19 May 2009

The International Linear Collider

For my friends and family who wonder what the heck I'm doing, hopefully this post will clarify my research project and its place in the larger goals of particle physics.

First, I should probably say that no, I'm not working on the LHC. While the LHC is totally sweet and not going to destroy the world, I'm working on the next particle accelerator, the one that will come after the LHC. It's called the International Linear Collider, and it hasn't even been built yet, but it's pretty exciting to see such a huge project in its infancy.

Why do we need the ILC? Isn't the LHC enough? Well, it turns out that in order to reach the energies needed to test for stuff like the existence of extra dimensions, dark matter, and the Higgs boson, the LHC is actually the quick, dirty, and cheap solution. The folks at CERN basically just upgraded the cavern holding the old Large Electron-Positron collider to make space for the new LHC equipment. Okay, so maybe "just" is an understatement, but all the basic infrastructure to support a new accelerator was already in place.

The LHC's limitation, however, is that CERN is circular: Because of this, the LHC is really only good for smashing protons (when you spin particles in a circle, they lose energy in an inverse proportion to their mass, so it would be very inefficient for electrons and positrons). Unfortunately, protons are really messy. Instead of being a point particle like an electron, a proton is actually made up of three quarks stuck together by the strong force.

Shooting electrons at each other is like playing pool - it's easy to follow the chain of collisions. Shooting protons together, however, is more like throwing two bags of billiard balls at each other - it's a messy process and it's hard to tease out what happens afterwards. So while the LHC is a good way to get a first look at terascale energies, if you want any kind of precision you need a linear electron-positron collider - and that's what the ILC is for:

(sorry for the small size; click 'er for bigger)

Obviously, there are still some questions. For example, the LHC energy goes up to ~15 TeV; why can the ILC get away with only 500 GeV? I don't actually know the answer. I suspect it has to do with the efficiency of energy transfer during collisions (as per the previous paragraph), but I'm not sure. Hey, I just work here, you know?
(Actually, part of my motivation to write this blog is to force myself to find these kinds of answers. It's not like you go study physics for a couple years and suddenly everything becomes clear.)

For the next three years (almost 2.5, yeesh!), I'll get to grind through every agonizing detail that goes into making an experiment like this work. My responsibility (and that of my research group) is to design one of the particle detectors, called LumiCal for "luminosity calorimeter." I'll post some other time about how what this is and how it fits into the ILC as a whole and how being a code monkey is actually a great thing to do right now (it is, I swear!); right now, this is a decent summary of the big picture surrounding my research job.

Addendum: Symmetry Magazine has a pretty good article describing the design of the ILC


Anonymous said...

Code monkeys was a great show

aeb said...

ssssso far they meet in intereesting places: Snowmass, Colorado and Frascati (?sp) Italy. Hope you get to go!

Jack said...

Nice to see you are up to something useful. How is the research going? I am at CERN at the moment with Joao working on ATLAS commissioning...or right now leaning data analysis software. It's all the same, I guess. How have you been?

Jack K
We TFed together? Remember? Sure you do...