Remeasurement of the magnetic moment of the antiproton

A high-precision measurement of the finestructure splitting in the circular 11→10 X-ray transition of\(\bar p^{208} Pb\) was performed. The experimental value of 1199(5) eV is in agreement with QED calculations. From that value the magnetic moment of the antiproton was deduced to be −2.8005(90)μnucl. With this result the uncertainty of the previous world average value was reduced by a factor of ≈2. A comparison with the corresponding quantity of the proton now yields:\({{\left( {\mu _p - \left| {\left\langle {\mu _{\bar p} } \right\rangle } \right|} \right)} \mathord{\left/ {\vphantom {{\left( {\mu _p - \left| {\left\langle {\mu _{\bar p} } \right\rangle } \right|} \right)} {\mu _p }}} \right. \kern-\nulldelimiterspace} {\mu _p }} = \left( { - 2.4 \pm 2.9} \right) \times 10^{ - 3} \).