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<div>Dear all,<br>
we will have two seminars this friday<br>
by two summer students.<br>
<br>
Theory Center Seminar<br>
Friday, August 4<br>
1:00pm<br>
CEBAF Center, Room F224-225<br>
<br>
<b>Ridge Liu (Rice U.)<br>
</b><b>Meson loop corrections to nucleon properties<br>
</b>
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An asymmetry has been observed between the parton distribution
functions (PDFs) of the antiup and antidown quarks and between
those of the strange and antistrange quarks in a nucleon. One
possible explanation for the asymmetries is the effect of meson
loop diagrams on the 3-valence quark structure of the nucleon,
which arises from the chiral (left- vs. right-handed) symmetry
of the underlying Quantum Chromodynamics (QCD) theory. This
effect is quantifiable through splitting functions which
describe ways a photon probe can interact with a nucleon. The
focus of this study is to calculate the effect of one-meson-loop
diagrams on the self-energy of a nucleon and nucleon to meson +
baryon splitting functions using dimensional regularization
(DR), a method for regulating divergent integrals. We perform
multiple checks on the calculation, including finding the
leading nonanalytic behavior of the self-energy and splitting
functions and comparing against published results. Here we
present expressions for the self-energy and splitting functions
calculated using DR. We also show the consistency of the
calculations of the self-energy using DR with other
regularization methods. In contrast to other regularization
methods such as high-momentum cutoff, dimensional regularization
has the advantage of being manifestly covariant, i.e. respecting
Lorentz invariance. The expression for the splitting function
will allow for quantifying the magnitude of the meson loop
corrections to the PDFs, en route to explaining the
aforementioned observed asymmetries.
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<b>Harvey F. Shows III (LSU)</b><b><br>
</b>
<div><b>Global QCD Analysis of the Nucleon Tensor Charge with
Lattice QCD Constraints</b><br>
We understand matter by studying its constituents. Likewise,
by studying the parton distribution functions (PDFs) of a
nucleon, we probe the partonic scale of nature - exploring
what it means to be a nucleon. In this study, we are
interested in the transversity PDF. Being the least studied of
the three collinear PDFs, the transversity distribution is
poorly understood. By fitting experimental data from
semi-inclusive deep inelastic scattering (SIDIS), as well as
single-inclusive e+e- annihilation (SIA), we conduct a global
analysis and extract the fit parameters needed to describe the
transverse moment dependent (TMD) transversity PDF, as well as
the Collins Fragmentation Function. Once the collinear
transversity PDF is obtained by integrating the extracted TMD
PDF, we wish to resolve discrepancies between lattice QCD
calculations and phenomenological extractions of the tensor
charge from data. Here we show preliminary results for the
transversity function and tensor charge, obtained from a
global analysis of the current SIDIS and SIA data. In this
talk we outline an ongoing effort to extract the tensor charge
from the transversity PDF using maximum likelihood and nested
sampling methods. With this analysis, we are able to progress
in our understanding of TMD PDFs, as well as testify to the
efficacy of current lattice QCD calculations. </div>
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