  We construct model wavefunctions for the half-filled Landau level
parameterized by "composite fermion occupation-number configurations" in a
two-dimensional momentum space which correspond to a Fermi sea with
particle-hole excitations. When these correspond to a weakly-excited Fermi sea,
they have large overlap with wavefunctions obtained by exact diagonalization of
lowest-Landau-level electrons interacting with a Coulomb interaction, allowing
exact states to be identified with quasiparticle configurations. We then
formulate a many-body version of the single-particle Berry phase for adiabatic
transport of a single quasiparticle around a path in momentum space, and
evaluate it using a sequence of exact eigenstates in which a single
quasiparticle moves incrementally. In this formulation the standard
free-particle construction in terms of the overlap between "periodic parts of
successive Bloch wavefunctions" is reinterpreted as the matrix element of a
"momentum boost" operator between the full Bloch states, which becomes the
matrix elements of a Girvin-MacDonald-Platzman density operator in the
many-body context. This allows computation of the Berry phase for transport of
a single composite fermion around the Fermi surface. In addition to a phase
contributed by the density operator, we find a phase of exactly $\pi$ for this
process.
