  An equality of particle and antiparticle gravitational interactions holds in
general relativity and is supported by indirect observations. Gravity
dependence on rotation or spin direction is experimentally constrained for
non-relativistic matter. Here a method based on high energy Compton scattering
is developed to measure the gravitational interaction of accelerated charged
particles. Within that formalism the Compton spectra measured at HERA rule out
the speculated anti-gravity possibility for antimatter at a confidence level
close to 100%. The same data, however, imply a gravitational CP violation
around 13 GeV energies, by a maximal amount of 9 +/- 2 ppt for the charge and
13 +/- 3 ppt for the space parity. The detected asymmetry hints for a stronger
gravitational coupling to left helicity electrons relative to right helicity
positrons.
