A RICH detector for hadron identification at JLab

The “standard” Hall A apparatus at Jefferson Lab (TOF and aerogel threshold Cherenkov detectors) does not provide complete identification for proton, kaon and pion. To this aim, a proximity focusing C 6F 14/CsI RICH (Ring Image CHerenkov) detector has been designed, built, tested and operated to separate kaons from pions with a pion contamination of a few percent up to 2.4 GeV/ c. Two quite different experimental investigations have benefitted of the RICH identification: on one side, the high-resolution hypernuclear spectroscopy series of experiments on carbon, beryllium and oxygen, devoted to the study of the lambda-nucleon potential. On the other side, the measurements of the single spin asymmetries of pion and kaon on a transversely polarized 3He target are of utmost interest in understanding QCD dynamics in the nucleon. We present the technical features of such a RICH detector and comment on the presently achieved performance in hadron identification.