Detection of cold antihydrogen annihilation

The ATRAP experiment at the CERN antiproton decelerator AD aims for a test of the CPT invariance by a high precision comparison of the 1s-2s transition between the hydrogen and the antihydrogen atom [1]. The experimental studies are performed at two separate installations, ATRAP-I, a system with severe space limitation, where routinely antihydrogen was produced [2],[3] and ATRAP-II, which will start full operation within the next AD running period. ATRAP-II includes a much larger solenoid allowing the installation of an extended detection system as well as an optimized loffe trap. The antihydrogen annihilation detector system consists of several layers of scintillating fibers, counts the antihydrogen atoms and determines the annihilation vertex of the atoms. This diagnostic element will allow to optimize the production of cold antihydrogen sufficiently to permit the optical observations and measurements. Measurements are in progress to check the performance and specifications of the antihydrogen annihilation detector. Extensive Monte Carlo simulations concerning the track reconstruction have been started and will be continued using the program GEANT4.