On the geometry of prequantization spaces

Given a Poisson (or more generally Dirac) manifold $P$, there are two approaches to its geometric quantization: one involves a circle bundle $Q$ over $P$ endowed with a Jacobi (or Jacobi-Dirac) structure; the other one involves a circle bundle with a (pre-) contact groupoid structure over the (pre-) symplectic groupoid of $P$. We study the relation between these two prequantization spaces. We show that the circle bundle over the (pre-) symplectic groupoid of $P$ is obtained from the groupoid of $Q$ via an $S^1$ reduction that preserves both the groupoid and the geometric structure.