Two circulating beams produced the first particle collisions in the world's biggest atom smasher, the Large Hadron Collider (LHC), three days after its restart, scientists announced.
In a statement, the European Organisation for Nuclear Research (Cern) said two beams circulating simultaneously led to collisions at all four detection points during the afternoon and evening.
"It's a great achievement to have come this far in so short a time," said Cern director general Rolf Heuer. "But we need to keep a sense of perspective. There's still much to do before we can start the LHC physics programme."
Cern had declared earlier Monday the re-launch of the €3.9 billion euro collider "an enormous success," after it was out of action for 14 months due to a serious electrical fault.
Scientists are looking to the collider - inside a 27-kilometre tunnel straddling the Franco-Swiss border - to mimic the conditions that followed the Big Bang and help explain the origins of the universe.
"Today the LHC circulated two beams simultaneously for the first time, allowing the operators to test the synchronisation of the beams and giving the experiments their first chance to look for proton-proton collisions," Cern said in its statement.
"With just one bunch of particles circulating in each direction, the beams can be made to cross in up to two places in the ring," it explained.
The first collision was picked up at 2.44 p.m. by the Atlas detector, beneath the Swiss town of Meyrin, one of several laid out along the route of the world's most powerful physics experiment.
Smash-ups then followed at the three other detectors, known as CMS, Alice and LHCb.
"It was standing-room-only in the Alice control room and cheers erupted with the first collisions," said Alice spokesperson Jurgen Schukraft. "This is simply tremendous."
"The tracks we're seeing are beautiful," added LHCb spokes-person Andrei Golutvin, quoted in the Cern statement. "We're all ready for serious data taking in a few days time." Earlier in the day, scientists injected the first sub-atomic particles back into the collider, then got particle beams circulating within the accelerator.
The LHC has an operating life of up to 15 years, and the collisions that it produces should generate masses of data that could unlock mysteries about the creation of the universe and the fundamental nature of matter.
Scientists want to get the collider running at 1.2 teraelectronvolts or 1.2 trillion electronvolts by year's end - with one teraelectronvolt equal to the energy of a flying mosquito, said a Cern spokeswoman.
That would match the maximum output of what now is the largest functioning collider in the world, at the Fermilab near Chicago in the US.