Bulletin of the American Physical Society
2007 Annual Meeting of the Division of Nuclear Physics
Volume 52, Number 10
Wednesday–Saturday, October 10–13, 2007; Newport News, Virginia
Session JE: Hadronic Systems |
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Chair: M. J. Ramsey-Musolf, California Institute of Technology Room: Newport News Marriott at City Center Grand Salon V |
Saturday, October 13, 2007 2:00PM - 2:12PM |
JE.00001: Global Fit to the Nucleon Strange Electromagnetic Form Factors Jianglai Liu, Michael J. Ramsey-Musolf, Robert D. McKeown The strange electric and magnetic form factors of the nucleon, $G_{E}^s$ and $G_M^s$, give the contributions of strange quarks to the charge and magnetization distributions of the nucleon, which solely arise from the sea of $s\bar s$. $G_E^s$ and $G_M^s$ can be determined by combining the well-known electromagnetic form factors of the proton and the neutron, $G_{E,M}^{\gamma,p}$ and $G_{E,M}^{\gamma,n}$, with the neutral weak form factors of the proton, $G_{E,M}^{Z,p}$, which can be measured via parity-violating (PV) elastic electron scattering. In the past 10 years, a series of definitive PV electron scattering experiments along with several theoretical studies now provide a basis for extracting precision information on these strange quark contributions. In this talk, we report the results of a global analysis of all these experiments, including both the latest data obtained in experiments performed at the Jefferson Laboratory and appropriate theoretical input on radiative corrections, and obtain values for the strange electric and magnetic form factors of the nucleon at a four-momentum transfer $Q^2 = 0.1$~GeV/$c^2$. [Preview Abstract] |
Saturday, October 13, 2007 2:12PM - 2:24PM |
JE.00002: Strangeness Contributions to the Static Properties of the Proton Kent Paschke Precision measurements of parity violation in electron-nucleus elastic scattering at low $Q^2$ are sensitive to the strange quark magnetic moment and the strange-charge radius of the proton, and thus provide a unique opportunity to cleanly isolate the role of the quark- antiquark sea in low-energy Quantum Chromodynamics. While recent results have placed a tight upper-bound on strange quark contributions to the electric form-factor at low $Q^2$, significant ($\sim$10\%) contributions to the proton magnetic moment are still allowed by the existing data. Results from recently completed measurements of backward-angle scattering, by the G0 and A4 collaborations, will provide an improved sensitivity to the strange magnetic form-factor $G_M^s$ of the proton as well as to axial radiative corrections which are otherwise poorly constrained by existing data. An important complement to those measurements is the HAPPEX-III experiment, which will measure forward-angle scattering at $Q^2 \sim 0.62$~GeV$^2$ with a much greater precision than has previously been achieved in that kinematic range, with a sensitivity to the linear combination of strange-quark vector form- factors $G_E^s + 0.48\,G_M^s$. In combination with the published results from low $Q^2$, this measurement will play a crucial role in determining the possible strange quark contribution to the magnetic moment of the proton. [Preview Abstract] |
Saturday, October 13, 2007 2:24PM - 2:36PM |
JE.00003: Parity-Violating Asymmetry in the Nucleon to Delta Transition C.L. Capuano The G$^0$ collaboration at Jefferson Lab has taken data on the parity-violating asymmetry for the inelastic scattering of electrons from the proton. Data were obtained for inclusive pion electroproduction at two beam energies (362 MeV and 687 MeV), with the scattered electrons detected at backward angle ($\theta_e' \sim 110^{\circ}$). These data will be used to extract the axial vector transition form factor $G^A_{N\Delta}$ as a function of $Q^2$ for $ 0.05 \; {\rm GeV/c}^2< Q^2 < 0.5 \; {\rm GeV/c}^2$. $G^A_{N\Delta}$ characterizes the intrinsic spin response of the nucleon during its transition to its first excited state. This experiment represents the first determination of this quantity using a neutral current probe. Data obtained with a deuterium target will also be studied. The status of the data analysis for both hydrogen and deuterium will be presented. [Preview Abstract] |
Saturday, October 13, 2007 2:36PM - 2:48PM |
JE.00004: Exclusive Electroproduction of the $\pi^0$ Meson off of the Nucleon Anthony Villano Nucleon transition amplitudes offer insight into the transition between hadronic degrees of freedom and quark-gluon degrees of freedom. Since many resonant excitations of the nucleon couple strongly to single pion production, one can hope to probe the interesting transition region through pion production measurements. A study of $\pi^0$ production from a nucleon target at $Q^2$ of 6.4 and 7.7 GeV$^2$ has recently been undertaken by the Jefferson lab Hall C collaboration. The differential cross sections can be used to constrain excitation form factors $G^\star_M$ and several multipole transition amplitudes for the lowest lying nucleon excitation, the $\Delta(1232)$ resonance. Differential cross sections as they relate to both non-resonant processes and resonance excitations will be discussed. Information on the excitation form factors and multipole amplitudes will be presented along with the implications of various theoretical predictions. [Preview Abstract] |
Saturday, October 13, 2007 2:48PM - 3:00PM |
JE.00005: Vector Meson Form Factors and Wave Functions from Holographic QCD. Hovhannes Grigoryan, Anatoly Radyushkin Based on the holographic dual model of QCD, we study 2- and 3-point functions of vector currents and derive form factors as well as wave functions for the vector mesons. As a result, generalized vector-meson dominance representation for form factors is obtained with a very specific VMD pattern. The calculated electric radius of the rho-meson is shown to be in a good agreement with predictions from lattice QCD. [Preview Abstract] |
Saturday, October 13, 2007 3:00PM - 3:12PM |
