Abstract
Collisions of twisted particles --- that is, non-plane-wave states of photons, electrons, or any other particle, equipped with a non-zero orbital angular momentum (OAM) with respect to its propagation direction --- offer novel ways to probe particle structure and interactions. In the recent paper \cite{Ivanov:2019vxe}, we argued that resonance production in twisted photon collisions or twisted $e^+e^-$ 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 $e^+e^-$ annihilation. These examples highlight the unprecedented level of control over polarization offered by twisted particles, impossible in the usual plane wave collisions.
Highlights
Determining the spin and parity properties of hadrons is an intricate and fascinating aspect of modern particle phenomenology
We showed that if one prepares initial particles in the so-called twisted state, in which they are equipped with a nonzero, adjustable orbital angular momentum (OAM) with respect to their propagation direction, spin- and parity-dependent observables can be probed with fully inclusive cross sections of unpolarized particles
We demonstrated that unpolarized twisted photon collision has a new intrinsic, adjustable degree of freedom, which is absent in the plane wave case: a difference between σλ1⁄4þ1 and σλ1⁄4−1
Summary
Determining the spin and parity properties of hadrons is an intricate and fascinating aspect of modern particle phenomenology. Deep inelastic scattering (DIS) with a polarized initial lepton or proton allows one to investigate how spin of the ultrarelativistic proton emerges from spins and orbital angular momenta of its constituents [6]. One can study exclusive or semi-inclusive reactions; look into angular distribution of the final state particles; and, with the aid of partial-wave analysis, deduce the spin properties either of the target hadron (in DIS) or of the intermediate resonances (in low-energy exclusive production processes). We showed that if one prepares initial particles in the so-called twisted state, in which they are equipped with a nonzero, adjustable orbital angular momentum (OAM) with respect to their propagation direction, spin- and parity-dependent observables can be probed with fully inclusive cross sections of unpolarized particles.
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