The equivalence of chirality and helicity for strictly massless particles is a foundational kinematic result in relativistic quantum mechanics and standard model physics, requiring no specialized paper citation.
The claim is a standard textbook property of massless fields in particle physics (helicity and chirality coincide because the little group for massless particles is ISO(2) or U(1), and chirality operators project onto helicity eigenstates in the zero-mass limit). None of the retrieved papers specifically target or test this standard definition as a novel empirical finding; rather, it is foundational background knowledge. Therefore, it is categorized as common knowledge for physics contexts.