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Defining the Observables for Quarks and Gluons Orbital Angular Momentum Distributions

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Abstract

We present a critical discussion of the observables that have been recently put forth to describe quarks and gluons orbital angular momentum distributions. Starting from a standard parameterization of the energy momentum tensor in QCD one can single out two forms of angular momentum, a so-called kinetic term, generally associated with the Ji decomposition, and a canonical term from the Jaffe Manohar decomposition. Orbital angular momentum has been connected to a Generalized Transverse Momentum Distribution (GTMD), for the canonical term, and to a twist three Generalized Parton Distribution for the kinetic term. We argue that while the latter appears as an azymuthal angular modulation in the longitudinal target spin asymmetry in deeply virtual Compton scattering, due to parity constraints, the GTMD associated with canonical angular momentum cannot be measured in a similar set of experiments.

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Authors and Affiliations

  1. Physics Department, University of Virginia, 382 McCormick Rd., Charlottesville, VA, 22904, USA

    S. Liuti & A. Rajan

  2. IFPA, AGO Department, Université de Liège, Bât. B5, Sart Tilman, 4000, Liège, Belgium

    A. Courtoy

  3. Department of Physics and Astronomy, Tufts University, Medford, MA, 02155, USA

    G. R. Goldstein

  4. Istituto Nazionale di Fisica Nucleare (INFN) - Sezione di Torino, via P. Giuria, 1, 10125, Turin, Italy

    J. O. Gonzalez Hernandez

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  1. S. Liuti
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  2. A. Courtoy
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  4. J. O. Gonzalez Hernandez
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  5. A. Rajan
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Correspondence to S. Liuti.

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Liuti, S., Courtoy, A., Goldstein, G.R. et al. Defining the Observables for Quarks and Gluons Orbital Angular Momentum Distributions. Few-Body Syst 56, 325–330 (2015). https://doi.org/10.1007/s00601-015-0950-7

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