BASE is a multinational collaboration at the Antiproton Decelerator (AD) of CERN which aims at precise comparisons of the fundamental properties of antiprotons and protons. Such comparisons are interesting because any measured asymmetry would hint at physics beyond the Standard Model. The experiment consists of measuring the cyclotron and Larmor frequencies of single trapped (anti)protons, and optionally negatively charged hydrogen ions. By measuring the ratio of these two frequencies the magnetic moment of the (anti)proton is obtained in units of the nuclear magneton. The BASE collaboration observed the first spin flips with a single trapped proton, measured the magnetic moment of the proton with a fractional precision at the ppm level, observed first single proton spin filps and demonstrated the double Penning trap technique for the first time. Recently we performed the first direct high-precision measurement of the magnetic moment of a single trapped proton. Our value has a precision of 3.3 ppb, outperforms previous Penning trap experiments by a factor of 760, and improves the currently acceped CODATA literature value by a factor of 2.5. By applying this technique to the antiproton magnetic moment a 1000-fold improvement in precision is possible, which will provide one of the most sensitive tests of CPT invariance.
In addition we performed the most precise test of CPT invariance with baryons by comparing the antiproton-to-proton charge-to-mass ratio with a fractional precision of 69 parts in a trillion. We aim at improving this measurement by another factor of 10.