The world's biggest particle accelerator is about to start up again after a two-year shutdown and upgrade.

Scientists at the European Organization for Nuclear Research, or CERN, were preparing to shoot the first particle beams on Sunday through the Large Hadron Collider's 27-kilometer (16.8-mile) tunnel, beneath the Swiss-French border near Geneva.

The collider was instrumental in the discovery of the Higgs boson, a subatomic particle that had long been theorized but never confirmed until 2013.

Scientists are promising nearly twice the energy and more violent particle crashes this time around. They hope the more powerful beam crashes — expected to start as early as June — will give them a peek into the unseen dark universe.