The Higgs Boson: Finding the Particle That Gives Matter Its Mass

On July 4, 2012, thousands of scientists around the world cheered, cried, and hugged each other. After nearly 50 years of searching, they had found one of the universe's best-kept secrets — a tiny particle called the HIGGS BOSON. This discovery answered one of physics' biggest questions: why do things have mass at all? Without the Higgs boson, no stars, no planets, no people — nothing solid — could exist.

By the end of this lesson you will: - Explain what a particle is and give examples - Understand the difference between mass and weight - Describe the Higgs field and what the Higgs boson does - Explain how scientists at CERN discovered the Higgs boson in 2012

Everything you can touch is made of incredibly tiny pieces called ATOMS. But atoms themselves are made of even smaller pieces called PARTICLES. Physicists — scientists who study matter and energy — have discovered many types of particles. Some, like electrons and quarks, make up atoms. Others, like photons, make up light. Particle physics is the science of studying these tiny building blocks of the universe. Key particles to know: Quarks — the smallest known building blocks; they group together to form protons and neutrons inside the atom's nucleus. Electrons — tiny particles orbiting the nucleus that carry electric charge. Photons — particles of light; they have no mass at all. Higgs boson — the particle discovered in 2012 that explains why other particles have mass.

Before we get to the Higgs boson, we need to understand MASS. Mass is the amount of matter in an object — how much stuff it is made of. Mass is measured in kilograms. Weight is the pull of gravity on that mass. On Earth, a bowling ball weighs about 16 pounds. On the Moon — where gravity is much weaker — that same bowling ball would weigh only about 2.7 pounds. But the MASS of the bowling ball stays exactly the same wherever you take it in the universe. So here is the deep question the Higgs boson answers: why do particles have mass in the first place?

Here is the big idea behind the Higgs boson: Physicist Peter Higgs and other scientists proposed in 1964 that an invisible field — now called the HIGGS FIELD — fills every single point in the universe, everywhere, all the time. Think of it like an invisible ocean you cannot see, feel, or smell, but it is always there. When particles move through this field, some interact with it. The more strongly a particle interacts with the Higgs field, the harder it is to speed it up or slow it down — and that resistance to change is what we call MASS. Photons do not interact with the Higgs field at all, so they have zero mass and travel at the speed of light. Electrons interact a little, so they have a small mass. Top quarks interact very strongly, so they have a large mass. The Higgs boson itself is a tiny ripple in the Higgs field — like a wave on the surface of that invisible ocean.

Scientists could not find the Higgs boson by looking — it is far too tiny. They had to build a machine powerful enough to create one. At CERN, a science organization near Geneva, Switzerland, physicists built the world's largest machine: the Large Hadron Collider, or LHC. It is a circular tunnel 27 kilometers (17 miles) around, buried 100 meters underground. Inside, two streams of protons are accelerated to 99.9999991 percent of the speed of light and then smashed together. When protons collide at those energies, they break apart — and for a tiny fraction of a second, new particles appear, including the Higgs boson. But the Higgs boson vanishes almost instantly after it is created. Scientists analyzed over 600 trillion proton collisions before they had enough data to be certain they had found it. On July 4, 2012, two independent teams — called ATLAS and CMS — both announced they had detected the Higgs boson. In 2013, Peter Higgs won the Nobel Prize in Physics.