Doing spin physics with unpolarized particles

TL;DR

This paper explores how twisted particles with orbital angular momentum can be used in particle collisions to reveal new spin and parity information, enabling novel measurements with unpolarized initial states.

Contribution

It introduces a theoretical framework for using twisted particles in resonance production and $e^+e^-$ annihilation to probe spin and parity-sensitive observables.

Findings

Twisted states break left-right symmetry even with unpolarized particles.

Almost 100% polarized vector mesons can be produced in unpolarized twisted $e^+e^-$ annihilation.

Control over the polarization state of produced particles is achievable.

Abstract

Twisted, or vortex, particles refer to freely propagating non-plane-wave states with helicoidal wave fronts. In this state, the particle possesses a non-zero orbital angular momentum with respect to its average propagation direction. Twisted photons and electrons have been experimentally demonstrated, and creation of other particles in twisted states can be anticipated. If brought in collisions, twisted states offer a new degree of freedom to particle physics, and it is timely to analyze what new insights may follow. Here, we theoretically investigate resonance production in twisted photon collisions and twisted $e^+e^-$ annihilation and show that these processes emerge as a completely novel probe of spin and parity-sensitive observables in fully inclusive cross sections with unpolarized initial particles. This is possible because the initial state with a non-zero angular momentum explicitly breaks the left-right symmetry even when averaging over helicities. In particular, we show how one can produce almost $100\%$ polarized vector mesons in unpolarized twisted $e^+e^-$ annihilation and how to control its polarization state.