A χ2 test used for particle identification with the Hall A RICH detector at JLab

An algorithm, based on the χ2 test, employed for particle identification by RICH detectors, is described. This algorithm is independent and complementary to the traditional algorithm based on the comparison between the average of the measured Cherenkov angles and the expected Cherenkov angles of the photons generated in the RICH by the particle to be identified. On the other hand it is much simpler and faster than a full likelihood analysis of the full event pattern. The particle rejection ratios achievable with the combined use of this algorithm and the algorithm based on the comparison between the average and the expected Cherenkov angles are very high. The algorithm also allows one to identify noise easily. The application of the algorithm is shown for the Hall A RICH detector in the E94-107 experiment at JLab. In this experiment an enormous background made up of pions and protons is 30 000 times bigger than the signal and had to be identified and rejected in order to extract the kaons from the electroproduction of hypernuclei.