  It is known that the center-of-mass energy of the collision of two massive
particles following geodesics around a black hole presents a maximum. The
maximum energy increases when the black hole is endowed with spin, and for a
maximally rotating hole this energy blows up, offering, in principle, a unique
probe of fundamental physics. This work extends the latter studies by
considering that the colliding particles possess intrinsic angular momentum
(spin), described by the Hanson-Regge-Hojman theory of spinning particles. By
analyzing planar trajectories of spinning particles around non-rotating black
holes, a significant increase of the invariant collision energy is found.
Radial turning points, causality constraints, and limitations of the theory are
discussed.
