Hyperfine spectroscopy of hydrogen and antihydrogen in ASACUSA.

The ASACUSA collaboration at the Antiproton Deceleratorof CERN aims at a precise measurement of the antihydrogenground-state hyperfine structureas a test of the fundamental CPT symmetry. A beam of antihydrogenatoms is formed in a CUSP trap, undergoes Rabi-type spectroscopyand is detected downstream in a dedicated antihydrogendetector. In parallel measurements using a polarized hydrogen beam are being performed to commission the spectroscopyapparatus and to perform measurements of parameters of the Standard Model Extension(SME). The current status of antihydrogen spectroscopyis reviewed and progress of ASACUSA is presented.