Studying the Partonic Structure of the Nucleon by Means of the Beam Spin Asymmetry

Open Access
Banks, Daniel Paul
Area of Honors:
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Leonard P Gamberg, Thesis Supervisor
  • Richard Wallace Robinett, Honors Advisor
  • nuclear
  • physics
  • theoretical
  • quarks
  • nucleon
  • particle
  • scattering
  • parton
  • gluons
In our study we attempt to characterize the partonic structure of the nucleon via models of the beam-spin asymmetry observed in semi-inclusive deep inelastic scaterring experiments. In particular we are interested in calculating the parton distribution functions(PDF)g^perp and f_l^perp which model the intrinsic transverse momentum carried by up and down quarks in the case of unpolarized and longitudinally polarized beam-spins. We then use these PDFs to calculate the beam-spin asymmetry observed in π0 production. Our calculation of g^perp yields a negative value for all values of Bjorken x in the case of the up quark and positive values for all values of Bjorken x in the case of the down quark. This result implies that in this model calculation the SSA for π+ will be positive and π- will be negative. The comparison between our theoretical calculation and the data indicates that the D1 term can account for the beam SSA in π0 production measured by the CLAS Collaboration in the region x < 0.1 and PT < 0.2 GeV, where our theoretical curves describe the data reasonably well. Our study suggests that the T-odd twist-3 distribution g^perp plays an important role in the beam SSA in SIDIS, especially in the case of neutral pion production. In addition to our study on A_LU our investigation of A_UL is ongoing and could provide new information on the transverse structure and twist three content of nucleon structure.