The barrel of the new CMS timing detector will consist of thousands of crystal sensors embellished around a cylindrical support structure that is the size of a small research submarine. When a passing particle hits a crystal, it generates a flash of light. This flash is immediately picked up by an attached photomultiplier, which converts the light into an electronic signal, which is then sent to a circuit board and time stamped. According to University of Virginia postdoc Bryan Cardwell, the con

University of Virginia postdoc Bryan Cardwell explains the simple math behind the new CMS timing detector that will let them calculate a key feature of particles: their mass. The two things they need are a measurement of how much the charged particles bend while they travel through CMS’s magnetic field (which gives momentum) and when the particles hit the timing detector (which gives velocity.) From this, they can use the equation momentum = mass x velocity to figure out the mass of the particle