New high-precision comparison of electron and positron g factors

Single electrons and positrons have been alternately isolated in the same compensated Penning trap in order to form the geonium pseudoatom under nearly identical conditions. For each, the g-factor anomaly is obtained by measurement of both the spin-cyclotron difference frequency and the cyclotron frequency. A search for systematic effects uncovered a small (but common) residual shift due to the cyclotron excitation field. Extrapolation to zero power yields $e^{+}$ and $e^{\mathrm{-}}$ g factors with a smaller statistical error and a new particle-antiparticle comparison: g($e^{\mathrm{-}}$)/ g($e^{+}$)=1+(0.5±2.1)×${10}^{-12}$. . AE