LHC smashes energy record with test collisions

A new record has been set by the Large Hadron Collider: its latest trials have smashed atoms with vastly more energy than ever before.

On Wednesday night, two opposing beams of protons were steered into each other at the four collision points spaced around the LHC's tunnel.

The energy of the collisions was 13 trillion electronvolts - dwarfing the eight trillion reached during the LHC's first run, which ended in early 2013.

"Physics collisions" commence in June.

At that point, the beams will contain many more "bunches" of protons: up to 2,800 instead of the one or two currently circulating. And the various experiments will be in full swing, with every possible detector working to try and sniff out all the exotic, unprecedented particles of debris that fly out of proton collisions at these new energies.

For now, however, the collisions are part of the gradual testing process designed to ensure nothing is missed and nothing goes awry when the LHC goes into that full "collision factory" mode.

"We begin by bringing the beams into collision at 13 TeV (teraelectronvolts), and adjusting their orbits to collide them head-on," said Ronaldus Suykerbuyk from the operations team at Cern - the organisation based near Geneva in Switzerland that runs the LHC.

The huge collider has been through a planned two-year refit, after the conclusion of its first run - which in 2012 produced the first solid evidence for the famous Higgs boson.

So physicists are excited to see the machine winding back up again, although it is an overwhelmingly incremental process.

In early April, after a slight delay, twin proton beams circulated the LHC's 27km ring, 30 storeys below the Swiss-French border, for the first time in two years. This was at a much lower, preliminary energy; five days later the energy reached 6.5 TeV per beam for the first time.

The first collisions followed in early May - again, at a lower, safer energy to begin with. Thursday's collisions are in new territory.

Prof David Newbold, from the University of Bristol, works on the CMS experiment. He said the new energies present new technical challenges.

"When you accelerate the beams they actually get quite a lot smaller - so the act of actually getting them to collide inside the detectors is really quite an important technical step," Prof Newbold told BBC News.

"13 TeV is a new regime - nobody's been here before."

Now that collisions are underway, Prof Newbold explained, the engineers in charge of the beams can start to pump in more and more protons.

"The special thing about LHC is not just the energy we can collide the beams at, it's also the number of collisions per second, which is also higher than any other accelerator in history.

"The reason for that is - like the Higgs boson last time - what we're principally looking for is incredibly rare decay particles. And the more collisions you have per second, the more chance you have of finding something that's statistically significant."

So the build-up that will now unfold, from one or two bunches of protons to thousands, will make even more history. But these early tests are critical to make sure that the 6.5 TeV beams can be steered onto collision course without damaging any of the detectors, or the massive magnets that steer the protons and accelerate them to very near the speed of light.