A graph showing the angle at a given momentum for different particle species
The emission angle of Cherenkov radiation measured as a function of each particle's momentum showing bands for different particle species.

Imperial's main focus on the detector is the experiments ring imaging Cherenkov (RICH) detectors. These are used to identify different species of long-lived charged hadrons (pions, kaons, protons, and deuterons). Cherenkov radiation (the familiar glow around radioactive materials in films) is emitted when a particle travels faster than the speed light will travel in a particular medium. The photons are emitted at an angle with respect to the particle that depends on the particle's speed, producing a cone of light. Spherical mirrors are used to focus this cone into rings on our photon detectors, where the radius of the ring tells us the speed of the particle. Combining this information with the momentum of the particle measured from the tracking system, the particle's mass, and hence type, can be computed. An example of the measured angle at a given momentum for different particle species is shown to the left.

A picture of the constructed photon detector
Imperial designed and build mechanics for the Upgraded RICH detector before installation at CERN.

These detectors are currently undergoing a major upgrade, and imperial has a major role in development, construction, commissioning, and operation of these detectors. We have designed and build the mechanics for holding the photon detectors in place which can be seen in the image right, and developed a modular system to allow fast maintenance. We will play a leading role in commissioning the full detector chain both in the lab and in situ at the experiment.