From the nature of the Higgs boson to dark matter: at CERN in Geneva, LHC is ready to restart

From the nature of the Higgs boson to dark matter

He made us identify the Higgs boson experimentally, half a century after the theoretical prediction of its existence. He broke all energy records, reaching an incredible 13 TeraelettronVolt (TeV). His observations allowed, alternatively, to confirm or deny the current laws of physics. Altogether he has discovered over 60 new particles, including four tetraquarks and one pentaquark, exotic entities that we still know very little about. But the Large Hadron Collider (Lhc), the enormous particle accelerator (the largest in the world, to be precise) at CERN in Geneva, is far from paying.

Now, after three years of restyling, it is back to work, even more powerful than before. On February 9, Linac4 was finally turned on, a new 86-meter-long section of the accelerator, whose construction had been completed in 2017 and which replaces its predecessor, Linac2. The start of Linac4, as reported at CERN, officially marks the start of the countdown for the third round of Lhc experiments, the so-called Lhc Run 3. Let's see what it is and what we hope to discover.

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How Lhc works Basically Lhc is a huge "bumper car" for particles heavy (typically protons), circular in shape. Specifically, the protons are produced outside the circumference and are then "injected" into it via a linear accelerator (the Linac machines, to be precise), which increases their energy. Linac4 accelerates negative hydrogen ions (H -, ie a hydrogen atom with an additional electron) to bring them to an energy of about 160 MegaelectronVolts (MeV).

The particle acceleration mechanism is quite complex and is based on radiofrequency cavities that positively and negatively charge (alternately) cylindrical conductors. When the ions enter the cavity, the conductors behind them "push" them and those in front of them "pull" them, exploiting respectively the repulsion and electromagnetic attraction and thus increasing their energy. At this point, the ions enter another machine, the Proton Synchroton Booster, which deprives them of two electrons, effectively transforming them into accelerated protons, and finally injects them into the circular part of Lhc, where they begin to spin, accelerating more and more. , and to collide. It is precisely by studying the characteristics of these collisions that physicists are able to infer information about the nature of particles and the laws of physics.

"Despite all the difficulties due to the pandemic, we have completed all the objectives we had set ourselves to achieve during these three years of shutdown - explained Lothar Bauerdick, program manager of Cms, one of the Lhc experiments - and we can't wait to start collecting data again, with a new and updated detector, and with particles at even greater energies. All this should allow us to make new discoveries in the coming years, and to refine what we already know ".

The news at CERN The improvements, in particular, should serve to understand even more in detail the nature of the boson of Higgs, shed light on the mysteries of dark matter and energy and define the limits of the Standard Model, the currently most reliable and precise theory to explain the behavior of elementary particles and fundamental forces known to date.

"I new experiments - Phil Allport, of the University of Birmingham, told New Scientist - will help us shed light on what happens at very high energies, which could explain the phenomena that occurred in the first moments of the Universe's life and those not fully described by the Model Standard ". Among these, for example, there is the so-called hierarchy problem, that is, the apparently inexplicable difference between the mass of the Higgs boson and that of other fundamental particles. “We need to extend the Standard Particle Model to account for these inexplicable phenomena. And we know that to extend the Standard Model we need to increase the energy of collisions, "the teacher noted. In this sense, one can think of a particle accelerator as a huge microscope: the greater the energy that can be reached, the greater the "magnification" with which one can observe what happens on microscopic scales.

By the way, the Lhc update is not the last. Another one is already planned, scheduled for 2024, which will make the particle beams even tighter and more precise, thus increasing the number of collisions. In recent experiments, physicists had observed about 40 collisions each time two proton beams crossed each other. In the next few, they hope that the figure will reach 250. At that point, a name change will also be necessary: ​​Lhc will officially become Hllhc, or High Luminosity Large Hadron Collider. And probably another story will begin.