10 years of Higgs boson | How the particle could unlock new physics beyond the standard model

In the past decade, measurements of the properties of the Higgs boson have confirmed the predictions of the standard model of particle physics. But it has also raised questions about the limitations of this model, such as whether there’s a more fundamental theory of nature.

Ten years ago, scientists announced the discovery of the Higgs boson, which helps explain why elementary particles (the smallest building blocks of nature) have mass. For particle physicists, this was the end of a decades-long and hugely difficult journey — and arguably the most important result in the history of the field. But this end also marked the beginning of a new era of experimental physics.

In the past 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 it has also raised questions about the limitations of this model, such as whether there’s a more fundamental theory of nature.

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 elementary particles mass. This theory suggests particle masses are a consequence of elementary particles interacting with a field, dubbed the Higgs field. And according to the same model, such a field should also give rise to a Higgs particle — meaning if the Higgs boson wasn’t there, this would ultimately falsify the entire theory.

But it soon became clear that discovering this particle would be challenging. When three theoretical physicists calculated the properties of a Higgs boson, they concluded with an apology. “We apologise to experimentalists for having no idea what is the mass of the Higgs boson... and for not being sure of its couplings to other particles.... For these reasons, we do not want to encourage big experimental searches for the Higgs boson.”

It took until 1989 for the first experiment with a serious chance of discovering the Higgs boson to begin its search. The idea was to smash particles together with such high energy that a Higgs particle could be created in a 27km long tunnel at CERN in Geneva, Switzerland — the largest electron-positron (a positron is almost identical to an electron but has opposite charge) collider ever built. It ran for 11 years, but its maximum energy turned out to be just 5% too low to produce the Higgs boson.

Meanwhile, the most ambitious American collider in history, the Tevatron, had started taking data at Fermilab, close to Chicago. The Tevatron collided protons (which, along with neutrons, make up the atomic nucleus) and antiprotons (nearly identical to protons but with opposite charge) with an energy five times higher than what was achieved in Geneva – surely, enough to make the Higgs. But proton-antiproton collisions produce a lot of debris, making it much harder to extract the signal from the data. In 2011, the Tevatron ceased operations – the Higgs boson escaped detection again.

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