Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session H15: Mini-Symposium: Short Range Nuclear Structure IIIFocus
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Sponsoring Units: DNP Chair: Or Hen, MIT Room: Sheraton Plaza Court 4 |
Sunday, April 14, 2019 10:45AM - 11:21AM |
H15.00001: Strength quenching in knockout reactions Invited Speaker: Daniel Bazin Knockout reactions have been used extensively with radioactive beams to explore the single-particle structure of rare isotopes. Combined with an eikonal model that takes into account the inclusive nature of the experimental data, proton and neutron removal knockout cross sections have been used to extract spectroscopic factors in nuclei with a wide range of separation energies. When compared to independent particle models, these spectroscopic factors exhibit a clear trend from the most weakly to the most deeply bound nucleons. This quenching evolution may have its origin in correlations absent from the truncated-basis shell-model calculations or in the approximations used in the reaction dynamics. The quenching observed from knockout reactions on rare isotopes is not compatible with results from transfer or proton-induced quasi-elastic scattering. Experiments have so far demonstrated the robustness of the assumptions made in the eikonal model. Direct comparison with cross sections calculated using ab initio structure models that include correlations may pave the way in disentangling reaction mechanism from structure effects. In this talk the status of these studies will be presented, followed by recent progress and future plans to tackle these issues. |
Sunday, April 14, 2019 11:21AM - 11:33AM |
H15.00002: Analyzing short-range correlations through the nonlocal dispersive optical model Mack C Atkinson, Willem H Dickhoff, Robert John Charity The presence of short-range correlations in nuclei leads to a population of nucleons with momentum greater than the nuclear Fermi momentum. This high-momentum content manifests in the tail of nucleon momentum distributions which can be calculated using a nonlocal dispersive optical model (DOM). We have generated DOM self-energies for three nuclei, $^{40}$Ca, $^{48}$Ca, and $^{208}$Pb. Using these self-energies, we explore how short-range correlations effect quantites such as particle number, neutron skin, and particle distributions, thereby providing insight as to how the role of short-range correlations varies with the size and asymmetry of nuclei. Furthermore, the existence of high-momentum content depletes the single-particle strength below the Fermi momentum. This effect is studied by calculating the spectroscopic factors from these DOM self-energies that reproduce $(e,e'p)$ momentum distributions. |
Sunday, April 14, 2019 11:33AM - 11:45AM |
H15.00003: The first fully exclusive SRC measurement in inverse kinematics using a 4 GeV/c/u 12C beam and a liquid hydrogen target Georgios Laskaris, Efrain Patrick Segarra The first fully exclusive SRC measurement using a 4 GeV/c/u 12C beam incident on a liquid hydrogen target was performed at JINR. This hard nucleon knock-out measurement took place in the inverse kinematics frame where all products of the hard knock-out reaction were detected in coincidence at the final state. In our talk, we will give a deep insight into how we study SRC pairs using inverse kinematics at JINR and the motivation for fully exclusive SRC measurements. We will present various experimental aspects as well as the first preliminary physics results of this recently executed measurement including the identified residual A-2 systems in coincidence to a proton from the SRC pair in the carbon nucleus and the target-scattered proton. |
Sunday, April 14, 2019 11:45AM - 11:57AM |
H15.00004: Investigating the EMC effect in highly-virtual nucleons at Jefferson Lab's Hall B Florian Hauenstein We installed a Backward Angle Neutron Detector (BAND) just upstream of the existing CLAS12 spectrometer at Jefferson Lab to detect high momentum neutrons at scattering angles between 160 and 170 degrees. These neutrons are spectators from electron-proton deep inelastic electron scattering (DIS) reactions in deuterium. The scattered electron is detected by CLAS12 while the recoiling neutron is detected by CLAS12 at intermediate angles or by BAND at backward angles, thereby ``tagging'' the DIS scattering off the proton in the deuteron. |
Sunday, April 14, 2019 11:57AM - 12:09PM |
H15.00005: A new comparison of the F2A/F2p and F2A/F2n structure function ratios Holly Szumila-Vance Using electron scattering data from SLAC E139 and muon scattering data from NMC in the deep-inelastic regime, we determine the F2A/F2p and F2A/F2n structure function ratios. These data span 0.07 ≤ xB ≤ 0.7 and 1 ≤ Q2 ≤ 200 GeV2/c2 and 0.006 ≤ xB ≤ 0.6 and 0.5 ≤ Q2 ≤ 55 GeV2/c2 for the SLAC and NMC data, respectively. This regime is of particular relevance to studies of the EMC Effect. We assume no Q2 dependence. We compare the structure function ratios for isoscalar nuclei and will look at the non-isoscalar nuclei with the possibility to look for flavor dependence. This talk will present the results of the comparison of the F2A/F2n and F2A/F2p structure function ratios for isoscalar nuclei using the new F2n global data set from the CTEQ-JLab Collaboration, and we compare these ratios with theoretical predictions. |
Sunday, April 14, 2019 12:09PM - 12:21PM |
H15.00006: A Non-perturbative Model of Mean Field Quarks Christopher A Leon, Misak M Sargsian We develop a non-perturbative model for valence quark distributions in the nucleon to account for the phenomena related to quark interactions in the mean field of the nucleon interior. The main motivation for the model is to obtain a mean field description of the valence quarks as a baseline upon which short range quark-quark interactions generate the high x tail of valence quark distributions. The model is based on the pionic cloud picture of the nucleon in which one assumes a factorization of the short-range valence quark and long range pion-cloud dynamics. The nucleon structure function is calculated using light-front dynamics and the effective Feynman diagrammatic approach is used to introduce valence quark and pion-cloud wave functions. The parameters of these wave functions are fixed by the position of the peak of xfq(x) distribution of valence quarks at Q0, corresponding to the charm-quark mass. With few parameters we achieved a very reasonable description of the up and down valence quark distributions in the moderate x region (x< 0.5) where one expects the mean field dynamics to dominate. The model however systematically underestimates the high x region, where we expect enhanced contribution from partonic correlations. |
Sunday, April 14, 2019 12:21PM - 12:33PM |
H15.00007: Experimental evidence for isospin dependence in the EMC effect John R Arrington, Nadia Fomin The observed correlation between the EMC effect and the relative contribution of SRCs in nuclei, combined with the observed np-dominance of high-momentum nucleon pairs, raises the question of whether the isospin dependence of SRCs yields an isospin-dependent EMC effect. The physics behind the EMC-SRC correlation, be it a common origin of both effects or SRCs as a source of the EMC effect, determines to what extend np-dominance of SRCs yields an isospin-dependent EMC effect. We examine existing data to look for observables that might be able to distinguish between different explanations for the observed correlation and address the question of isospin dependence in the EMC effect. |
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