Bulletin of the American Physical Society
82nd Annual Meeting of the APS Southeastern Section
Volume 60, Number 18
Wednesday–Saturday, November 18–21, 2015; Mobile, Alabama
Session L2: Nuclear Physics IV |
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Chair: Ralph France III, Georgia College & State University Room: Riverview Plaza Hotel Mobile Bay Ballroom I |
Saturday, November 21, 2015 8:30AM - 9:06AM |
L2.00001: Application of Virtuality Distribution Formalism to Pion Transition and Electromagnetic Form Factors Invited Speaker: Anatoly Radyushkin We discuss two applications of the Virtuality Distribution Amplitudes (VDA) formalism developed in our recent papers. We outline first the basic concepts of the VDA approach and introduce the pion transverse momentum distribution amplitude (TMDA) which plays, in a covariant Lagrangian formulation, a role similar to that of the pion wave function in the 3-dimensional Hamiltonian light-front approach. Then we propose simple factorized models for soft TMDAs, and use them to describe existing data on the pion transition form factor, thus fixing the scale determining the size of the transverse-momentum effects. Finally, we apply the VDA approach to the one-gluon exchange contribution for the pion electromagnetic form factor. In our model, we observe a very late $Q^2 > 20$ GeV$^2$ onset of transition to the asymptotic pQCD predictions and show that in the $Q^2 < 10$ GeV$^2$ region there is essentially no sensitivity to the shape of the pion distribution amplitude. Furthermore, the magnitude of the one-gluon exchange contribution in this region is estimated to be an order of magnitude below the Jefferson Lab data, thus leaving the Feynman mechanism as the only one relevant to the pion electromagnetic form factor behavior for accessible $Q^2$. [Preview Abstract] |
Saturday, November 21, 2015 9:06AM - 9:18AM |
L2.00002: Deuteron Momentum Distributions William Ford, Sabine Jeschonnek, J. Wallace Van Orden A primary goal of deuteron electrodisintegration is determining the momentum distribution. Due to the extensive model inputs that are required to describe this process, extracting the momentum distribution is fraught with difficulty. We present a method of investigating the momentum distribution by performing the extraction with a wide variety of model constituents including various wave functions, form factors, and final state interactions. This method provides a systematic way to investigate the distribution, and provides theoretical uncertainty due to model inputs. [Preview Abstract] |
Saturday, November 21, 2015 9:18AM - 9:30AM |
L2.00003: Partons Transverse Momentum and Orbital Angular Momentum Distributions Abha Rajan, Aurore Courtoy, Michael Engelhardt, Simonetta Liuti We discuss the two definitions of partonic orbital angular momentum given by Ji and by Jaffe and Manohar, respectively. While the former connects to the twist two Generalised Transverse Momentum Distribution $F_{14}$, the latter has been shown to connnect to the twist three Generalised Parton Distribution $G_2$. We demonstrate that the two definitions are infact related and differ essentially in their gauge link structure. Starting from nonlocal, $k_T$ unintegrated, off-forward matrix elements, instead of the standard Operator Product Expansion, we show how $G_2$ can be written as the sum of twist two, quark mass, and interaction dependent (twist three) terms, thus emphasizing the role of quark intrinsic transverse momentum and off-shellness. The twist two term in particular is given by the $k^2_T$ moment of $F_{14}$. We therefore uncover a relation/sum rule connecting the two definitions of orbital angular momentum, $F_{14}$ and $G_2$. We explore both the spin and the intrinsic transverse momentum/transverse space correlations as well as the gauge link structure behind the two decomposition frameworks, which are necessary to extract orbital angular momentum from experiment. [Preview Abstract] |
Saturday, November 21, 2015 9:30AM - 9:42AM |
L2.00004: Nuclear Fragmentation (I): Abrasion Cross Sections for Abrasion-Ablation Model William Ford, Charles Werneth, Khin Maung, Wouter DeWet, Lawrence Townsend In order to understand the radiation dose delivered to astronauts behind shielding, accurate nuclear fragmentation cross sections are required as input to transport codes. The fragmentation process can be divided into two steps; a fast step, abrasion, and a slow evaporation step, ablation. This talk will focus on the abrasion cross section which can be calculated by the Eikonal phase function. We present a calculation for the abrasion cross sections based on an optical potential model derived in a multiple scattering series. Preliminary results will be presented. [Preview Abstract] |
Saturday, November 21, 2015 9:42AM - 9:54AM |
L2.00005: Nuclear Fragmentation (II): Ablative Evaporation for Abrasion-Ablation Model Wouter de Wet, William Ford, Lawrence Townsend, Charles Werneth, Khin Maung One of the many potentially limiting factors for extraterrestrial operations involving manned missions is the dose received by crew in the harsh space radiation environment. In order to sufficiently understand the radiation dose delivered to astronauts behind shielding, the radiation transport codes used to calculate these doses require accurate nuclear fragmentation cross sections. The fragmentation process can be divided in to two steps: a fast step (abrasion), and a slower evaporation step (ablation). This talk will focus on the ablation cross section, which is calculated by a Monte Carlo process via the updated evaporation code EVA based on Dostrovsky et. al. Phys. Rev. 116, 683 (1959). The code has been updated and completely modernized. Efforts are under way for potential improvements to the model and preliminary results will be presented. [Preview Abstract] |
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