By Don Lincoln, Fermilab
The discovery of Higgs boson was announced on July 4, 2012. Nobel Prize winner Leon Lederman had written a book about the Higgs boson with the provocative title The God Particle, and the media had made erroneous connections between science and religion, annoying both scientists and theologians. So, what really is the Higgs boson? What does it do? Why is it interesting and important?
Unifying Weak Nuclear Force
The story of the Higgs boson and the Higgs field begins in the early 1960s. The scientists of the time knew about four forces: gravity, electromagnetism, the strong nuclear force, and the weak nuclear force.
We know what gravity is. Electromagnetism is responsible for electricity and magnetism, and also chemistry and how light works. The strong nuclear force ties the protons and neutrons together in the center of atoms, as well as a few other things, and the weak nuclear force causes some sorts of radioactive decay, most notably the emission of neutrinos.
In the early 1960s, researchers discovered that they could come up with equations that unified the weak nuclear force and electromagnetism. Unification has a specific meaning in physics. It basically means that two things that seemed to be different came from a single cause.
Electroweak Force
A historical example was when Isaac Newton realized that the motion of planets across the sky and the reason that Cheerios fall when a baby drops them from their highchair come from a single principle called gravity. Even his name for it, which is the Theory of Universal Gravity, makes it clear that he had unified two ideas. A more modern unification was in the 1870s when James Clerk Maxwell unified electricity and magnetism into a combined theory called electromagnetism.
And, in the 1960s, scientists found a way to unify electromagnetism and the weak nuclear force into a combined force called the electroweak force.
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Problem with Electroweak Theory
However, there was a problem with the electroweak unification. It predicted four particles that carried the electroweak force. Furthermore, it predicted that the four particles all had zero mass. That last one is a big deal because a force-carrying particle with zero mass means the force has an infinite range.
The most familiar such particle is the photon, which transmits the force of electromagnetism, and because we can see distant stars, we know that the range of the photon is infinite.
And yet the weak force certainly doesn’t have infinite range. In fact, even at the time, researchers knew that the weak force only extended over a distance about one one-thousandth the size of a proton.
A Dead End?
So, this could well have been the death knell of electroweak theory. It predicted that the weak force should have infinite range, just like electromagnetism. In contrast, experiments showed that the weak force had a very short range. And (this is important) if the weak force had a short range, the force-carrying particle for the weak force couldn’t be massless. It had to be massive.
And that’s where the Higgs field and boson come in.
Higgs Theory
In 1964, Peter Higgs wrote a paper that hoped to solve the problem. He proposed that there was an energy field that permeated the entire universe. This energy field is called the Higgs field. This energy field would interact with some particles and give them mass; other particles would ignore the field, and those particles would be massless.
When this Higgs field idea was applied to the electroweak theory, the outcome was that one particle didn’t interact with the Higgs field and that was the massless photon. Another outcome was that there was a heavy and electrically neutral particle that we now call the Z boson. That particle transmitted the weak nuclear force. There were also two massive electrically charged particles, one negative and one positive, that also transmitted the weak force. These are now called the W-plus and W-minus bosons. We often just clump them together and call them the W boson and ignore the fact that there are two particles with opposite charge.
Another prediction of the Higgs theory was that there exists yet another particle called the Higgs boson. That was the particle that was discovered in 2012.
Higgs Field
Other than the one of Peter Higgs, there were two more papers with different facets of the same idea published in the same year. Robert Brout and François Englert wrote one, while Gerald Guralnik, Carl Hagen, and Tom Kibble wrote another.
However, mostly as a historical accident, scientists combine the ideas of all six physicists and call it the Higgs field. If one really needs a reason why Higgs was singled out, it was in his paper that he noted that if the Higgs energy field idea was right, then there should also be a particle that wasn’t discovered in the 1960s called the Higgs boson.
While the announcement in 2012 was about the Higgs boson, it’s the Higgs field that gives mass to particles. Some particles interact with the field and get mass. The Higgs boson is just a vibration of the field, like a wave on a guitar string. In that analogy, the string is the Higgs field and the vibration is the boson.
Common Questions about Higgs Boson and Higgs Field
In the early 1960s, the scientists of the time knew about four forces: gravity, electromagnetism, the strong nuclear force, and the weak nuclear force. Electromagnetism is responsible for electricity and magnetism, and also chemistry and how light works. The strong nuclear force ties the protons and neutrons together in the center of atoms, as well as a few other things, and the weak nuclear force causes some sorts of radioactive decay, most notably the emission of neutrinos.
in the 1960s, scientists found a way to unify electromagnetism and the weak nuclear force into a combined force called the electroweak force.
In 1964, Peter Higgs wrote a paper in which he proposed that there was an energy field that permeated the entire universe. This energy field is called the Higgs field. This energy field would interact with some particles and give them mass; other particles would ignore the field, and those particles would be massless.
