  We derive the scalar-tensor modification of the gravitational field of an
ultrarelativistic particle beam and its effect on a test particle that is used
as sensor. To do so, we solve the linearized scalar-tensor gravity field
equations sourced by an energy-momentum tensor of a moving point particle. The
geodesic equation and the geodesic deviation equation then predict the
acceleration of the test particle as well as the momentum transfer due to a
passing source. Comparing the momentum transfer predicted by general relativity
and scalar tensor gravity, we find that there exists a relevant parameter
regime where this difference increases significantly with the velocity of the
source particle. Since ultrarelativistic particles are available at
accelerators like the Large Hadron Collider, ultra-precise acceleration sensors
in the vicinity of the particle beam could potentially detect deviations from
general relativity or constrain modified gravity models.
