The Large Hadron Collider (LHC), the world’s largest machine, successfully circulated two beams simultaneously for the first time, following the reactivation of the device on November 20. The European Organization for Nuclear Research (CERN), a Geneva-based particle physics laboratory which built the LHC, spent more than a year repairing the $10 billion device, built with the intention of testing various predictions of high-energy physics, when, due to a fault between two superconducting bending magnets, the project was brought to halt soon after the first tests began in September 2008.

Circulating two beams simultaneously allows the operators to test the synchronization of the beams and give the experiments their first chance to look for proton-proton collisions. With just one bunch of particles circulating in each direction, the beams can be made to cross in up to two places in the ring. CERN announced from early in the afternoon, the beams were made to cross at points one and five, home to the A Toroidal LHC Apparatus (ATLAS) and Compact Muon Solenoid (CMS) detectors, both of which were on the look out for collisions. ATLAS was designed to observe phenomena that involve highly massive particles that were not observable using earlier lower-energy accelerators and CMS is designed as a general-purpose detector, capable of studying many aspects of proton collisions.

Later, beams crossed at points two and eight, A Large Ion Collider Experiment (ALICE) and LHC-beauty (LHCb). ALICE is optimized to study heavy ion collisions, while LHCb is particularly aimed at measuring the parameters of CP violation in the interactions of b-hadrons (heavy particles containing a bottom quark, or beauty). Beams were first tuned to produce collisions in the ATLAS detector, which recorded its first candidate for collisions on Tuesday afternoon. Later, the beams were optimised for CMS. In the evening, ALICE had the first optimization, followed by LHCb.

“It’s a great achievement to have come this far in so short a time,” said CERN director general Rolf Heuer, noting these developments come just three days after the LHC restart. “But we need to keep a sense of perspective – there’s still much to do before we can start the LHC physics program.”

Since the start-up, the operators have been circulating beams around the ring alternately in one direction and then the other at the injection energy of 450 GeV. The beam lifetime has gradually been increased to 10 hours, and on Tuesday beams have been circulating simultaneously in both directions, still at the injection energy. CERN said next on the schedule is an intense commissioning phase aimed at increasing the beam intensity and accelerating the beams. All being well, by Christmas, the LHC should reach 1.2 TeV per beam, and have provided good quantities of collision data for the experiments’ calibrations, the organization noted.

“This is great news, the start of a fantastic era of physics and hopefully discoveries after 20 years' work by the international community to build a machine and detectors of unprecedented complexity and performance," said ATLAS spokesperson Fabiola Gianotti.