Possibilistic clustering approach to trackless ring Pattern Recognition in RICH counters

The pattern recognition problem in Ring Imaging CHerenkov (RICH) counters concerns the identification of an unknown number of rings whose centers and radii are assumed to be unknown. In this paper we present an algorithm based on the possibilistic approach to clustering that automatically finds both the number of rings and their position without any a priori knowledge. The algorithm has been tested on realistic Monte Carlo LHCb simulated events and it has been shown very powerful in detecting complex images full of rings. The tracking-independent algorithm could be usefully employed after a track based approach to identify remaining trackless rings.