After seven months of obliterating protons, the 17-mile-around Large Hadron Collider paused this morning to switch over to smashing lead ions (atoms of lead stripped down to their dense cores).

The goal is to recreate the energy of the universe back to just millionths of a second after the Big Bang.

"The LHC's lead-ion collisions may generate temperatures up to 500,000 times hotter than the center of the sun," Timothy Hallman, a physicist at the Science for Nuclear Physics in Washington D.C., said in a release.

Around those temperatures, quarks and gluons – the "glue" that binds quarks into protons and neutrons – are in a plasma-like state. Hallman said recreating the ultra-hot conditions with collisions between lead ions may "provide vital insight" into how the universe evolved at such a crucial time.

The LHC, situated underneath the French-Swiss border and operated by CERN, paused proton collisions around 3 a.m. EDT this morning. For the next month, physicists will collide heavy lead ions that are expected to generate roughly 10,000 particles per collision. Three cylindrical, colossal detectors hugging the LHC's beamline – known by their acronyms ALICE, ATLAS and CMS – will record the resulting particle soup.

Once the lead-ion collisions wrap up in December, engineers will perform two months of maintenance to allow the LHC to pick up in early 2011 where it left off with proton collisions today. Meanwhile, seven months' worth of proton-collision data awaits physicists hunting for shadows of the Higgs boson – the particle theorized to give matter its mass – in the energetic collisions.

"Over the last seven months, the intensity of the LHC's proton beams has increased 200,000 times," Dennis Kovar, a nuclear physicist at the U.S. Department of Energy in Washington D.C., said in a release. That collision intensity has led to double the data physicists around the world were hoping for, and could speed discovery of weird new particles including the Higgs.

"The eyes of the world might be on the hunt for the Higgs boson, but ... there is a wealth of physics research being done using the LHC's proton collisions," Joseph Dehmer, director of the National Science Foundation’s physics division, said in release.

The collider is not only the biggest ever built, but the most costly at an estimated $9 billion. And so far it hasn’t had an easy time trying to unravel the universe's mysteries.

Shortly after engineers ramped up the LHC in September 2008, faulty wiring between two particle-corralling magnets sprung a leak in the machine's extensive liquid helium cooling system. The mishap flooded part of the subterranean tunnels with 6.6 tons of ultra-cold fluid, causing the helium to rapidly evaporated into gas and damage magnets at the leak site.

Engineers repaired the immediate damage, but unless the faulty connections are replaced, the LHC can't reach its promised particle-colliding power of seven times better than the Tevatron in Illinois (the second-most-powerful in the world). For now it's restricted to being about 3.5 times more powerful than the Tevatron.

To replace the faulty magnet-to-magnet connections, CERN plans to shut down the LHC for 16 months starting in December 2011. The window may leave an opportunity for the Tevatron to help verify, or trounce, the existence of the Higgs particle.

Images: 1) A simulation of the particle soup the ALICE detector at the LHC will see. / CERN. 2) The source of led ions held by Detlef Kuchler, a physicist in CERN's beams department. / M. Brice/CERN.

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