Inside the Large Hadron Collider
Inside the LHC: 'The Higgs discovery was easy,' says the head of Cern. 'Now the real work starts' © Cern

The Large Hadron Collider will restart its discovery programme early in 2015, after a two-year shutdown during which Cern has almost doubled the operating power of its $8bn atom smasher.

“There is a new buzz about the laboratory and a real sense of anticipation,” says Cern director-general Rolf-Dieter Heuer. “Much work has been carried out on the LHC and it’s effectively a new machine, poised to set us on the path to new discoveries.”

The thousands of scientists who work on the LHC’s multiple experiments hope that the extra energy of its proton-proton collisions will enable them quickly to reveal “new physics” beyond the Standard Model of particles and forces built up over the past half-century. The first run from 2009 to 2012 led to one triumphant discovery: the Higgs boson, which endows mass on other particles and was the last important prediction of the Standard Model to be verified.

Further analysis, carried out during the shutdown, shows the Higgs behaving as a single particle. Physicists were hoping for more complexity – for example, a family of Higgs bosons with slightly different properties – because they know physics has to move beyond the simple Standard Model to explain many phenomena from gravity to the mysterious dark matter and dark energy that pervade the universe.

The LHC’s upgrade from 8TeV to 13TeV (tera-electronvolts are the units used to measure collision energies in particle accelerators) could reveal hints of that sought-after complexity quite quickly next year. “I told the scientists that the Higgs discovery was easy and now the real work starts,” says Heuer. “Does the Higgs boson have brothers and sisters?”

“The discovery of a Higgs boson was just the beginning,” adds his colleague Fabiola Gianotti. “The increase in energy opens the door to a whole new discovery potential.”

The LHC’s detectors picked up 1,400 Higgs particles during the first run. The second run is expected to yield 100,000 for analysis.

The two most discussed prospects for discovery when the LHC resumes are supersymmetry – the theory that all fundamental particles in the Standard Model have a least one heavier partner waiting to be found – and dark matter.

If supersymmetry is correct, the evidence should emerge fairly soon after the restart. The search for the invisible, and so far undetectable, dark matter is likely to take longer.

Meanwhile Cern has begun the search for a new director-general to replace Heuer who will retire at the end of 2015 after seven successful years. The UK has already proposed a candidate: John Womersley, head of the Science and Technology Facilities Council, which funds Britain’s national activities in high energy physics.

Photograph: Cern

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