  When a charged particle penetrates through an optical interface, photon
emissions emerge - a phenomenon known as transition radiation. Being paramount
to fundamental physics, transition radiation has enabled many applications from
high-energy particle identification to novel light sources. A rule of thumb in
transition radiation is that the radiation intensity generally decreases with
the particle velocity v; as a result, low-energy particles are not favored in
practice. Here we find that there exist situations where transition radiation
from particles with extremely low velocities (e.g. v/c<0.001) exhibits
comparable intensity as that from high-energy particles (e.g. v/c=0.999), where
c is light speed in free space. The comparable radiation intensity implies an
extremely high photon extraction efficiency from low-energy particles, up to
eight orders of magnitude larger than that from high-energy particles. This
exotic phenomenon of low-velocity-favored transition radiation originates from
the excitation of Ferrell-Berreman modes in epsilon-near-zero materials. Our
findings may provide a promising route towards the design of integrated light
sources based on low-energy electrons and specialized detectors for
beyond-standard-model particles.
