Bulletin of the American Physical Society
2012 Fall Meeting of the APS Division of Nuclear Physics
Volume 57, Number 9
Wednesday–Saturday, October 24–27, 2012; Newport Beach, California
Session FC: Hadron Physics I |
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Chair: Christine Aidala, University of Michigan Room: Plaza III |
Thursday, October 25, 2012 4:00PM - 4:12PM |
FC.00001: ABSTRACT WITHDRAWN |
Thursday, October 25, 2012 4:12PM - 4:24PM |
FC.00002: Deuteron Spin Structure function $g_1$ at low $Q^2$ Krishna Adhikari, Sebastian Kuhn The spin structure function $g_1(x,Q^2)$ and its moments provide crucial information on the internal structure of the nucleon. At low momentum transfer $Q^2$, one can study the transition from partonic (quark-gluon) to hadronic (nucleonic) degrees of freedom and test effective theories based on QCD, for instance Chiral Perturbation Theory (ChPT). As $Q^2$ goes to zero, the first moment of $g_1$ is constrained by the GDH sum rule and its ChPT extensions, which makes measurements of $g_1$ in this region uniquely interesting. As part of the large program of spin structure function measurements with CLAS at Jefferson Lab, the EG4 experiment measured the cross section difference between electron beam and proton/deuteron target spins parallel and antiparallel to each other (and the beam direction) down to small scattering angles (approx. 7 degrees). From these differences, $g_1$ can be extracted, with minimal model uncertainties, down to $Q^2$ as low as 0.01 GeV$^2$. We will give a brief overview of the experiment and its analysis, and present first preliminary results on the deuteron spin structure function $g_{1d}(x,Q^2)$. [Preview Abstract] |
Thursday, October 25, 2012 4:24PM - 4:36PM |
FC.00003: Parity-violating deep inelastic scattering with SoLID at Jefferson Lab Seamus Riordan Deep inelastic electron scattering has been an invaluable tool in understanding the internal structure of the nucleon and has provided motivation for the standard model of quarks and the concept of asymptotic freedom. When coupled with parity-violating measurements through the interference of a virtual photon and weakly interacting Z boson, new linear combinations of quarks are probed which can provide information which is complementary to the standard electromagnetic interactions. Precision measurements on deuterium allows for novel tests of the standard model, possible observations of quark-level charge symmetry violation, and the study of specific higher-twist effects. Additionally, measurements on a proton target can provide a precise extraction of the parton ratio $d/u$ as the Bjorken scaling variable $x \rightarrow 1$. Presented will be an approved experimental program at Thomas Jefferson National Accelerator Facility using the Solenoidal Large Intensity Device (SoLID) to study parity-violating deep inelastic scattering. [Preview Abstract] |
Thursday, October 25, 2012 4:36PM - 4:48PM |
FC.00004: A Preliminary Measurement of the Longitudinal Spin Asymmetry $A_1^{n}$ David Flay To date, measurements of the nucleon-virtual photon longitudinal spin asymmetry $A_1$ for both the proton and neutron have shown that the extracted helicity dependent-to-independent ratio of the down-quark parton distribution functions in the proton, $\Delta d/d$, tends towards -1/3 at large $x$, in disagreement with the perturbative QCD prediction that $\Delta d/d$ should approach unity. As part of Jefferson Lab experiment E06-014 performed in Hall A, double-spin asymmetries were measured when scattering a longitudinally polarized electron beam of energies 4.73 and 5.89 GeV from a longitudinally and transversely polarized $^3$He target in the deep inelastic scattering region, allowing for the extraction of the neutron asymmetry $A_1^n$. We will discuss the analysis of our data and present preliminary results for the nuclear asymmetry $A_1^{^3\textrm{He}}$ and $A_1^{n}$ in the kinematic range of $0.2 < x < 0.65$ and $2 < Q^2 < 5$ GeV$^2$ for the scattered electrons. Our measurement of $A_1^{n}$ will provide a test of previous results with a higher statistical precision and continuous coverage of the $x$ range above. [Preview Abstract] |
Thursday, October 25, 2012 4:48PM - 5:00PM |
FC.00005: Precision Measurement of the Neutron $d_{2}$ : A Probe of the Color Force Matthew Posik The $g_2$ nucleon spin-dependent structure function measured in electron deep inelastic scattering contains information beyond the simple parton model description of the nucleon. It provides insight into quark-gluon correlations and a path to access the confining local color force a struck quark experiences just as it is hit by the virtual photon due to the remnant di-quark. The quantity $d_2$, a measure of this local color force, has its information encoded in an $x^2$ weighted integral of a linear combination of spin structure functions $g_1$ and $g_2$ and is dominated by the valence-quark region at large momentum fraction $x$. To date, theoretical calculations and experimental measurements of the neutron $d_2$ differ by about two standard deviations. As a result, JLab experiment E06-014, performed in Hall A, made a precision measurement of this quantity. Double spin asymmetries and absolute cross-sections were measured in both DIS and resonance regions by scattering longitudinally polarize electrons at beam energies of 4.74 and 5.89 GeV from a longitudinally and transversely polarized $^3$He target. Preliminary results for the absolute cross-sections and spin structure functions on $^3$He will be presented as well as preliminary results for $d_2$ on $^3$He. [Preview Abstract] |
