Session J15: Hadron Structure II

The Search For Nucleon-Nucleon Correlations and the EMC Effect

Many experiments, using different reaction channels as well as different beams, have shown evidence for two-nucleon tensor and short-range correlations in nuclei. Far more elusive has been isolating three-nucleon correlations. The current discrepancy between the xB>2 inclusive experiments that are searching for three-nucleon correlations will be discussed and a possible solution to the discrepancy presented. It will also be shown how the kinematic reach of an electron ion collider (EIC) may be required to finally isolate the signature of three-nucleon correlations as well as how an EIC would be used to further study how short-range initial-state correlations effect deep inelastic scattering results.   

Quark/gluon structure of light nuclei with spectator tagging at EIC

Exploring the quark/gluon structure of nuclei is a key objective of QCD-based nuclear physics. Nuclear modifications of the parton densities arise from the effect of the nuclear medium on single-nucleon structure at large x (EMC effect) and the possibility of coherent scattering from multiple nucleons at x $\ll$ 0.1 (shadowing). An Electron-Ion Collider (EIC) would enable next-generation measurement of deep-inelastic scattering from polarized light nuclei (deuteron, 3He) over a wide kinematic range, with detection of forward-moving spectator nucleons (spectator tagging). We report about results of an R\&D project simulating such measurements and quantifying their physics impact. This includes (a) controled measurements of the EMC effect in the deuteron as a function of the recoil proton momentum; (b) final-state interactions in nuclear scattering; (c) novel detailed studies of shadowing in tagged DIS at small x   

Coherent $\rho$-meson photo production from CLAS

Coherent $\rho$ photoproduction from the deuteron has been studied at CLAS as a function of the photon energy and the 4-momentum transfer. Tagged photons with beam energies between 0.8 and 3.0 GeV were produced using the bremsstrahlung process at Hall B of Jefferson Lab, incident on a deuterium target, during the run period g10. The final state particles detected are an energetic deuteron and a pair of charged pions from the $\rho^0$ meson decay. These events were constrained to have zero missing mass, to ensure an exclusive reaction. Preliminary cross sections have been obtained from fits to the $\rho$ peak in the invariant mass spectrum of the $\pi^+\pi^-$ pair for bins in the 4-momentum transfer $t$ as a function of $E_\gamma$. These data are important to test models of hadronic scattering of $\rho$ mesons from the nucleon, as it is not possible to produce beams of $\rho$ mesons. In addition, this study is also important to understand the backgrounds in analyses of a possible $d^*$ dibaryon resonance that has the same final state.   

Meson Spectroscopy in Coherent Production off $^4$He with CLAS

Meson spectroscopy requires disentanglement of states with different quantum numbers that decay to the same final states, as well as separation of meson-bayron and purely mesonic states. Coherent scattering off $^{4}$He uniquely aids both by providing a spin and iso-spin zero target, simplifying partial wave analysis, and an unmodified recoil nucleus, eliminating background from bayron resonances . At Jefferson Lab, we conducted the first experiment for meson spectroscopy using coherent quasi-real photo-production on $^{4}$He. This took place in Hall-B in 2009, using a 6 GeV electron beam and the CLAS detector. A new radial time projection chamber with high pressure gaseous target detects low-energy recoil $^{4}$He nuclei. In this talk, status of the analysis and the first look on coherently produced mesonic final states will be presented.   

The Scalar Generalized Transverse Momentum Distributions

We present a calculation of the scalar twist-3 Generalized Transverse Momentum Distributions (GTMDs) in the diquark model. Their TMD limit, e(x), can be accessed through the combined analysis of data for the sin $\phi$ -moment of the beam-spin asymmetry for di-hadron Semi-Inclusive DIS at Jefferson Lab, and from the semi-inclusive production of two hadron pairs in back-to-back jets in $e^+e^-$ annihilation at Belle. The scalar GTMDs, while allowing us to access quark-gluon correlations, are important because of their connection through integration with the pion-nucleon $\sigma$ term, giving the order parameter of spontaneous chiral symmetry breaking in the nucleon.   

QCD Nuclear g-factor and the Spin-Statistics Theorem

Consideration of the composite three-quark nucleon spin structure and its Pauli spin-statistics follows a new QCD g-factor with implications for the magnetic dipole moments of nucleons and their form factors. The reformulation of the nucleon magnetic moments using the new QCD nucleon g-factor is shown to be in striking agreement with global polarized and unpolarized e-p scattering data using the Sachs electric and magnetic form factors, thus reconciling long standing discrepancies between measurements. Additionally, the introduction of QCD isospin symmetry breaking (ISB) strange quarks terms contained within the meson-baryon exchange currents allow the partially conserved EM axial currents to be restored as well as providing a precise measure of the strange quark probabilities of the nucleons.   

The Checkerboard Model of the Nucleus

The Checker Board Model (CBM) of the nucleus and the associated extended standard model predicts that nature has 5 generations of quarks not 3 and that Nucleus is 2 dimensional. The CBM theory began with an insight into the structure of the He nucleus around the year 1989. Details of how this theory evolved which took many years, and is found on my web site (http://checkerboard.dnsalias.net) or in the following references \textbraceleft T.M. Lach, Checkerboard Structure of the Nucleus, Infinite Energy, Vol. 5, issue 30, (2000). \textbraceleft T.M. Lach, Masses of the Sub-Nuclear Particles, nucl-th/0008026, @http://xxx.lanl.gov/\textbraceright One independent check of this model is that the wavelength of the ``up'' quark orbiting inside the proton at 84.8123{\%} the speed of light (around the ``dn'' quark in the center of the proton) turns out to be exactly one de Broglie wavelength something determined after the mass and speed of the up quark were determined by other means. This theory explains the mass of the proton and neutron and their magnetic moments and this along with the beautiful symmetric 2D structure of the He nucleus led to the evolution of this theory. When this theory was first presented at Argonne in 1996, it was the first time that anyone had predicted the quarks orbited inside the proton at relativistic speeds and it was met with skepticism.