  We establish a link between two geometric approaches to the representation
theory of rational Cherednik algebras of type A: one based on a noncommutative
Proj construction, used in [GS]; the other involving quantum hamiltonian
reduction of an algebra of differential operators, used in [GG].
  In the present paper, we combine these two points of view by showing that the
process of hamiltonian reduction intertwines a naturally defined geometric
twist functor on D-modules with the shift functor for the Cherednik algebra.
That enables us to give a direct and relatively short proof of the key result,
[GS, Theorem 1.4] without recourse to Haiman's deep results on the n! theorem.
We also show that the characteristic cycles defined independently in these two
approaches are equal, thereby confirming a conjecture from [GG].