Thursday, October 25, 2012 5:00PM - 5:12PM |
FC.00006: Measurement of differential cross sections via $p(e,e^\prime \pi^+)n$ for studying high-lying resonances at high $Q^2$ Kijun Park, Volker Burkert An extensive experimental programs has been carried out at Jefferson Laboratory to study the excitation resonances using the CEBAF Large Acceptance Spectrometer (CLAS). Pion electroproduction on protons is sensitive to the resonance excitation and allows us to explore its internal structure. The CLAS is well suited for the study of a broad range of kinematics in the invariant mass $W$ and photon virtuality $Q^2$ with nearly complete angular coverage for the hadronic decays. Electron scattering allows us to probe the effective degrees of freedom in excited nucleon states from meson-baryon cloud to dressed quarks in terms of varying distance scale. In this talk, we report the differential cross-sections for exclusive single charged pion electroproduction from proton targets. The kinematic range covers $Q^2$ from $1.7\;\rm{GeV^2}$ to $4.5\;\rm{GeV^2}$ and $W$ from $1.6\;\rm{GeV}$ to $2.0\;\rm{GeV}$. Separated structure functions are also presented and compared with the present calculations and previous measurements. This work, along with an upcoming analysis of same kinematics from exclusive $p\pi^0$ and $p\pi^+\pi^-$ electroproduction will allow the determination of electro-couplings of several high-lying excited proton states, for the first time, at photon virtualities that correspond to transition toward dominance of quark degrees of freedom. [Preview Abstract] |
Thursday, October 25, 2012 5:12PM - 5:24PM |
FC.00007: First Measurements of the $\rho^1$, $\rho^2$, and $\rho^3$ Spin Density Matrix Elements in $\gamma p \rightarrow p\omega$ using CLAS at JLab Brian Vernarsky In an effort towards a ``complete'' experiment for the $\omega$ meson, we present studies from two experiments with unpolarized targets, one using a circularly polarized photon beam (g1c) and one using a linearly polarized photon beam (g8b), both carried out using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The experiments were analyzed using an extended maximum likelihood fit to the cross section with partial wave amplitudes. New likelihood functions were calculated to account for the polarization of the photon beams. The results of these fits are then used to project out the spin density matrix for the $\omega$. First measurements of the $\rho^1$, $\rho^2$, and $\rho^3$ spin density matrix elements will be presented using this method. As a check, we compare to another method, Schilling's method, which fits the decay angular distribution with a function that uses the spin density matrix elements as parameters. [Preview Abstract] |
Thursday, October 25, 2012 5:24PM - 5:36PM |
FC.00008: Pion Electroproduction and VCS in the Delta Resonance Region Nikolaos Sparveris The study of the N to $\Delta $ transition has been a subject of intense scientific interest for more than two decades. The pion electroproduction and VCS channels of the transition allow, through the measurement of the transition quadrupole amplitudes, the exploration for non-spherical angular momentum amplitudes in hadrons while the VCS channel also provides access to the nucleon polarizabilities. Results from JLab/Hall-A and MAMI will be presented and upcoming measurements will be discussed. [Preview Abstract] |
Thursday, October 25, 2012 5:36PM - 5:48PM |
FC.00009: Exclusive Kaon Electroproduction in Hall C at JLab 12 GeV and EIC Nathaniel Hlavin, Tanja Horn The additional flavor degree of freedom in the H($e,e^\prime K^+$)$\Lambda$/$\Sigma^0$ reactions provides a unique opportunity to study the mechanism underlying strangeness production and the transition from hadronic to partonic degrees of freedom in exclusive processes. However, due to the lack of experimental facilities, the potential of these reactions has not been fully exploited to date. The Jefferson Lab 12 GeV upgrade provides the energies needed for precision kaon cross section measurements in the valence quark region in Hall C. A new threshold aerogel Cerenkov detection system provides a simple and economical option for the kaon identification. Beyond the valence quark region, the first studies of strange sea quarks could be carried out at a future facility like an Electron Ion Collider (EIC). A Detector of Internally Reflected Cherenkov light (DIRC) offers a geometrically compact option for particle ID over the full range of kaon momenta. In this talk I will present the current status and discuss the outlook on future studies of strange quarks with kaon electroproduction as well as the particle identification requirements for each of these stages. [Preview Abstract] |
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