Ring recognition in the HADES second-level trigger

Abstract The online ring recognition processor of the HADES second level trigger is described. It performs a search for Cherenkov rings of fixed diameter using the hit pattern information from the RICH detector. A complete pad plane is processed in less than 10 μ s with a ring finding efficiency greater than 90%. In combination with the information from the other detector subsystems, an event reduction factor of about 100 is obtained by the second level trigger.