Mar 19 – 23, 2018
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Transverse dynamics of quarks in the proton - from Ji to Jaffe-Manohar orbital angular momentum

Mar 22, 2018, 9:50 AM


Michael Engelhardt


Quark orbital angular momentum (OAM) in the nucleon can be evaluated
directly by employing a Wigner function embodying the simultaneous
distribution of parton transverse position and momentum. This
distribution can be accessed via a generalization of the nucleon
matrix elements of quark bilocal operators which have been used
previously in the lattice evaluation of transverse momentum
dependent parton distributions (TMDs). By supplementing these matrix
elements with a nonzero momentum transfer, mixed transverse position
and momentum information is generated. In the quark bilocal operators,
a gauge connection between the quarks must be specified; a staple-shaped
gauge link path, as used in TMD calculations, yields Jaffe-Manohar OAM,
whereas a straight path yields Ji OAM. A lattice calculation at a pion
mass of 518 MeV is presented which demonstrates that the difference
between Ji and Jaffe-Manohar OAM can be clearly resolved. The obtained
Ji OAM is confronted with traditional evaluations utilizing Ji's sum
rule. Jaffe-Manohar OAM is enhanced in magnitude compared to Ji OAM.

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