Speaker
Michael Engelhardt
(New Mexico State University)
Description
Quark orbital angular momentum (OAM) in the proton can be calculated
directly if a Wigner function encoding the simultaneous distribution
of quark transverse positions and momenta is given. This distribution
can be accessed via proton matrix elements 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). Consequently, to generate the weighting by quark transverse
position needed to calculate OAM, a derivative with respect to momentum
transfer is required. A Lattice QCD calculation is presented in which
this derivative is evaluated using a direct derivative method, i.e., a
method in which the momentum derivative of a correlator is directly
sampled in the lattice calculation, as opposed to extracting it a
posteriori from the numerical correlator data. The method removes the
bias stemming from estimating the derivative a posteriori that was
seen to afflict a previous exploratory calculation. Data for Ji OAM
generated on a clover ensemble at 317 MeV pion mass are seen to agree
with the result obtained via the traditional Ji sum rule method. By
varying the gauge connection in the quark bilocal operator, also
Jaffe-Manohar OAM is extracted, and seen to be enhanced significantly
compared to Ji OAM.
Primary author
Michael Engelhardt
(New Mexico State University)
