Beams of protons are circulating in both directions around the Large Hadron Collider (LHC) for the first time after a 14-month shutdown for major repairs.

CERN scientists said that the achievement, made this morning, brings the £5 billion “Big Bang machine” closer to full operation and sets the stage for it to start smashing particles within weeks.

Detectors around the LHC’s 27km (17 mile) ring have already started to pinpoint traces of collisions between particles in the beams and equipment, showing that they are in good working order. Engineers may now bring the two beams together in the next few days to stage small collisions to help scientists to calibrate the detectors, with higher-intensity collisions scheduled before Christmas. High-energy collisions for new physics are then expected in January.

The LHC was retarted on Friday. Steve Myers, CERN’s director of accelerators and technology, said that the first days of resumed operations had been an “enormous success”. “We have two beams circulating simultaneously in the LHC,” he said. “All this bodes very well for the detectors and the project that is in front of us, and will surely lead to new exciting physics discoveries.”

The beams are at low intensity, meaning that they contain fewer protons than they would when the accelerator is fully operational. This is to keep damage to a minimum in the event of an accident.

Dr Myers said that the machine’s safety features will be tested over the next few days, when some collisions may be attempted at low intensity. “When we’ve done all that and ensured everything is safe, we’ll increase the intensity, the number of protons in each beam,” he said.

Engineers will then decide whether to start high-intensity collisions at the accelerator’s current energy of 450 gigaelectronvolts (GeV), or to increase the energy to 1.2 teraelectronvolts (TeV) before pressing ahead with collisions. At 1.2 TeV, the LHC would break the energy record for particle accelerators, which stands at 1 TeV and is held by the Tevatron at Fermilab near Chicago.

Scientists working on the LHC’s detectors said that they were delighted with the progress. “It’s the end of a phase and we’re entering another phase,” said Fabiola Gianotti, of the Atlas experiment, aimed at learning about the basic forces that have shaped our Universe since the beginning of time. “It’s the end of 20 years of effort to build the machine and detectors of unprecedented complexity. We’re getting to a fantastic new era of physics and discovery that I hope will change the physics textbooks. It really is a big emotion.”

Tejinder Virdee, of the Compact Muon Solenoid experiment, which aims to find new particles, detect mini black holes and what constitutes dark matter, said: “Let me first thank the machine, it’s performing exceedingly well and that augurs very well for the future. This weekend was an important step, it was very successful and very exciting dare I say it for the experiment.

“The second half of this incredible journey we are all on, that probably has another decade or so to run to extract new physics from this machine.”

Andrei Golutvin, of the LHCb experiment, which aims to study the beauty, or “b” quark, said: “We hope that Nature will be kind to us and open its secrets.”

Jurgen Schukraft, of the Alice experiment — the acronym for A Large Ion Collider Experiment — said: “If we’d done half of what we’ve done in the last three days it would be a great success. We have already seen collisions between one beam and our equipment.”

CERN will increase the energy of the LHC still further next year, Dr Myers said, to allow scientists to start investigating new physics. The possible advances include the discovery of the Higgs boson — the elusive “God particle” — thought to give matter its mass.

“Next year we will start putting up the energy to 3.5 TeV per beam, and do physics for several months,” Dr Myers said. “Then we’ll consider putting up the energy to 5TeV per beam in the second half of next year.”

Rolf Heuer, CERN’s director-general, said that it was impossible to predict what the LHC would find first. “Give me a crystal ball and I’d know. I do not know what Nature has for us,” he said.

Dr Gianotti said: “We are doing research, and research is research because we do not know what we’re going to find.”

The LHC’s maximum energy of 7 TeV will not be achieved without shutting the collider down for extensive modifications, Dr Heuer said. There were no plans to increase energy to that level until 2011 at the earliest.

Nine days after the machine was switched on last September, a connection between two magnets failed, tearing a hole in the collider and causing a huge leak of the liquid helium that cools its superconducting magnets.

Engineers took more than a year to investigate and repair the fault, check the rest of the accelerator for similar problems, replace faulty magnets and install new safety devices to prevent a repeat.

Times Recommends

• The Olympics: you need brass to go for gold
• The new must-have accessory: 3-D specs
• Does Dame Helen Mirren need a Face Lift?