Understanding Bell locality tests at colliders

For decades, it has been known that generic local hidden-variable theories cannot be disproved by collider experiments involving decaying particles. However, if these theories satisfy a small set of mild assumptions, they become testable. In particular, this class of theories can be disproved using Bell-like inequalities for μ ⁺ μ ⁻ μ + μ - and τ ⁺ τ ⁻ τ + τ - pairs.