Development of a threshold aerogel Cherenkov detector for K∕π separation in the H-dibaryon search at J-PARC

We have developed a new threshold Cherenkov detector for online triggering in the H-dibaryon search experiment at the K1.8 beam line at J-PARC. Silica aerogel radiators with a refractive index of n=1.04 will cover an effective area of 550 × 220 mm2. The Cherenkov detector will be placed in a high magnetic field between two spectrometer magnets. Three prototypes and a real-size mockup module have been tested using pions and protons from photoproduction at SPring-8. For momentum ranging from 1.0 to 1.1 GeV ∕c, a suppression factor of 103 could be achieved for pions, with a factor of 10−2 for proton misidentification.