, giving the experiments their first chance to look for particle collisions.

“It’s a great achievement to have come this far in so short a time,” says CERN Director General Rolf Heuer. “But we need to keep a sense of perspective – there’s still much to do before we can start the LHC physics program.”

With one beam circulating in each direction, the scientists made the beams cross at each detector in turn, first at ATLAS then CMS, finally ALICE and LHCb. Each detector will play a role in answering key questions about the nature of our Universe, from 'what is dark matter?' and 'what gives matter mass?' to 'are there any higher dimensions in space?' and 'what were conditions like right after the big bang?'

“The tracks we’re seeing are beautiful,” says LHCb spokesperson Andrei Golutvin, “we’re all ready for serious data taking in a few days time.” These developments come just three days after the LHC restart, following a 14 month delay since its original start up in September 2008, which was short lived due to a fault in one of the cooling systems. The LHC's magnets, which direct the beams around the 27 kilometre track, are designed to operate at -271 degrees Celsius.

Since the LHC was fired up again at the end of last week, operators have been circulating beams around the ring alternately in one direction and then the other at the injection energy of 450 GeV. Over the next few weeks the beam intensity and acceleration will gradually be increased, reaching 1.2 TeV by Christmas and allowing good quality collision data for all the experiments' calibrations.

“Achieving low-energy collisions in the LHC so quickly after the restart is a huge boost for the worldwide particle physics community,” says Norman McCubbin, Head of Particle Physics at the Science and Technology Facilities Council’s Rutherford Appleton Laboratory. “We look forward eagerly to the next stages in commissioning the LHC and to embarking on our quest to unlock new secrets of the Universe as the machine becomes fully operational.”

Read more about the science behind the LHC in our online preview story Powering up the world's biggest physics machine (September 2008) and also The world's biggest machine featured in the July 2008 issue of Astronomy Now magazine.

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