Item

Abstract

Invariance under the charge, parity, time-reversal (CPT) transformation is one of the fundamental symmetries of the standard model of particle physics. This CPT invariance implies that the fundamental properties of antiparticles and their matter-conjugates are identical, apart from signs. There is a deep link between CPT invariance and Lorentz symmetry—that is, the laws of nature seem to be invariant under the symmetry transformation of spacetime— although it is model dependent. A number of high-precision CPT and Lorentz invariance tests—using a co-magnetometer, a torsion pendulum and a maser, among others—have been performed, but only a few direct high-precision CPT tests that compare the fundamental properties of matter and antimatter are available. Here we report high-precision cyclotron frequency comparisons of a single antiproton and a negatively charged hydrogen ion (H^-) carried out in a Penning trap system. From13,000 frequencymeasurements we compare the charge-to-mass ratio for the antiproton (q/m)_p- to that for the proton (q/m)_p and obtain (q/m)_p-/(q/m)_p--1=1(69) x 10^-12. The measurements were performed at cyclotron frequencies of 29.6 megahertz, so our result shows that the CPT theorem holds at the atto-electronvolt scale. Our precision of 69 parts per trillion exceeds the energy resolution of previous antiproton-toproton mass comparisons7,9 as well as the respective figure of merit of the standardmodel extension10 by a factor of four. In addition,we give a limit on sidereal variations in the measured ratio of <720 parts per trillion.By following the arguments of ref. 11, our result can be interpreted as a stringent test of the weak equivalence principle of general relativity using baryonic antimatter, and it sets a new limit on the gravitational anomaly parameter of |a_g-1|<8.7 x 10^-7.