[Theory-seminars] Theory Seminar, Friday Aug 4, 2:30pm, Room F224-225 - Ridge Liu and Harvey Shows

[Alessandro Pilloni]

Dear all,
we will have two seminars this friday
by two summer students.

Theory Center Seminar
Friday, August 4
1:00pm
CEBAF Center, Room F224-225

*Ridge Liu (Rice U.)
**Meson loop corrections to nucleon properties
* 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.

*Harvey F. Shows III (LSU)**
*
*Global QCD Analysis of the Nucleon Tensor Charge with Lattice QCD 
Constraints*
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.


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