The role of post-selection in generating vortex particles of arbitrary mass, spin, and energy

Promises and challenges of high-energy vortex states collisions

“…The price to pay is the necessity of a post-selection protocol, a rather exotic requirement for particle physics. Although this idea was already used in the first publications on high-energy processes with vortex particles [32,33,274,153], its general description was presented only very recently [47,48]. Below, we follow the main arguments from these recent publications.…”

“…These arguments were recently developed in [47,48] in a more formal way in terms of the strong postsection protocol which is always implicitly applied when we discuss measurements with traditional local detectors, see more discussion in Section 5.2.2.…”

“…With the choice of spinors w (λ) which depend on the azimuthal angle as exp(±iϕ k /2), the bispinor is defined up to an overall sign and also does not have a well-defined forward limit, see discussion on this issue in [48]. For an alternative, equally possible convention, see [34].…”

“…At present, no such detectors exist, at least for high-energy particles. As we discussed in Section 2.2, a standard detector instrumentation will be of little use: as long as one detects an outgoing particle in a certain direction, one loses information about its ϕ-dependent phase [47,48]. These challenge may be less severe for processes featuring very narrow angular distributions of one of the final particles, such as Compton backscattering from ultrarelativistic electrons [32,33].…”

“…In [47,48], this final state was called pre-selected, or evolved state, to clearly distinguish it from what a detector will eventually record. This outgoing state may include several reaction channels which are kinematically possible as well as a non-scattered contribution of the initial particles [146].…”