Speaker
Michael Engelhardt
(NMSU)
Description
Quark orbital angular momentum (OAM) in the proton can be calculated
directly given a Wigner function encoding the simultaneous
distribution of quark transverse positions and momenta. 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). To generate the weighting by quark
transverse position needed to calculate OAM, a derivative with respect
to momentum transfer is consequently required. 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
(NMSU)