The Large Hadron Collider (LHC) has been fired up to start delivering physics data for the first time in 27 months, meaning experiments can resume at the world's largest particle accelerator.
It follows more than two years of maintenance and repair as well as several months of recommissioning.
The experiments are set to take data at the unprecedented energy of 13 tera-electronvolts (TeV) – almost double the collision energy of the LHC's first, three-year run.
It is hoped the development will mark the start of season two at the LHC, opening the way to new frontiers in physics.
Due to a software issue the first beams sent this morning had to be stopped, but the experiments are due to resume later.
The £3.74 billion LHC, the most powerful atom-smasher ever built, was restarted in April after a two-year upgrade.
Last month scientists from the European Organisation for Nuclear Research (CERN) achieved test collisions between protons - the ''hearts'' of atoms - at 13 TeV for the first time.
Two beams of particles travelling a whisker below the speed of light are sent flying in opposite directions through 16.7 miles of circular tunnels beneath the Swiss-French border.
But the beam energy has only now been ramped up to its operating level of 13 TeV, almost twice the power used to uncover the Higgs boson two years ago.
The LHC team astounded the world with the discovery of the elementary particle that gives other particles mass, which had eluded detection for nearly 50 years.
With the ability to tap into higher energy, the scientists hope to explore mysterious realms of ''new physics'' that could yield evidence of hidden extra dimensions and dark matter.
Dark matter is the invisible, undetectable ''stuff'' that makes up 84% of material in the universe and binds galaxies together, yet whose nature is unknown.
Protons race around the LHC beam tunnels at three metres per second below the speed of light.
The energy released when they collide is used to spark the creation of new particles.
Albert Einstein's famous equation E=MC2 showed that energy and mass are interchangeable. Upping the energy levels at the LHC increases the chances of some of it being converted to previously undetected, heavier particles - possibly including dark matter.
The particle collisions take place in four detectors arranged around the beam ring known as Atlas, CMS, Alice and LHCb.
Atlas team leader Professor David Charlton, from the University of Birmingham, 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, LHC scientists hope to create 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.
Supersymmetry seeks to fill gaps in the Standard Model, the all-encompassing blueprint of particles and forces in the universe that has been in place since the 1970s.