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Dear all,<br>
this is a reminder for today's seminar.<br>
<br>
Check the time, it's 1pm to avoid overlap with other lectures<br>
<br>
<div class="moz-cite-prefix">Il 01/08/2017 12:16, Alessandro Pilloni
ha scritto:<br>
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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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