So far, 2009 has been a much kinder year to the Large Hadron Collider (LHC) than 2008 was. The gargantuan particle accelerator, sidelined for more than a year after a breakdown halted its initial run shortly after start-up in September 2008, has been steadily clearing performance benchmarks since resuming operations on November 20 of this year. In the weeks since the LHC's long-awaited reboot, the collider's operators have been putting the machine through its paces, circulating proton beams in both directions through the collider's 27-kilometer underground ring outside Geneva and later accelerating beams to world-record energies.

Now CERN, the European laboratory for particle physics that runs the LHC, can claim another record for their prized machine. On Tuesday the record-setting beams, accelerated in opposite directions to energies of 1.2 TeV (tera–electron volts), collided for the first time, the most energetic particle crash ever orchestrated in a collider. The reigning champ before the LHC's rebirth was Fermilab's Tevatron in Batavia, Ill., which can accelerate beams up to 0.98 TeV. Over time, CERN plans to ramp up the LHC's beams toward the design energy of 7 TeV.

Physicists arrange high-energy collisions to observe the debris they generate: the exotic and short-lived particles that come flying off. Those particles hint not only at the makeup of matter at the smallest scales but also how the largest structures in the universe came to be. The higher the energy achieved, the more closely physicists can replicate conditions that existed shortly after the big bang. For a detailed description of the new realms of physics the LHC could open up, see our In-Depth Report from 2008, when the collider was nearing its first—and ultimately troubled—start-up.

LHC personnel awaiting collisions of 0.9 TeV on December 6: CERN