Interaction point
In particle physics, an interaction point is the place where particles collide in an accelerator experiment. The nominal interaction point is the design position, which may differ from the real or physics interaction point, where the particles actually collide. A related, but distinct, concept is the primary vertex: the reconstructed location of an individual particle collision.
For fixed target experiments, the interaction point is the point where beam and target interact. For colliders, it is the place where the beams interact.
Experiments at particle accelerators are built around the nominal interaction points of the accelerators. The whole region around the interaction point is called an interaction region.
Particle colliders such as LEP, HERA, RHIC, Tevatron and LHC can host several interaction regions and therefore several experiments taking advantage of the same beam.
