Bulletin of the American Physical Society
2017 Fall Meeting of the APS Division of Nuclear Physics
Volume 62, Number 11
Wednesday–Saturday, October 25–28, 2017; Pittsburgh, Pennsylvania
Session 1WB: Theoretical Approaches to Hadron Structure 
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Chair: Colin Morningstar, Carnegie Mellon University Room: Marquis B 
Wednesday, October 25, 2017 9:00AM  9:30AM 
1WB.00001: Hadron structure from lattice QCD Invited Speaker: Martha Constantinou More than 99 per cent of the mass of the visible world resides in hadrons which are bound states of quarks and gluons, the fundamental constituents of Quantum Chromodynamics (QCD). The proton is at the heart of the hadronic matter and is an ideal laboratory for studying the QCD dynamics. Lattice QCD (LQCD) is a powerful nonperturbative tool for the ab inition calculation of hadron observables that are well determined experimentally, or not easily accessible in experiment. Progress in the simulation of LQCD has been impressive, mainly due to improvements in the algorithms, development of new techniques 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 developments in hadron structure focusing on achievements in the evaluation of nucleon quantities, such as the nucleon charges, form factors, and gluonic contributions, in view of simulations close or at the physical value of the pion mass. I will also discuss the enormous efforts towards a new direct approach to compute quark parton distributions functions on the lattice. [Preview Abstract] 
Wednesday, October 25, 2017 9:30AM  10:00AM 
1WB.00002: Amplitude analysis for exotic states Invited Speaker: Alessandro Pilloni Last decade witnessed a proliferation of new exotic states, in particular in the heavy quark sector. A comprehensive picture of all these states remains an unsettled topic. We discuss the issues of the amplitude analyses related to the exotic states. With the specific example of the $Z_c(3900)$, we show how this can help in distinguishing the possible scenarios of a proper state, or a kinematical enhancement. [Preview Abstract] 
Wednesday, October 25, 2017 10:00AM  10:30AM 
1WB.00003: Nucleon Polarisabilities and Effective Field Theories Invited Speaker: Harald W. Griesshammer Lowenergy Compton scattering probes the nucleon's twophoton response to electric and magnetic fields at fixed photon frequency and multipolarity. It tests the symmetries and strengths of the interactions between constituents, and with photons. For convenience, this energydependent information is often compressed into the two scalar dipole polarisabilities $\alpha_{E1}$ and $\beta_{M1}$ at zero photon energy. These are fundamental quantities, and important for the proton charge radius puzzle and the Lamb shift of muonic hydrogen. Combined with emerging lattice QCD computations, they provide stringent tests for our understanding of hadron structure. Extractions of the proton and neutron polarisabilities from all published elastic data below 300~MeV in Chiral Effective Field Theory with explicit $\Delta(1232)$ are now available. % This talk emphasises $\chi$EFT as natural bridge between lattice QCD and ongoing or approved efforts at HI$\gamma$S, MAMI and MAXlab. Chiral lattice extrapolations from $m_\pi>200$~MeV to the physical point compare well to lattice computations. Combining $\chi$EFT with highintensity experiments with polarised targets and polarised beams will extract not only scalar polarisabilities, but in particular the four sofar poorly explored spinpolarisabilities. These parametrise the stiffness of the spin in external electromagnetic fields (nucleonic birefringence/Faraday effect). New chiral predictions for proton, deuteron and ${}^3$He observables show intriguing sensitivities on spin and neutron polarisabilities. Data consistency and a modelindependent quantification of residual theory uncertainties by Bayesian analysis are also discussed. % Protonneutron differences explore the interplay between chiral symmetry breaking and shortdistance Physics. Finally, I address their impact on the neutronproton mass difference, bigbang nucleosynthesis, and their relevance for anthropic arguments. [Preview Abstract] 
Wednesday, October 25, 2017 10:30AM  11:00AM 
1WB.00004: COFFEE BREAK

Wednesday, October 25, 2017 11:00AM  11:30AM 
1WB.00005: Nucleon Elastic and Transition form factors from the DysonSchwinger Equations Invited Speaker: Ian Cloet Recent progress in the boundstate problem in continuum QCD has produced a consistent treatment of the nucleon and its resonances. These studies predict the presence of strong diquark correlations within baryons, whose impact on the nucleon elastic and transition form factors will be illustrated. For example, the Roper resonance is found to be the nucleon's first radial excitation and consists of a core of three dressedquarks whose charge radius is 80\% larger than the proton analogue. This core is complemented by a meson cloud which reduces the observed Roper mass by about 20\%, however the quark core is revealed to probes with $Q^2 > 3 M_N^2$. [Preview Abstract] 
Wednesday, October 25, 2017 11:30AM  12:00PM 
1WB.00006: Hadron electric polarizability from lattice QCD Invited Speaker: Andrei Alexandru Electromagnetic polarizabilities are important parameters for hadron structure, describing the response of the charge and current distributions inside the hadron to an external electromagnetic field. For most hadrons these quantities are poorly constrained experimentally since they can only be measured indirectly. Lattice QCD can be used to compute these quantities directly in terms of quark and gluons degrees of freedom, using the background field method. We present results for the neutron electric polarizability for two different quark masses, light enough to connect to chiral perturbation theory. These are currently the lightest quark masses used in polarizability studies. For each pion mass we compute the polarizability at four different volumes and perform an infinite volume extrapolation. We also discuss the effect of turning on the coupling between the background field and the sea quarks. [Preview Abstract] 
Wednesday, October 25, 2017 12:00PM  12:30PM 
1WB.00007: Quarkonium as relativistic bound state on the light cone Invited Speaker: Yang Li I will review recent results for mesons obtained within a lightfront Hamiltonian approach [1,2]. We adopt a QCD inspired effective Hamiltonian that incorporates a holographic QCD confining potential at large distance and a onegluon exchange at short distance. The model is then solved by a basis function approach. \newline\newline We apply this model to charmonium and bottomonium. The masses agree with experiments to within an rms deviation of 40 MeV. The obtained lightfront wave functions provide a direct access to hadronic observables, e.g., decay constants, form factors and radii, as well as lightcone distributions, such as the distribution amplitudes and parton distributions, which reveals rich structural information of the hadrons, especially for the excited states. The wave functions also find application to diffractive productions in deep inelastic scattering. \newline\newline Comparison with experiments and other approaches show that our model provides an overall reasonable description of the heavy quarkonia. \newline\newline [1] Y.~Li, P.~Maris, X.~Zhao and J.P.~Vary, %``Heavy Quarkonium in a Holographic Basis,'' Phys.~Lett.~B {\bf 758}, 118 (2016); % doi:10.1016/j.physletb.2016.04.065 [arXiv:1509.07212 [hepph]]. \newline [2] Y.~Li, P.~Maris and J.~P.~Vary, %``Quarkonium as relativistic bound state on the light front,'' Phys.~Rev.~D (in press); [arXiv:1704.06968 [hepph]]. [Preview Abstract] 
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