Boson W, Dark Matter: The New Challenges of the LHC, the World’s Most Powerful Particle Accelerator

Buried 100 meters underground near Geneva, the monster awoke. The world’s largest and most powerful particle accelerator, the Large Hadron Collider (LHC), managed by CERN, the European Organization for Nuclear Research, was successfully restarted at the end of April. For three years, scientists and engineers have worked to perfect this technological behemoth to increase its performance and detection accuracy. The new version of the LHC is now operational and offers hope for new discoveries and even, some say, new physics.

On April 22, the LHC gradually resumed its activities

This ring, 27 kilometers in circumference, made up of thousands of superconducting magnets, is a feat of engineering and science. In the accelerator, two beams of particles travel in opposite directions at very high energy and almost the speed of light before colliding with each other. These are protons (particles of the atomic nucleus) that collide head-on at colossal speeds to reveal the elemental components of our world. With the ultimate goal of unraveling the mysteries of matter.

Since its restart on April 22, the LHC has gradually resumed activity: a small number of protons have been circulating in opposite directions along the huge circular tunnel with a low collision rate, but their power will increase. “The high-intensity, high-energy collisions will happen in a few months,” explains Rhodri Jones, head of the radiation department at CERN. When the machine restarts, teams will increase the intensity of the proton beams to achieve record-breaking energy collisions.

12,000 scientists are involved in the LHC work

“The work has also improved the accuracy of the four LHC detectors,” says Roberto Salerno, researcher at the CNRS associated with Cern, professor at the École Polytechnique. “With this we achieve more particle collisions and with that collect a much larger amount of data. » The approximately 12,000 scientists could then participate in the work of the LHC Study the Higgs boson in detail, the physicist rejoices . We have yet to define exactly all of its properties and its connections with other particles, but also to figure out how it gets its own mass.”

One of the biggest shortcomings of the Standard Model is that it cannot explain dark matter, an invisible and theoretical mass that makes up the universe, and the dark energy it produces, which is supposed to explain the acceleration of the expansion of the universe. Roberto Salerno

In 2012, the Collider experiments, which started in 2008, made it possible to prove the existence of the Higgs boson. Nicknamed the “God Particle,” this unique particle gives all other particles their mass, making it one of the cornerstones of the Standard Model of particle physics. A theory formulated in the 1960s that explains all observable phenomena on the infinitesimal scale consistent with quantum mechanics. It applies to all known particles, as well as to the three interactions that act on this scale: electromagnetic, strong, and weak. But what about gravity, which itself comes from the infinitely large, i.e. from Einstein’s general theory of relativity?

Until the next LHC shutdown, scheduled for 2026-2028, physicists hope to make progress in the search for this gravitational phenomenon and to test the Standard Model, recently rocked by several experiments. For example, the W boson discovered in 1983, whose mass turned out to be much heavier than theory had previously predicted in a recent experiment. “All these anomalies could be explained by a new force” which would be added to the four fundamental forces that govern the universe (strong, weak, electromagnetic and gravitational), explains University of Cambridge physicist Harry Cliff.

Check Einstein’s theory

However, one of the major challenges for the LHC would be the discovery of a hypothetical particle representing an invisible form of matter called “dark matter” that is insensitive to electromagnetic forces. If we couldn’t discover it, we would have to check Einstein’s theory. “One of the major shortcomings of the Standard Model is that it cannot explain dark matter, an invisible and theoretical mass that makes up the universe, and the dark energy it produces, which is designed to explain the acceleration in the expansion of the universe.” , explains Roberto Salerno. Dark matter, which makes up more than a quarter of the universe, remains one of the greatest mysteries in physics. According to Rende Steerenberg, operations manager at CERN, the work will be carried out at the LHC should “significantly increase the probability of new discoveries in this field”.

To achieve this, researchers can attempt to create dark matter by performing proton-on-proton collisions. “But since this dark matter is by definition unobservable, we would have to couple it with other particles to infer its existence from the deviations from the predicted results it produces,” explains Roberto Salerno . Another method would be to discover it through the decay of known particles like the Higgs boson. A bridge could finally connect the physics of the infinitely small with that of the infinitely large.

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