Abstract
Definitions of orbital angular momentum based on Wigner distributions are used as a framework to discuss the connection between the Ji definition of the quark orbital angular momentum and that of Jaffe and Manohar. We find that the difference between these two definitions can be interpreted as the change in the quark orbital angular momentum as it leaves the target in a DIS experiment. The mechanism responsible for that change is similar to the mechanism that causes transverse single-spin asymmetries in semi-inclusive deep-inelastic scattering.
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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