虽然不像大型同步加速器实验那样引人瞩目，但对基本常数或原子性质的测量也能为寻找“标准模型”以外的物理定律做出重要贡献——如果测量精度足够高的话。在一项直接测量中， Andreas Mooser 等人以前所未有的精度确定了质子的磁矩。这项测量是用一个double Penning trap进行的，它是一个在其中单个离子能够在一个强大的均匀磁场中被约束和操纵的系统。与对反质子磁矩的直接测量相结合，这项工作将会为对物质-反物质对称性的严格验证铺平道路。
One of the fundamental properties of the proton is its magnetic moment, µp. So far µp has been measured only indirectly, by analysing the spectrum of an atomic hydrogen maser in a magnetic field. Here we report the direct high-precision measurement of the magnetic moment of a single proton using the double Penning-trap technique. We drive proton-spin quantum jumps by a magnetic radio-frequency field in a Penning trap with a homogeneous magnetic field. The induced spin transitions are detected in a second trap with a strong superimposed magnetic inhomogeneity. This enables the measurement of the spin-flip probability as a function of the drive frequency. In each measurement the proton’s cyclotron frequency is used to determine the magnetic field of the trap. From the normalized resonance curve, we extract the particle’s magnetic moment in terms of the nuclear magneton: μp = 2.792847350(9)μN. This measurement outperforms previous Penning-trap measurements in terms of precision by a factor of about 760. It improves the precision of the forty-year-old indirect measurement, in which significant theoretical bound state corrections were required to obtain µp, by a factor of 3. By application of this method to the antiproton magnetic moment, the fractional precision of the recently reported value can be improved by a factor of at least 1,000. Combined with the present result, this will provide a stringent test of matter/antimatter symmetry with baryons.