Measurement of the ground-state hyperfine structure of antihydrogen

The ASACUSA collaboration at CERN‐AD has recently submitted a proposal to measure the hyperfine splitting of the ground state of antihydrogen in an atomic beam apparatus [ASACUSA proposal addendum, CERN/SPSC 2005‐002, SPSC P‐307 Add.1 (2005)]. The apparatus consists of two sextupoles for spin selection and analysis, and a microwave cavity to flip the spin. This method has the advantage that antihydrogen atoms of temperatures up to 150 K ‘evaporating’ from a formation region can be used. Numerical simulations show that such an experiment is feasible if ∼100 antihydrogen atoms per second can be produced in the ground state, and that an accuracy of better than 10−6 can be reached. This measurement will be a precise test of the CPT invariance.