JE.00006: Gluelump Spectrum on Coulomb Gauge QCD Peng Guo, Adam Szczepaniak, Andrea Vassallo, Giuseppe Galata, Elena Santopinto We compute the energy spectrum of low-lying gluonic excitations in the presence of static quark-antiquark octet color sources at zero separation using Coulomb gauge and the quasi-particle representation. The states also refer to gluelump states. We will show how does many-body interactions from non-abelian Coulomb kernel generate correct ordering of spectrum for spin-parity-charge conjugation multiplets. [Preview Abstract] |
Saturday, October 13, 2007 3:12PM - 3:24PM |
JE.00007: A New Picture of Structure of Meson Bing An Li Quark model and parton model are the two models of hadrons. In this talk a unified model of meson structure is presented. Based on current algebra and chiral symmetry a chiral field theory of pseudoscalar, vector, axial-vector mesons is constructed. Both constituent and current quark masses appear in the same theory. Quark condensation, $N_C$ expansion, and chiral symmetry are embedded. Besides three current quark masses there are two parameters. The theory is phenomenologically successful. A brief review of the achievements is presented. In this talk we emphasize the new picture of the structure of pion. $m^2_\pi$ is derived. Pion form factor is predicted, which is in excellent agreement with data in both space-like and time-like regions. A new asymptotic pion form factor $F(Q^2)|_{Q^2\rightarrow\infty}$ is obtained. The pion structure is revealed: \begin{enumerate} \item when $q^2 < m^2_\rho$ pion is made of a pair of constituent quarks: $q\bar{q}$ \item when $q^2 > m^2_\rho$ pion is made of a pair of constituent quarks plus $\rho$ cloud multi- quark pairs \item at large $q^2$ pion is made of a pair of constituent quarks plus a hard gluon \end{enumerate} Similar structures for kaons and other mesons are presented. [Preview Abstract] |
Saturday, October 13, 2007 3:24PM - 3:36PM |
JE.00008: Fermilab E906: Extension to High-X of Measurement of the Anti-quark Distributions of Nuclei and Nucleons Donald Isenhower The quark-level structure of the nucleon has been studied by various methods. Fixed-target Drell-Yan scattering can kinematically select events that specifically probe the target's antiquark distributions and is ideally suited to study these effects. Fermilab E906, which was approved by Fermilab in 1999, after the completion of Fermilab E866/NuSea in 1997, has recently been given permission to proceed with construction of the experiment. E866/NuSea yielded a number of important physics results, including total proton-proton cross sections, energy loss measurements, and the first measurement of the cross section ratio of proton-proton to proton-deuterium collisions over a large kinematic range, allowing the extraction of the ratio of anti-down to anti-up quarks in the proton. E906 will take advantage of the lower energy of the Fermilab Main Injector to extend the range of the E866/NuSea measurements to larger Bjorken-x to further the search for changes in the sea quark distributions in nuclei. The apparatus to be used will be discussed, along with the many studies for optimizing the experiment. [Preview Abstract] |
Saturday, October 13, 2007 3:36PM - 3:48PM |
JE.00009: Quark Model of Heavy Baryons Muslema Pervin, Winston Roberts We use a nonrelativistic quark model to examine the spectrum of heavy baryons. The model provides a good description of the known states in the heavy $\Lambda_Q$, $\Sigma_Q$ and $\Omega_Q$ spectra, and it successfully predicts, without fitting, a number of states recently seen. When applied to the heavy cascade ($\Xi_Q$) spectrum, the model can be used to determine the sextet-antitriplet mixing in the known states. We briefly discuss some aspects of this mixing. This work is supported by the U. S. Department of Energy, Office of Nuclear Physics, under contract No. DE-AC02-06CH11357. [Preview Abstract] |
Saturday, October 13, 2007 3:48PM - 4:00PM |
JE.00010: Search for $\Phi(1862)$ Pentaquark States with CLAS Hovanes Egiyan Following the first observations of the possible $S=+1$ pentaquark state $\Theta^{+}(1540)$, there have been many experiments in various laboratories to confirm these results and to search for states which could be associated with other members of the pentaquark antidecuplet. The NA49 collaboration reported the observation of narrow $S=-2$ states with masses about $1860$~GeV showing in the $\Xi \pi$ invariant mass spectra. These states were identified as isospin $3/2$ members of the pentaquark antidecuplet, and were named $\Phi(1862)$. However, other experiments have failed to reproduce these results. A new experiment has recently been performed at Jefferson Lab using the CLAS detector to search for the $\Phi(1862)$ state in photoproduction on a deuterium target. A large amount of data has been collected and analyzed, and approximately two thousand $\pi^{-} \Xi^{-}$ events were identified. The preliminary invariant mass spectrum of the $\pi^{-} \Xi^{-}$ system, where the $\Phi^{--}(1862)$ pentaquark state is expected, will be presented and discussed. [Preview Abstract] |
Saturday, October 13, 2007 4:00PM - 4:12PM |
JE.00011: Precision fragmentation function measurements at Belle Martin Leitgab In order to precisely measure the gluon polarization in inclusive hadron production at RHIC and in semi-inclusive DIS good knowledge of the unpolarized fragmentations is necessary. As most of the world data on fragmentation functions has been obtained at LEP energies, especially the gluon fragmentation function is poorly known. The Belle experiment at KEKB in Japan has a large amount of data from which fragmentation functions can be extracted at relatively low scale with high precision. In addition also spin dependent fragmentation functions, such as the Collins function and the interference fragmentation function can and partially have been obtained from this data. Those fragmentation functions are important to extract the transverse quark spin polarization at RHIC and in semi-inclusive DIS. The current status of the analysis will be presented. [Preview Abstract] |
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