Investigating the Proton's Spin

So, what am I working on this summer? Why, some component projects in a much larger effort to explore what makes up the spin of the proton.

 Protons are an important part of the world around us. Most people are aware that the stuff we see in everyday life is made of much smaller constituents called molecules. Molecules are made out of atoms, and the study of how atoms interact to form molecules and how molecules interact is pretty much the fundamental goal of modern chemistry. Atoms are made out of smaller particles, a small dense region called the nucleus right at the center of an atom, and point-particles known as electrons. Electrons have a negative charge, and some of the particles in the nucleus have a positive charge equal to the charge on the electrons. These positive particles are known as protons. The other particles in the nucleus don't have a charge, and are known as neutrons.
But now that we know a little bit about what protons are, what do physicists mean by referring to it's spin. Way back in the nineteenth century and the early twentieth century, it seemed like physics had figured out how the world worked. There were a couple little mysteries, but it was assumed that they'd be figured out in next to no time (sound at all familiar?). To solve the problem of blackbody radiation, in 1900 Max Planck introduced the concept that the radiation was quantized. Blackbody radiation is the radiation given off by an object that absorbs all radiation hitting it. By saying that the emitted radiation was quantized, Planck meant that all of the radiation emitted from the object was in multiples of some fundamental amount of radiation.
Now, think about how weird that is. Rather than the energy being emitted being able to be any amount, it has to always be a multiple of some fundamental energy. It'd be like saying a car can't drive at any speed, but can only drive at multiples of half a mile per hour, or that a tree can't be of any height, but instead has to be in multiples of 3 inches tall. In the macroscopic world, the world we live in, this sort of thing makes no sense. But the fundamental energy Planck derived turns out to be a really, really small number. So this effect isn't all that noticeable. But, it revolutionized the way we do physics, especially at the scale of subatomic particles. It turns out a lot of things are quantized, and the study of how these systems behave is a little something called quantum mechanics.
One of the other things that nature says is quantized is angular momentum. Momentum is a quantity stuff has, and for a given object, it's proportional to the velocity of the object, and the object's mass. That's linear momentum. Angular momentum is when the object rotates, rather than travels in a straight line, and is proportional to the mass, radius of the rotation, and speed of the rotation. Like linear momentum, angular momentum is conserved. So, if a particle is rotating at a set radius at a set speed, it rotates faster if you bring it closer to the axis and slower if you drag it farther away. It turns out that this form of angular momentum is better termed orbital angular momentum, because it's what you get when things rotate around an axis. Very small things, like subatomic particles, also have an intrinisic angular momentum, which is what physicists are talking about when they talk about spin.
So, protons have some intrinsic angular momentum, known as spin, and it's been measured fairly well in modern experiments, and is known to be 1/2 h-bar. H-bar is the fundamental amount of angular momentum a particle can have, and is related to that quanitized energy Planck derived earlier.
Now, the thing is, protons are not fundamental particles. They're made up of smaller particles, called quarks. It used to be assumed that the sum of the spin of the quarks was what gave the proton it's spin. Experiments in the ninties have shown that this is not the case. So, there's a mystery as to where the proton spin is coming from. It's not the main three quarks, but there are other quarks there for physics reasons that I can explain later that might contribute. There are also gluons, which hold the quarks together, that might contribute. And finally, the parts making up the proton might orbit one another, contributing some orbital angular momentum to the intrinsic momentum of the proton. The collaboration I'm working with at the moment is trying to measure just one of these contributions, that of the gluons. And it's a lot of fun.