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← Higgs boson hunters scent their elusive quarry at the LHC

TuftedPuffin's Avatar Jump to comment 10 by TuftedPuffin

Comment 5 by Steve Zara :

I can figure out a lot of physics, even though I was not formally trained as a physicist. Relativity? No problem! Black holes? Piece of cake! Even quantum mechanics is really not that hard. It's strange, but not hard. But when it comes to the Higgs Boson, I get utterly lost. I can find no simple explanation of what it's all about that doesn't reduce things to silliness. I know that superconductivity is involved somewhere, and something called the Goldstone Boson, but that's it.

If anyone can point me at a relatively straightforward explanation of what the Higgs Mechanism is all about, I would be very grateful, if such a thing is possible.

Ok, first, while people will say that superconductivity is involved, don't expect this to be helpful. Understanding it via an analogy to superconductivity requires you to be very familiar with superconductivity. It's an analogy designed for physicists to talk to other types of physicists, not laymen.

Goldstone Bosons are more relevant, but still a bit hard to explain, and not that necessary if you just want the gist of what the Higgs is about.

Basically: What we call particles are fluctuations in fields. Each individual particle is a particularly cohesive packet of waves in the corresponding field (a soliton if you've heard the term).

What we call mass is something that happens in the middle of a particle's trajectory and makes the particle's path have a nontrivial relationship to its energy. A massless particle will go at the speed of light no matter what, but a massive particle will travel along and have what might very loosely be called "mass events" that make it take longer, with the lengthening of the path depending on the particle's energy.

By default, these "mass events" are just shorthand for the particle "actually" having some mass. However, most of the fields of the Standard Model (in particular, all force-carrying particles and pretty much every matter particle) cannot have this sort of straightforward mass. The reason why is complicated, but one way to think of it is that these fields all can be viewed in different ways, like the different frames of relativity. If they had a mass, their physics would be different depending on which "frame" they were in.

The solution is to add the Higgs field. Basically, make those "mass events" situations where the particle actually interacts with another field, called the Higgs. Because the Higgs is a field rather than just a number, it can vary between "frames" and cancel out the trouble that a simple number for the mass would cause.

In order for this to work, the Higgs needs a vacuum value: a baseline Higgs field above zero. This value determines the masses of various particles. It's reasonably well determined, the only reason it isn't fixed up to umpteen decimal places is because the other particles aren't either, since their masses were found by collider experiments, and its value is determined by consistency with these masses.

Remember what I said at the beginning about particles and fields? The Higgs field has a certain background value, and the Higgs particle is a fluctuation around this value, like a wave on a lake. The Higgs interacts with itself, so the vacuum Higgs field gives a mass to the Higgs particle as well. This mass isn't as strongly fixed as the Higgs field value itself because it isn't limited by the same consistency arguments. The particle is what the LHC is looking for.

As for why the large range? The Standard Model restricts the Higgs mass to a fairly low value, unless something exotic is going on. But we're pretty sure the Standard Model isn't the whole story. Supersymmetry adds lots of new particles, and these change the consistency conditions that limit the Higgs mass. Different versions of Supersymmetry propose different Higgs masses in continuous ranges. So in order to find out what sort of Supersymmetry we have we need to scan lots of possible mass values to find the Higgs.

As for Rtambree's question: masses aren't one of the things that got predicted to umpteen decimal places. The super-accurate predictions are from Quantum Electrodynamics, a restricted version of Quantum Field Theory that has a much more limited scope (basically, just Electrons and Photons). Once you go past that you're in a land where calculations become much more difficult.

Sat, 10 Dec 2011 22:50:57 UTC | #897653