Brief History of the Higgs Mechanism

A Brief History of the Higgs Mechanism: The scientific work behind the Higgs boson

The electroweak theory, which unifies the electromagnetic and weak interactions of elementary particles, has, since 1970, received experimental support to a precision unprecedented in the history of science. This unification involves a close relationship between the massless photon, which carries the long-range electromagnetic force, and the W and Z vector bosons, which carry the short-range weak force and must therefore be very massive. Prior to the invention of the Higgs mechanism, it was not known how to formulate a consistent relativistic field theory with a local symmetry which could contain both massless and massive force carriers.

In 1962, Goldstone’s theorem had shown that spontaneous breaking of symmetry in a relativistic field theory results in massless spin-zero bosons, which are excluded experimentally. In a paper published in Physics Letters on 15 September 1964 (received on 27 July 1964), Peter Higgs showed that Goldstone bosons need not occur when a local symmetry is spontaneously broken in a relativistic theory(1). Instead, the Goldstone mode provides the third polarisation of a massive vector field. The other mode of the original scalar doublet remains as a massive spin-zero particle – the Higgs boson.

Higgs wrote a second short paper describing what came to be called “the Higgs model” and submitted it to Physics Letters, but it was rejected on the grounds that it did not warrant rapid publication. Higgs revised the paper and submitted it to Physical Review Letters, where it was accepted (2), but the referee, who turned out to be Yoichiro Nambu, asked Higgs to comment on the relation of his work to that of Francois Englert and Robert Brout, which was published in Physical Review Letters on 31 August 1964, the same day his paper was received. Higgs had been unaware of their work, because the Brussels group did not send preprints to Edinburgh. Higgs’ revised paper drew attention to the possibility of a massive spin-zero boson in its final paragraph. During October 1964, Higgs had discussions with Gerald Guralnik, Carl Hagen and Tom Kibble, who had discovered how the mass of non-interacting vector bosons can be generated by the Anderson mechanism (4).

The previous year, Philip Anderson had pointed out that, in a superconductor where the local gauge symmetry is broken spontaneously, the Goldstone (plasmon) mode becomes massive due to the gauge field interaction, whereas the electromagnetic modes are massive (Meissner effect) despite the gauge invariance5. However, he did not discuss any relativistic model and so, since Lorentz invariance was a crucial ingredient of the Goldstone theorem, he did not demonstrate that it could be evaded. In Higgs’ second 1964 paper (2) he referred to Anderson’s work in a way which implied that Anderson knew about the non-relativistic counterpart of the Higgs boson. In fact, Anderson didn’t and it was not until 1981 that an unexpected feature of the Raman spectrum of NbSe2 was understood to be due to “a massive collective mode which exists in all superconductors – the oscillation of the amplitude of the superconducting gap” (6), the only Higgs boson so far to be discovered experimentally.

The search for the Higgs boson has become a major objective of experimental particle physics. Although the best fit to all the electroweak precision measurements gives its mass between 52 and 110 GeV, it has been excluded below 114 GeV. Its mass cannot exceed 1 TeV if the electroweak theory itself is to remain valid up to this energy scale, precisely the range that is being explored by CERN’s Large Hadron Collider. Higgs’ work has been a crucial step towards a unified theory of the forces of Nature and is the basis for an experimental programme which is guaranteed to discover new physics.

Researchers at the Large Hadron Collider announced yesterday that they may well have found the long-sought after Higgs boson, sometimes called the "God particle," which is the final missing part of the Standard Model of particle physics. Theoretical physicist Peter Higgs predicted the existence of the particle back in the 1960's, but he was so far ahead of the technology that it took nearly half a century to actually get the first glimpse of the thing ... except, of course, for the glimpses that are all around us, if Higgs is right.

Peter Higgs awaits word from CERN on the potential discovery of the Higgs boson
Source: CERN

Because if he is right, then evidence of the Higgs boson is everywhere. See, the reason Peter Higgs needed to propose his theory was that the physical theories he had to work with at the time had one major flaw: they didn't explain why there was any stuff in the universe.
That's right. The very best scientific explanations that physicists could come up with had a gaping hole in the middle of them. They depicted a universe that was so elegant and finely tuned that ... it shouldn't actually have anything in it. For example, the gauge bosons that mediate the weak nuclear force (called the W boson and Z boson) should, according to theory, have absolutely no mass. But they do have mass! So Peter Higgs set out to try to explain why and how matter itself could exist, in a way that was fully consistent with all of the known laws of physics.

The result was to propose a field in empty space, a field that permeates all of space, called the Higgs field, which has the right properties needed to give mass to these particles ... and, in turn, to cause the mass of all the rest of the universe, as well.
And, in quantum physics, fields can also be expressed as particles (one of the many weird things about quantum physics), so the resulting particle was called the Higgs boson. (It was called a boson because it had a spin of 0. If it had a spin of one-half it would have been a Higgs fermion, but then it wouldn't have been able to do what it needed to do!)
As with most things in physics, that's an over-simplification of the story. It sounds like Higgs came up with the whole idea out of nowhere, and he didn't. The ideas were built on the work of others and many others came upon similar ideas at almost exactly the same time, so even calling the resulting fields and particles "Higgs" can be a controversial thing to do. Still, the fact is that he was a key player in creating the model which, over the last almost-fifty years, has been refined to explain how the symmetries of the universe are broken in the precise way that we need in order to get matter.
And that model may be about to be confirmed by experimental evidence!
Congrats to you, Peter Higgs ... and to all the other players in this drama that is theoretical physics!