Purpose

• a positive kaon identification
• a destinction of gammas and relativistic charged particles entering the EMC behind him

Working principle

• Cherenkov Detector
• determination of the mass of the particle by combining his velocity information with momentum information from the tracking detectors

Important values

• Polar angle vs. momentum distribution of the kaons in radiative decays of resonances in formation experiments like J/psi -> K+K- gamma for the search of glue-balls (Ref. TPR):
  

• the barrel DIRC covers the solid angle of 22 to 140 degrees
• the lower momentum threshold for kaons which produce Cherenkov light is for an envisaged refractive index of n=1.47 as low as 460 MeV/c (for single photon producton -- for photon numbers bigger than 4 it is more than 200 MeV/c higher)

FIRST Estimations:

• Single Photon Cherenkov Angle Resulution

• • with a DIRC-Bar size of 17x30x2000mm, a distance of l=1.20m of the photomultipiers from the bar exit and a diameter of the photomultiplier cathods of 2cm ( beeing equal to the distance of the centers of the cathods) the geometric contribution of the Single Photon Cherenkov Angle Resulution can be calculated

• • to this geometric contribution the resolution contribution (comming from the production and the transmission dispersion) has to be added which has a values of similar size