A critical appraisal of tests of locality and of entanglement versus non-entanglement at colliders

TL;DR

This paper critically examines the feasibility of testing quantum locality and entanglement at particle colliders, reaffirming that current experimental limitations prevent such tests and clarifying the scope of existing no-go theorems.

Contribution

It provides a detailed analysis showing that collider experiments cannot coherently test locality or entanglement, reaffirming the validity of the no-go theorem in this context.

Findings

Current collider experiments cannot perform coherent tests of locality.

Indirect measurements via angular correlations do not suffice to test entanglement.

The no-go theorem remains valid for collider-based tests of locality.

Abstract

It has been argued more than 30 years ago that it is not possible to test locality at colliders, due to the inability to directly measure non-commutating observables such as spin components in current collider experiments. Recently, there has been a lot of phenomenological and experimental activity around testing locality via Bell-type experiments or entanglement versus non-entanglement in a collider environment. These results seem to evade the earlier no-go theorem by indirectly measuring spin correlations via their relation to angular correlations between momenta. We perform a careful study of the feasibility of such an approach. We scrutinize the relationship between spin and angular correlations in both quantum mechanics and local hidden variable theories. Our conclusion is that it is currently not possible to perform a logically coherent set of experimental measurements at colliders that would allow one to test locality or entanglement versus non-entanglement. This reaffirms the earlier no-go theorem. We stress that the no-go theorem does not apply to measurements of observables inspired from entanglement and Quantum Information Theory to test the Standard Model of particle physics.