Proton-electron mass ratio and the electron´s “Atomic Mass”

The UW Penning trap mass spectrometer has been used to improve the values for the electron´s atomic mass and the proton-electron mass ratio. The cyclotron frequency of small clouds of ⩽15 electrons is compared with the cyclotron frequency of a single trapped carbon ion (C ⁶⁺) in order to determine their relative mass ratio. In these comparisons, a relatively uniform magnetic field is used in order to assure that each particle sees (on the average) the same field. During systematic studies, the trapping potential was changed by more than a factor of two for the electron. In addition, measurements were taken versus axial and cyclotron drive power as well as the size of the electron cloud. Since the detection mechanism is through the nonharmonic content of the trapping potential, this too was varied. Upon correcting for the lost electrons in carbon, the comparison directly yields M_e =0.000 548 579 911 7(1 7) u. Using the accepted value for the proton´s atomic mass, we determine m_p/m_e=1836.152 6636(58). These values are limited primarily by the present stability of the magnetic field