One of the things they're looking for is a unit of graviton. This particle is thought, in string theory, to possibly transcend different dimensions.
It's interesting to think that we're spending billions of dollars on a big machine that's testing for alternate dimensions and universes. Many of the theories of modern physics are just impossible to grasp.
Blows your mind.
One of my favorite programs of all time. Brian Greene is a little cheesy (but smart as shit), but it's an interesting take on modern physics.