Undergraduate Research at Jefferson Lab

The Unpolarized Transverse Momentum Dependent Distributions from JLab6 Data

Student: Mo Niazi

School: The University of Oklahoma

Mentored By: Wally Melnitchouk, Alexei Prokudin and Nobuo Sato

The quark structure of the nucleon is one of the main areas of research in modern nuclear physics. Historically only the information on the momentum fraction of the nucleon's longitudinal momentum carried by partons was accessed in the deep inelastic scattering (DIS) experiments. Parton distribution functions (PDFs) and fragmentation functions (FFs) have been extensively studied and libraries of parametrizations of PDFs extracted from experimental data are accessible. The Semi-Inclusive Deep Inelastic Scattering (SIDIS) experiments and measurements of differential cross sections in terms of transverse momentum dependence (TMD) of the produced hadron allow for the construction of TMDPDFs and TMDFFs that will lead to new insights into the structure of the nucleon. Novel theoretically proposed TMDPDFs and TMDFFs will be needed to construct similar libraries for TMD cross-section calculations. The goal of this project consisted of analyzing, and fitting the unpolarized JLab6 SIDIS experimental data to proposed Gaussian based models for TMDPDFs and TMDFFs. The fitting, data analysis, and error analysis was conducted using Python. The least squares method was invoked for the fits, pylab imported packages for the creation of plots, and the error analysis was done using a Monte Carlo simulation with randomized initial conditions. Initial results for the parameterization and minimization of the TMDPDFs and the TMDFFs resulted in improvements on reported literature values. Furthermore, the proposed Gaussian models were able to fit both sets of data with Χ2 values of 1.47 and below. Monte Carlo error analysis on the JLab6 data revealed that approximately 20,000 fits failed to generate statistically distinct parameter values. This led us to conclude that the JLab6 data lacked the proper resolution to be analyzed for TMD fitting parametrizations. Future experiments with JLab12 will be essential for the advancement of TMD phenomenology research.