Question: what are pixel detectors

Clara Nellist answered on 13 Mar 2014:

A question close to my heart!

The detectors I work with are very similar to the sensor inside your digital camera but instead of taking selfies, they are used to take pictures of particles. The sensor is split into lots of little tiles, like a kitchen floor and this tells us how clear our image will be. The more pixels we have, and the smaller they are, the clearer the image.

In a camera and in the detector, the sensor is the part that actually records the data (either light, or in my case, any particle with electrical charge). When a new particle like a Higgs boson is made, it doesn’t stick around very long and quickly changes into lots of lighter particles. Our detector essentially takes a picture of these other particles that have been created to be able to go back later and work out what they were. Then we can say that a Higgs was there.

Also, when you buy a new camera, it tells you how many pixels you have, like 10 megapixels, or 16 megapixels and this gives you an idea of how much detail you’re going to be able to save in your photo. You can try comparing a zoomed in photo from your phone with one from a digital camera. The one from the phone will start to show the pixels a lot sooner. Part of my work is to make the pixels in our sensors smaller so we can get more of them in one place and take a clearer image, just like upgrading your camera from 10->16 megapixels.

Unlike a camera though, the detectors I work with get damaged by the particles that pass through them and over time they don’t work as well as they used to. So my job is to try to design better sensors that can take all the punishment of working in a very radioactive environment. Especially since the Large Hadron Collider at CERN is going to be working at higher energies from next year. Which means more radiation and more damage!