Ten years ago, scientists announced the discovery of the Higgs boson, which helps explain why elementary particles (nature’s smallest building blocks) have mass. For particle physicists, this was the end of a decades-long and very difficult journey, and probably the most important outcome in field history. But this end also marked the beginning of a new era of experimental physics.
In the last decade, measurements of the properties of the Higgs boson have confirmed the predictions of the standard model of particle physics (our best theory for particles). But he has also raised questions about the limitations of this model, such as whether there is a more fundamental theory of nature.
The physicist Peter Higgs. wikipedia, CC BY-SA
Physicist Peter Higgs predicted the Higgs boson in a series of papers between 1964 and 1966, as an inevitable consequence of the mechanism responsible for giving mass to elementary particles. This theory suggests that particle masses are a consequence of the interaction of elementary particles with a field, called the Higgs field. And according to the same model, this field should also give rise to a Higgs particle, that is, if the Higgs boson were not there, this would ultimately falsify the whole theory.
But it soon became clear that discovering this particle would be a challenge. When three theoretical physicists calculated the properties of a Higgs boson, they concluded with an apology. “We apologize to the experimentalists for not having any idea what the mass of the Higgs boson is … and for not being sure of its couplings with other particles … For these reasons, we do not want to encourage large experimental searches of the Higgs boson “.
It took until 1989 for the first experiment with a high chance of discovering the Higgs boson to begin his research. The idea was to crush particles with such high energy that a Higgs particle could be created in a 27 km long tunnel at Cern in Geneva, Switzerland: the electron-positron collider (a positron is almost identical to a electron but has opposite charge) larger. never built. It operated for 11 years, but its maximum energy turned out to be only 5% too low to produce the Higgs boson.
Meanwhile, the most ambitious American collider in history, the Tevatron, had begun taking data at Fermilab, near Chicago. The Tevatron collided with protons (which, together with neutrons, form the atomic nucleus) and antiprotons (almost identical to protons but with opposite charges) with an energy five times higher than that achieved in Geneva, probably enough to make the Higgs. But proton-antiproton collisions produce a lot of waste, making it much more difficult to extract the signal from the data. In 2011, the Tevatron ceased operations: the Higgs boson again escaped detection.
In 2010, the Large Hadron Collider (LHC) began colliding protons with seven times more energy than the Tevatron. Finally, on July 4, 2012, two independent experiments at Cern had collected enough data to declare the discovery of the Higgs boson. The following year, Higgs and his collaborator François Englert won the Nobel Prize “for the theoretical discovery of a mechanism that contributes to our understanding of the origin of the mass of subatomic particles.”
That almost sells it short. Without the Higgs boson, the whole theoretical framework describing particle physics at its smallest scales is broken. The elementary particles would be without mass, there would be no atoms, no humans, no solar systems or structure in the universe.
Problems on the horizon
However, the discovery has raised new fundamental questions. Experiments at Cern have continued to probe the Higgs boson. Its properties not only determine the masses of elementary particles, but also their stability. As it stands, the results indicate that our universe is not in a perfectly stable state. In contrast, similar to ice at the melting point, the universe could suddenly experience a rapid “phase transition.” But instead of going from a solid to a liquid, like ice passing into water, this would involve crucially changing the masses and laws of nature in the universe.
The fact that the universe, however, seems stable suggests that something might be missing from the calculations, something we have not yet discovered.
After a three-year hiatus for maintenance and upgrades, collisions at the LHC are now about to resume with unprecedented energy, nearly twice as much as had been used to detect the Higgs boson. This could help us find missing particles that take our universe away from the apparent knife cut between being stable and quickly experiencing a phase transition.
The experiment could also help answer other questions. Could the unique properties of the Higgs boson make it a portal to discover dark matter, the invisible substance that makes up most of the matter in the universe? Like many elementary particles, dark matter is not charged. And the Higgs boson has a unique way of interacting with uncharged matter.
The same unique properties have led physicists to wonder if the Higgs boson might not be a fundamental particle after all. Could there be a new and unknown force beyond the other forces of nature: gravity, electromagnetism, and weak and strong nuclear forces? Perhaps a force that binds hitherto unknown particles into a composite object we call a Higgs boson?
It’s been 10 years since the Higgs was discovered. D-VISIONS / Shutterstock
These theories may help address the controversial results of recent measurements that suggest that some particles do not behave exactly as the standard model suggests they should behave. Therefore, studying the Higgs boson is vital in determining whether there is physics to discover beyond the standard model.
Eventually, the LHC will face the same problem as the Tevatron. Proton collisions are disordered and the energy of their collisions will only get that far. While we have at our disposal the entire arsenal of modern particle physics, including sophisticated detectors, advanced detection methods, and machine learning, there is a limit to what the LHC can achieve.
A future high-energy collider, designed specifically to produce Higgs bosons, would allow us to accurately measure its most important properties, including the interaction of the Higgs boson with other Higgs bosons. This in turn will determine how the Higgs boson interacts with its own field. Therefore, studying this interaction could help us investigate the underlying process that gives masses to particles. Any disagreement between the theoretical prediction and a future measure would be a clear signal that we must invent a new physics.
These measurements will have a profound impact that goes far beyond the physics of the collider, guiding or limiting our understanding of the origin of dark matter, the birth of our universe, and perhaps its final destination.