Determination of the electron's atomic mass and the proton/electron mass ratio via Penning trap mass spectroscopy

Accuracy of the electron's atomic mass has been improved tenfold by comparing cyclotron frequencies of electrons and single C⁶⁺ ions alternately confined to the same uniform magnetic field in a Penning trap. Cyclotron resonances are observed via frequency shifts in the particle's continuously monitored harmonic motion parallel to the field. Field instability and relativity cause, respectively, the leading statistical and systematic errors. Combining the electron's atomic mass M_e=0.000 548 579 911 1(12)u with the proton's yields the mass ratio m_p/m_e=1836.152 666 5(40).