Gluon polarization in the nucleon demystified

Recently, X. Chen et al. proposed a new approach to the gauge invariant decomposition of the nucleon spin into the helicity and orbital angular momentum of quarks and gluons. The key ingredient in their construction is the separation of the gauge field into physical and “pure gauge” parts. We suggest a simple separation scheme and show that the resulting gluon helicity coincides with the first moment of the conventional polarized gluon distribution measurable in high energy experiments