Bulletin of the American Physical Society
APS April Meeting 2018
Volume 63, Number 4
Saturday–Tuesday, April 14–17, 2018; Columbus, Ohio
Session C05: From QCD to the DeuteronInvited Session
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Sponsoring Units: GFB DNP Chair: Dean Lee, Michigan State University Room: A123-125 |
Saturday, April 14, 2018 1:30PM - 2:06PM |
C05.00001: Lattice QCD and the gluonic structure of light nuclei Invited Speaker: Phiala Shanahan I will present the results of recent lattice QCD studies of aspects of the gluon structure of both hadrons and light nuclei. The generalised transversity gluon distributions are of particular interest since they are purely gluonic; they do not mix with quark distributions at leading twist. In light nuclei they moreover provide a clean signature of `exotic', i.e., non-nucleonic, gluon degrees of freedom. First QCD predictions for the magnitudes of these and other gluon structure quantities will be tested by experiments at Jefferson Laboratory, and at a future Electron-Ion Collider. [Preview Abstract] |
Saturday, April 14, 2018 2:06PM - 2:42PM |
C05.00002: New Results on the Nucleon Resonance Spectrum and Structure from Photo- and Electroproduction Experiments Invited Speaker: Victor Mokeev Studies of the excited nucleon ($N^{\ast })$ spectrum and structure offer unique information on many facets of strong QCD dynamics in the generation of resonances of different quantum numbers. Advances in nucleon resonance studies in experiments with electromagnetic probes will be presented. Experimental studies of meson photoproduction off the nucleon at the JLab/CLAS, ELSA, and MAMI facilities have provided detailed information on all exclusive meson photoproduction channels relevant in the resonance region. Analyses of these data have considerably extended our knowledge of the $N^{\ast }$ spectrum. Several candidate $N^{\ast }$ states were included in the PDG as an outcome of these efforts with critical impact of the strangeness photoproduction data from CLAS. Studies of the $N^{\ast }$-electroexcitation amplitudes \textbf{(}$\gamma_{v}$\textit{pN*} electrocouplings) at different photon virtualities $Q^{2}$ continue their rapid progress, offering insight into $N*$ structure. The CLAS detector at JLab has produced the dominant part of the data on meson electroproduction channels off the nucleon in the resonance region for $Q^{2}$ up to 5.0 GeV$^{\mathrm{2}}$. The $\gamma_{v}$\textit{pN}$^{\ast }^{\mathrm{\thinspace }}$electrocouplings have become available for most $N^{\ast }$ states in the mass range up to 1.8 GeV and $Q^{2}$ up to 5.0 GeV$^{\mathrm{2}}$. Physics analyses of these results have revealed the structure of $N*$ states as a complex interplay between an inner core of three dressed quarks and an external meson-baryon cloud. A successful description of the $\Delta $(1232)3/2$^{\mathrm{+}}$ and N(1440)1/2$^{\mathrm{+\thinspace }}$electroexcitation amplitudes starting from the QCD Lagrangian was achieved within the Dyson-Schwinger Equation (DSE) approach with the same momentum dependence of the constituent quark mass, offering sound evidence for the capability of exploring the dynamics of hadron mass generation. Independent analysis of the CLAS data on $N^{\ast }$ electroexcitations within the light front quark model has supported the running quark mass concept. Extension of the resonance electroexcitation studies with the CLAS12 detector will make it possible to explore $N^{\ast }$ structure at the highest photon virtualities ever achieved, from 5.0 GeV$^{\mathrm{2}}$ to 12 GeV$^{\mathrm{2}}$, addressing the most challenging problems on the nature of hadron mass and the emergence of quark-gluon confinement. In addition, the search for hybrid-baryons with glue as an active structural component will be carried out, completing the $N^{\ast } $spectrum exploration. [Preview Abstract] |
Saturday, April 14, 2018 2:42PM - 3:18PM |
C05.00003: Lattice Generalized Parton Distributions and Form Factors of the Nucleon Invited Speaker: Martha Constantinou Lattice QCD (LQCD) is a theoretical non-perturbative approach for the study of QCD dynamics numerically and from first principles. For more than a decade, LQCD has been very successful in the calculation of the hadronic spectrum, making postdictions of well-measured hadronic masses, as well as, predictions. Nowadays, LQCD is widely used for hadron structure calculations and is becoming a reliable tool, providing input to the experimental and phenomenological communities. Over the last years, progress in the simulation of LQCD has been impressive, driven by improvements in the algorithms and increase in computational power, that have enabled simulations to be carried out at parameters very close to their physical values. In this talk I will present recent results for the electromagnetic and axial form factors using simulations tuned to yield the physical value of the pion mass. Contributions from the valence and sea quark sector will be shown, including the light, as well as the strange and charm quarks. Our findings show non-negligible contributions from the sea quarks, which can be particularly large for certain form factors; this is in contrast to what was anticipated in the past. The high statistical accuracy of the calculation allows one to fit the momentum dependence of the electromagnetic form factors to extract the electric and magnetic radii of the proton and neutron. Similarly for the axial form factors the dipole masses are obtained and compared to experiment, which is of particular interest for neutrino physics. Finally, I will briefly discuss the progress in a new direct approach to compute quark parton distributions functions directly in LQCD. [Preview Abstract] |
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