Giant atom smasher back in business after 2-year upgrade

Scientists successfully restarted experiments at the world's biggest particle collider Wednesday, after a two-year shutdown and upgrade that allows it to smash together atoms with almost double the energy used in its first run.

Over the last couple months, the machine has been going through rigorous testing to prepare for its return to studying the mysteries of dark matter, antimatter and the conditions of the universe at the time of the Big Bang. Early Wednesday, engineers achieved a "stable beam" in the machine, signaling the start of experiments. Eventually, it will ramp up to producing as many as 1 billion particle collisions per second.

The European Organization for Nuclear Research, or CERN, said the Large Hadron Collider will now run around the clock for the next three years, producing vast amounts of data for scientists to scour.

"We have seen the first data beginning to flow," said CERN's director, Rolf Heuer. "Let's see what they will reveal to us about how our universe works."

The collider underwent a $150 million upgrade after its first run, which produced results that helped confirm the existence of an elusive subatomic particle, the Higgs boson.

Heuer said physicists hope the new run might lead to discoveries that could help "explain remaining mysteries such as dark matter."

The LHC, located in a 27-kilometer (16.8-mile) tunnel beneath the Swiss-French border, is now smashing together protons at 13 trillion electronvolts.