  We have performed a systematic high-momentum-resolution photoemission study
on ZrTe$_5$ using $6$ eV photon energy. We have measured the band structure
near the $\Gamma$ point, and quantified the gap between the conduction and
valence band as $18 \leq \Delta \leq 29$ meV. We have also observed
photon-energy-dependent behavior attributed to final-state effects and the 3D
nature of the material's band structure. Our interpretation indicates the gap
is intrinsic and reconciles discrepancies on the existence of a topological
surface state reported by different studies. The existence of a gap suggests
that ZrTe$_5$ is not a 3D strong topological insulator nor a 3D Dirac
semimetal. Therefore, our experiment is consistent with ZrTe$_5$ being a 3D
weak topological insulator.
