If we've created particles in a collision in an accelerator, we want to be able to look at them. And that's where particle detectors come in. We build these at the collision points in an accelerator and use them to identify as much of what was produced in the collision as we can.
The principle of a particle detector is simple. It will never “see” a particle directly, but shows where it has travelled, what signature tracks it leaves behind and the effect it has on the detector when it is stopped as it flies out of the collision.
Detectors consist of layers of different types of material which are used to either show us the path of a particle as it travels along, or absorb it to make the particle stop.
We can identify different types of particles depending on where they stop in the detector, and what their path of travel looks like. It is a bit like a police investigation after a car crash - if we know what particles were produced in the collision, in which direction they flew and how much energy they had, we can reconstruct what exactly happened in the collision.
In particle physics, reconstructing the particle collision means you can find new types of particles and work out how they interact with each other.
Big! Current experiments are as big as a house. ATLAS, an experiment that will run at the LHC, will be as big as a cathedral. Detectors have to be this big to stop highly energetic particles that were travelling near the speed of light.
From the outside, detectors look like huge boxes, with literally kilometers of cables attached. These cables carry electronic signals from inside the detector to computers outside to be processed. If you could see inside you'd see onion-like layers of materials like silicon, plastic, steel, lead glass and lots of support structure to hold the whole thing together.
The data pouring out of these detectors will be analysed to answer fundamental questions about the way the universe works......