Question: When colliding particles, how do you measure and detect the subsequent particles that may appear as a result of the collision?

Jonathan Edward Davies answered on 8 Mar 2023:

There are lots of different technologies that we use to work out what happened. For instance, when a charged particle (for example an electron) passes through a silicon chip it leaves a little electrical signal that we can pick up. If we have lots of layers of these chips then we can do something like a dot-to-dot to work out the path that the particle took.

You can do a similar sort of thing by measuring the ionisation of a chamber of gas by a charged particle.

We also use very big magnets- charged particles will bend in a magnetic field depending on the sign of their charge and their momentum (how fast they’re moving).

There’s also a cool effect that we can make use of- if a particle travels through a material faster than the speed of light in that material (you can’t go faster than the speed of light in a vacuum but for instance this speed is a bit lower in water) then it will give off particles of light (photons) in a cone shape around its path. This type of radiation is why in movies you see nuclear reactors with glowing tanks of water. The angle of the cone shape also gives us more information on the type of particle based on its speed.

We also have “calorimeters” where we destroy the particles to make them lose all their energy. We can measure this loss of energy and this gives us even more information that we can use.

We make use of some sophisticated software that will automatically combine together all this information so for a certain proton-proton collision we have an idea of the types of particles that were produced, as well as their energies, momenta and other properties.