Abstract
Generalized parton distributions provide information on the distribution of quarks in impact parameter space. For transversely polarized nucleons, these impact parameter distributions are transversely distorted and this deviation from axial symmetry leads on average to a net transverse force from the spectators on the active quark in a DIS experiment. This force when acting along the whole trajectory of the active quark leads to transverse single-spin asymmetries. For a longitudinally polarized nucleon target, the transverse force implies a torque acting on the quark orbital angular momentum (OAM). The resulting change in OAM as the quark leaves the target equals the difference between the Jaffe–Manohar and Ji OAMs.
Highlights
Since the famous EMC experiments revealed that only a small fraction of the nucleon spin is due to quark spins [1], there has been a great interest in ‘solving the spin puzzle’, i.e. in decomposing the nucleon spin into contributions from quark/gluon spin and orbital degrees of freedom
The main advantages of this decomposition are that each term can be expressed as the expectation value of a manifestly gauge invariant local operator and that the quark total angular momentum
Recent lattice calculations of GPDs [3] yielded the surprising result that the light quark orbital angular momentum (OAM) is consistent with Lu ≈ −Ld, i.e. Lu + Ld ≈ 0
Summary
Since the famous EMC experiments revealed that only a small fraction of the nucleon spin is due to quark spins [1], there has been a great interest in ‘solving the spin puzzle’, i.e. in decomposing the nucleon spin into contributions from quark/gluon spin and orbital degrees of freedom In this effort, the Ji decomposition [2]. Lqz (and by subtracting the spin piece the the quark orbital angular momenta Lqz ) entering this decomposition can be accessed experimentally. The main advantages of this decomposition are that each term can be expressed as the expectation value of a manifestly gauge invariant local operator and that the quark total angular momentum. Recent lattice calculations of GPDs [3] yielded the surprising result that the light quark orbital angular momentum (OAM) is consistent with Lu ≈ −Ld, i.e. Lu + Ld ≈ 0. In which only one term is experimentally accessible, will not be discussed in this brief note
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