Guidance on using this applet

General notes

This applet simulates the LHCb Ring Imaging Cherenkov detectors. A RICH detector comprises a radiator volume and an optical system for focussing and detecting Cherenkov photons.

Cherenkov radiation is emitted when charged particles like protons, kaons or pions pass through the radiator volume. The radiator can be any material having a refractive index greater than 1.0. LHCb uses both solid (Aerogel, index=1.03) and gaseous (C4F10, index=1.0014) radiators.

In LHCb the optical system uses spherical mirrors to focus the cherenkov photons onto the image plane. The LHCb RICH detectors are split in two halves and the half mirrors are tilted at +/-18deg. with respect to the LHC beam axis in order that the ring image plane is moved away from the beam.

This applet allows charged particles to be interactively generated and simulates the subsequent propagation and Cherenkov radiation.

Particle controls

These controls allow you to change the particle identification properties of the incident particles.

You can choose amongst a preset list of particle types (pion, kaon, proton...) whose masses are known, or you can select "Other" and invent a particle with a mass of your choice.

You may also choose to select a particle type at random.

Miscellaneous controls

• Frame speed. This parameter sets the number of frames per second and can be used to control the apparent speed of the animation. High numbers implies slower apparent speed (and uses more CPU time).
• Projection. Ray tracing and particle propagation is always done in full 3 dimensions. However, the side elevation can be drawn either by plane projection of the Cherenkov photons or by a conical projection. The convergence of the Cherenkov photons on the focal plane and the conical Cherenkov wavefront is more apparent in the conical projection.
• Radiator refractive index. The Cherenkov photons are emitted in a cone about the incident particle direction. The half angle of the cone is given by acos(1/Bn), where B is the particle speed as a fraction of the speed of light in vacuo and n is the radiator refractive index. B is calculated from the particle momentum.

Momentum controls

The generated primary particle momentum can be set at random for each particle or fixed to the values specified by the "Momentum" and "Angle" fields. Momentum is a vector quantity hence both the maginitude and direction are required for it to be fully specified.

Shooting range

Particles may be generated one-at-a-time on demand ("Fire now") or automatically at random time intervals. If random shooting is selected the average rate may be set.

Particles may also be generated using the mouse. Click and hold at the point where you want the particle to start then drag back towards the origin. Now release to generate the particle. The momentum is set proportional to the distance dragged and the direction is given by the line joining the release and press points. Imagine a sort of catapult action.