Buried underground, in an atmosphere of neon, pipes and reinforced concrete that a James Bond villain would not deny, the flashing buttons and the turbines are back in action.

After three years of work to increase its power, the Large Hadron Collider (LHC) at CERN (European Organization for Nuclear Research), the largest particle accelerator in the world, is restarting, pending its XL version.

This Friday around 12 p.m., "two beams of protons (particles from the nucleus of the atom, editor's note) circulated in opposite directions along the 27-kilometer ring", located 100 meters underground at the Franco-Swiss border, near Geneva, CERN said in a statement.

The gigantic structure, looking like a missing link between our daily lives and science fiction, had been on technical shutdown since December 2018 for maintenance and improvement work, in the second longest break in its history.

The experiments at the LHC, started in 2008, notably led to the revolutionary discovery of the Higgs boson, the keystone of the fundamental structure of matter.

A gradual recovery

The principle of the collider is to collide particles at colossal speeds to generate elementary particles, infinitely small.

The recovery will take place gradually: only a small number of protons have circulated for the moment in the two beams, at 450 billion electron volts, a low collision rate but which will increase in power.

"The high-intensity, high-energy collisions will occur in a few months," said Rhodri Jones, head of CERN's beams department, welcoming a "successful" restart.

As the machine resumes service, the teams will increase the energy and intensity of the beams, to conduct collision experiments with a record energy of 13.6 trillion electron volts.

This will allow the four main LHC detectors (ALICE, ATLAS, CMS and LHCb) to receive more particle collisions and therefore to read a much larger mass of data.

CERN physicists will be able to “study the Higgs boson in great detail” and further test the standard model of particle physics, recently shaken by several experiments.

But the new phase of exploration aims above all to establish new physics beyond this model.

With perhaps eventually new particles, such as supersymmetric particles: predicted by theory but never demonstrated, they could convey dark matter, a great unknown in the Universe.

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