Penning Trap Measurement of the Magnetic Moment of the Antiproton

The measurement of the magnetic moment (or g-factor) of the antiproton and of the proton is a sensitive test of CPT invariance. In our experiment we will store and detect a single (anti)proton in a cryogenic Penning trap. The g-factor will be measured by detection of quantum jumps via the continuous Stern-Gerlach effect. Most of the experimental techniques to be used have been already successfully employed by our group for the measurement of the g-factor of the bound electron in hydrogen-like ions. However, the magnetic moment of the proton is smaller than that of the electron by a factor of 658. Our hybrid trap design combines cylindrical electrodes with a toroidal ferromagnetic ring electrode. With this novel trap, spin-flip transitions of the (anti)proton can be detected by observation of tiny differences in the axial frequency by a phase-sensitive method. With our apparatus, we envisage to determine the g-factor of the (anti)proton with an accuracy of 10-9 or better