Speaker
Description
Generalized transverse momentum-dependent parton distributions (GTMDs)
provide a comprehensive framework for imaging the internal structure of
the proton. In particular, by encoding the simultaneous distribution of
quark transverse positions and momenta, they allow one to directly access
longitudinal quark orbital angular momentum, and, moreover, to
correlate it with the quark helicity. The relevant GTMD is evaluated
through a lattice calculation of a proton matrix element of a quark
bilocal operator (the separation in which is Fourier conjugate to the
quark momentum) featuring a momentum transfer (which is Fourier conjugate
to the quark position), as well as the Dirac structure appropriate for
capturing the quark helicity. The weighting by quark transverse position
requires a derivative with respect to momentum transfer, which is obtained
in unbiased fashion using a direct derivative method. The lattice
calculation is performed directly at the physical pion mass, using
domain wall fermions to mitigate operator mixing effects. Both the
Jaffe-Manohar as well as the Ji quark spin-orbit correlations are
extracted, yielding evidence for a strong quark spin-orbit coupling
in the proton.
