PFE029: The Higgs Mechanism Part 2 - How It Acts

Last week, we heard about why we need the Higgs mechanism to fit in with everything else we know about little things. This week we are going to look at "how it interacts with stuff".

Personally I've always been a fan of this

graphic but whatever, it's super confusing. Let's start with the Higgs at the bottom. The line connecting it to itself means that it interacts with itself. The rest of the lines coming out of it means that it interacts with quarks, W and Z bosons [the weak bosons] and some of the leptons [in particular, the electron plus two others]. Notably absent from that list are gluons, photons, and those other leptons [neutrinos].

Okay, what?

It turns out that these are the particles that have mass. Of course, this is what was mentioned last week. Particles that have mass - a resistance to motion - interact with the Higgs. So the Higgs must somehow resist motion. Since the mass of a particle is proportional to how strongly it interacts with the Higgs, it appears that the Higgs itself, somehow, causes a resistance to motion.

Remember that pushing a monster truck is hard even in space with no gravity and no friction - that's because it still has a giant mass.

At this point people usually try to describe the Higgs as something like "sand that we are all moving through that slows us down - the heavier we are, the more we slow down". Of course this is a terrible description. Okay, not terrible, but still misleading.

The problem is that now everyone is thinking about aerodynamics - a frisbee flying in the regular fashion or flopping through this "Higgs sand" all sideways. But of course, that has nothing to do with it. The frisbee interacts with the Higgs field in the same way no matter how its moving.

Let's think of it a different way - in terms of what doesn't interact with the Higgs. Well there are gluons, but no one wants to have to think about those if they don't have to. There are neutrinos, but since the question of their mass is rather complicated and unclear, we'll ignore them too. Luckily, we still have photons or light - something that we are all familiar with!

Light particles don't interact with the Higgs - they may cross paths, but won't even notice it. What evidence of that do we see? They go at the speed of light!

"Wow, thanks there. Light goes at the speed of light? Great one. Now it all makes perfect sense."

Don't think of "the speed of light" as, well, "the speed of light" quite so much - think of it as the universal speed limit. The fastest that anything is allowed to go.

And since photons don't interact with the Higgs, they are always cruising along at a chill 669 million miles per hour.

But everything else [people and cars and toasters are made up of quarks and electrons] travels slower because they keep interacting with the Higgs field so much.

At this point its somewhat important to differentiate between the Higgs field and the Higgs boson. The field exists everywhere. It is here. It is there. It is in a box. It is in a fox. At any time and at any place, any particle that is allowed to interact with it [quarks, airplanes, electrons,... but not photons] does. This constant uniform behavior makes sure that all electrons have the same mass everywhere.

The boson - the particle - associated with all this nonsense, is a result of the fact that the field interacts with itself. A field doesn't have to do this, but because this one does, the Higgs boson itself has a mass.

That's how the Higgs acts.

PFE028: The Higgs Mechanism Part 1 - The Need

Some of you may think that my recent hiatus was due to laziness, forgetfulness, boredness, etc. I have actually been waiting on CERN to write a post on the Higgs - I wanted to wait for it to reach discovery status. It is that time. This is the first in a three part series walking you through the need for the Higgs mechanism, what the Higgs mechanism is like, and the road to discovery.

There have been, recently, a few posts on the internet discussing the Higgs boson, the recent announcement from CERN, and what it all means. While many of them have stuck strictly to the facts many more [by my entirely unscientific count] have taken numerous liberties with said facts. Here at PFE you get the fair and balanced full story.

First, if you haven't already, go take a look at my last post on mass. Done?

Next, what are we talking about? Let's think about some vocabulary.

1. Mass as discussed in this post will be that of inertial mass. Particle physics does not describe how gravity works [yet, we have some ideas though!]. Moreover, the mass of particles in question is so incredibly small that measuring their gravitational effects is overly tricky. As such the Higgs mechanism has nothing to do with gravity.
2. The Standard Model is a collection of ideas put together over the 1960's and the 1970's, but the ideas themselves have been in progress for much longer. It describes everything we know about particle physics and unites three of the four forces [electromagnetic, strong, and weak - but not gravity]. It has been incredibly predictive and people are still working out all of the implications of the theories put together.
3. "The God Particle" is a completely incorrect name often assigned to the Higgs boson. In 1993, Nobel laureate Leon Lederman wrote a book about, among other things, the Higgs boson. Apparently, he wanted to use the phrase "The Goddamn Particle" in the title due to the difficulty in tracking down the particle, but his publisher wouldn't let him. This name has led to a vastly increased media coverage distorting the facts. One popular myth goes along the lines of, "the particle is everywhere and interacts with everything so it is called 'The God Particle'". In fact, it does not interact with everything, and the particle is a consequence of a field that exists everywhere. There are multiple other fields [that which gives rise to light for instance] that exists everywhere.
4. A boson is a classification of particles. All particles are either fermions or bosons. There are a few interesting properties and consequences of each, but they are not relevant for this Higgs discussion.

Before we get into the nitty-gritty details, I should first explain the history of the discovery. In particular, the name Higgs is associated with the man Dr. Peter Higgs

My namesake has some great moves as shown by the blurriness here.

but there were as many as six or more people who came up with the same idea at the same idea. While no Nobel prizes have been awarded on the subject, the Sakurai prize [some nerdy physics prize] was given to Higgs along with Kibble, Guralnik, Hagen, Englert, and Brout.

Enough physics history, that's even duller than physics itself, right?

Where does the Higgs mechanism fit in with everything else? As people were putting together the standard model, they kept awing themselves with the amazing predictions it made: cross sections, scattering angles, branching ratios, electric charges and magnetic moments among many more. But who cares about those? You all just read about mass, it's mass you want to know about. The thing is, there was no real way to sort out the mass of all of these particles. I know what you're thinking: "This great theory doesn't even tell you what mass the particles should have?" It looks like the theory is lost and we are nowhere.

A number of physicists [those six I mentioned above, plus a few others] put together a theory that allowed particles to have masses within the standard model. The problem is not just that particles need to acquire mass, but that they are all different. In a sense, before you add mass into the theory, all of the particles have a sort of symmetry in that they are all massless. But their masses had already been well-measured. Adding in something else to the theory allowed for an elegant means to allow for particles to have masses.

So this seems pretty straightforward - you don't have mass, so you add mass! But, alas, it's not. You can't just add stuff willy-nilly. I mean, you can of course. But see, the standard model is pretty much amazing. It is been heralded as the greatest scientific achievement. Ever. I mean, it was probably physicists making that claim, but still, pretty big. So if you just "add in mass" - which you can, you lose the beauty that is the standard model. So it has to be done carefully, it has to be done right. It has to be the Higgs.

The final note about the Higgs mechanism and the Higgs field that it describes, is that the field that allows for the mechanism to work "interacts with itself". Okay, that made no sense, but the effect is that you get the Higgs boson. Like how liquid water sort of condenses out of the air from gaseous form in some circumstances, a "condensate" of the Higgs field forms into a real particle just like the rest. It is through this particle that people hope to probe the nature of the Higgs field.

That's why we need the Higgs mechanism.