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Hunting the Higgs

CAMBRIDGE – Fifty years ago, particle physicists faced an unexpected challenge. Their best mathematical models could account for some of the natural forces that explain the structure and behavior of matter at a fundamental level, such as electromagnetism and the weak nuclear force responsible for radioactive decay. But the models worked only if the particles inside of atoms had no mass. How could huge conglomerations of such particles – proteins, people, planets – behave as they do if their constituent parts weighed nothing at all?

Some physicists invented a clever workaround. They suggested that a type of particle exists that had never been detected; it was eventually named in honor of the British physicist Peter Higgs. For a half-century, physicists searched for the elusive “Higgs particle.” Now, following research conducted at CERN, the sprawling particle-physics laboratory near Geneva, the hunt may soon be over.

At first blush, the idea behind the Higgs particle sounds outlandish. Higgs and his colleagues suggested that every elementary particle really is massless, just as the mathematical models require, and hence all particles would ordinarily zip around at the speed of light. But suppose that everything around us – every single particle in the universe – is immersed in a huge, unseen vat of Higgs particles. Whenever most kinds of particles move from point A to point B, they continually bump into Higgs particles, slowing their motion. When we observe them, they appear to lumber along like holiday shoppers in a crowded store. From their slow motion, we infer that they have mass.

While a 50-year search for a hypothetical particle reminiscent of a bizarre fairytale might seem quixotic, the Higgs particle stands at the center of the “Standard Model” of particle physics. Every experimental test of the model so far has matched theoretical expectations. In some striking examples, the agreement between prediction and measurement has stretched out to twelve decimal places, making the Standard Model the most accurate scientific theory in human history. The model successfully accounts for three of the four basic forces of nature; only gravity remains beyond its purview.