The largest physics experiment in the world is back in service: the LHC particle accelerator, near Geneva, is restarting. It had been shut down for three years to be improved, and here it is again: on April 22, CERN’s large collider, the largest in the world, was reignited. It is in the testing phase until this summer. And then he will explore the secrets of matter for four years.
The collider smashes particles against each other to break them, and discover new ones. It doesn’t sound very high tech, put like that, but that’s exactly what happens in the LHC. This collider is an enormous ring, 27 kilometers long, buried 100 meters underground at the Franco-Swiss border. Inside, physicists propel protons, particles located in the nucleus of atoms. Two beams of protons circulate in the ring, each in one direction, and they collide: the protons explode, and this gives rise to new particles.
This is how physicists have been exploring matter since the 1950s. They have gradually discovered 17 particles that make up all the matter in the universe and describe all of its reactions. The last particle discovered arose precisely at CERN, in 2012, it was the only particle that was missing: the famous Higgs boson.
So what will the LHC be looking for now? He goes looking for the unknown. Because physicists know that their 17-particle model, while complete in itself, is not the end of the story. First, it doesn’t include gravitation: it doesn’t talk about the force that keeps our feet on Earth. But it must play a role, even at the particle scale. Because there are still many other mysteries, other questions… In particular dark matter: it is a matter whose existence we suspect by looking at space: stars rotate too quickly in galaxies and that suggests that there is a mass, a particle, which is there but which we cannot see. The LHC will therefore track it down…
To do this, it needs more power, hence the work carried out over three years to increase the energy of the proton beam. And that’s it, the energy record has already been beaten, Monday, three days after the restart of the accelerator. A world record, greeted with a round of applause in the CERN control room. Now we just have to wait a few weeks before the collisions start.