[Theory-seminars] REMinDER: Theory Seminar, Friday Aug 4, ***1:00pm***, Room F224-225 - Ridge Liu and Harvey Shows

[Alessandro Pilloni]

Dear all,
this is a reminder for today's seminar.

Check the time, it's 1pm to avoid overlap with other lectures

Il 01/08/2017 12:16, Alessandro Pilloni ha scritto:
> 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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