  We consider entanglement entropy of a cap-like region for a conformal field
theory living on a sphere times a circle in d space-time dimensions. Assuming
that the finite size of the system introduces a unique ground state with a
nonzero mass gap, we calculate the leading correction to the entanglement
entropy in a low temperature expansion. The correction has a universal form for
any conformal field theory that depends only on the size of the mass gap, its
degeneracy, and the angular size of the cap. We confirm our result by
calculating the entanglement entropy of a conformally coupled scalar
numerically. We argue that an apparent discrepancy for the scalar can be
explained away through a careful treatment of boundary terms. In an appendix,
to confirm the accuracy of the numerics, we study the mutual information of two
cap-like regions at zero temperature.
