The Large Hadron Collider is due to start producing data again today, after more than two years of maintenance, repair and recommissioning.
The LHC has been offline for 27 months while scientists at CERN in Switzerland upgraded it. It will now be taking measurements at unprecedented energy levels - 13 tera-electronvolts (TeV), almost doubling in power from its first three-year run.
Scientists now hope that the beefed up atom smasher will open the way to new frontiers in physics - but they're already having to wait, after a software fault forced them to cancel the first beams of the day.
Professor David Charlton, a team leader at CERN, has said: "We're heading for unexplored territory. It's going to be a new era for science."
As well as searching for dark matter, scientists hope to discover more and possibly different strains of Higgs boson, investigate anti-matter, and test the theory of "supersymmetry", which predicts that every known particle has a more massive hidden partner.
Two beams of particles sent flying in opposite directions through 16.7 miles of circular tunnels beneath the Swiss-French border, just three metres per second below the speed of light. The energy they they release when they collide is then used to create new and hopefully unknown particles.
The LHC team astounded the world with the discovery of the Higgs Boson, the elementary particle that gives other particles mass, which had eluded detection for nearly 50 years.