Twisted particle collisions: A new tool for spin physics

Collisions of twisted particles---that is, non-plane-wave states of photons, electrons, or any other particle, equipped with a nonzero orbital angular momentum (OAM) with respect to its propagation direction---offer novel ways to probe particle structure and interactions. Recently, we argued that resonance production in twisted photon collisions or twisted ${e}^{+}{e}^{\ensuremath{-}}$ annihilation gives access to parity- and spin-sensitive observables in inclusive cross sections, even when the initial particles are unpolarized. Here, we explore these features in detail, providing a qualitative picture and illustrating it with numerical examples. We show how one can detect parity-violating effects in collisions of unpolarized twisted photons and how one can produce almost 100% polarized vector mesons in unpolarized twisted ${e}^{+}{e}^{\ensuremath{-}}$ annihilation. These examples highlight the unprecedented level of control over polarization offered by twisted particles, impossible in the usual plane wave collisions.