Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session EG: Electromagnetic Interactions II |
Hide Abstracts |
Sponsoring Units: DNP JPS Chair: Dave Mack, Jefferson Lab Room: Ritz-Carlton Hotel Plantation 2 |
Wednesday, September 21, 2005 9:00AM - 9:15AM |
EG.00001: Double-Polarization Experiments Using Polarized HD at LEGS. C. Steven Whisnant A novel, solid, frozen-spin $H\!D$ target has been developed for
measurements of double-polarization observables in the $\Delta$
resonance region. Our focus is the determination of the pion
photo-production amplitudes for the neutron and proton. Cross
sections, beam asymmetries and the $E$ and $G$
double-polarization observables are measured simultaneously. $E$
provides information on the GDH and Spin-Polarizability spin sum
rule integrals. We report here a preliminary analysis of one
month of data collected on a $\vec{H}\!\vec{D}$ target with
polarizations of $ |
Wednesday, September 21, 2005 9:15AM - 9:30AM |
EG.00002: A Measurement of the Deuteron Magnetic Dipole Form Factor from Vector Polarization Observables Pete Karpius, John Calarco A measurement of the vector analyzing powers $T^{e}_{10}$ and $T^{e}_{11}$ and the magnetic dipole form factor $G_{M}$ in elastic electron-deuteron scattering has been conducted at the MIT-Bates Linear Accelerator Facility using a polarized electron beam, an internal polarized atomic deuterium target, and the symmetric BLAST(Bates Large Acceptance Spectormeter Toroid) detector in the Bates South Hall Ring. The beam helicity dependent target vector asymmetries, simultaneously measured in both sectors of BLAST, allow the extraction of $T^{e}_{10}$ and $T^{e}_{11}$. To our knowledge this is the first such use of a polarized target in measuring these observables. At low $Q^{2}$, the statistically more significant observable $T^{e}_{11}$ is dominated by the interference of $G_{M}$ and the charge monopole form factor $G_{C}$. The high accuracy to which $G_{C}$ is known in this region allows for the extraction of $G_{M}$ yielding the first such measurement of this kind from spin observables. Preliminary results for $T^{e}_{10}$, $T^{e}_{11}$, and $G_{M}$ will be presented. This work supported by DOE grants 181021 (UNH) and DEFC02-94ER40818 (MIT-Bates). [Preview Abstract] |
Wednesday, September 21, 2005 9:30AM - 9:45AM |
EG.00003: Recoil Polarization in Deuteron Photodisintegration Xiaodong Jiang High energy deuteron photodisintegration exhibits simple behaviors, including constant-angle cross sections that follow the constituent counting rules, for $p_T$ $>$ 1.3 GeV/$c$, and angular distributions that exhibit a slight asymmetry about $\theta_{\rm c.m.}$ $=$ 90$^{\circ}$. Measured recoil polarizations are small above 1 GeV, much smaller than hadronic model predictions, but not vanishing as predicted by helicity conservation. The limited 90$^{\circ}$ polarization data are insufficient to come to firm conclusions concerning the validity of several quark model predictions that are generally in agreement with the cross section data. We have taken new recoil polarization data, a five-point angular distribution at $E_{\gamma}$ $\approx$ 2 GeV. We will show the calibration $ep$ elastic scattering data agree with earlier results, the polarimeter performance agrees with expectation, and the $\vec{\gamma} d \to \vec{p} n$ data compared with model predictions. This work has been supported by the National Science Foundation, through grant PHY 03-54871 to Rutgers University. [Preview Abstract] |
Wednesday, September 21, 2005 9:45AM - 10:00AM |
EG.00004: $G_E^p/G_M^p$ with BLAST Adrian Sindile, John Calarco One of the experiments that recently finished running at the MIT Bates Lab is the measurement of the $G_E^p/G_M^p$ ratio, using a polarized electron beam, an internal polarized atomic hydrogen gas target and the symmetric BLAST (Bates Large Acceptance Spectrometer Toroid) detector in the South Hall Ring of the Bates Linear Accelerator Facility. We have used the super-ratio technique to extract the proton electric to magnetic form factor ratio for a $Q^2$ between 0.1 and 0.9 (GeV/c)$^2$ from two spin-dependent asymmetries we have measured simultaneously in the left and right sector of the BLAST detector respectively. This is the first time $G_E^p/G_M^p$ was measured using a polarized target. Preliminary results will be presented. DOE Grant Numbers: 181021 (UNH); DEFC02-94ER40818 (MIT Bates). [Preview Abstract] |
Wednesday, September 21, 2005 10:00AM - 10:15AM |
EG.00005: Medium modifications of nucleon structure functions Wolfgang Bentz, Ian Cloet, Anthony Thomas Using a chiral effective quark-diquark model for the single nucleon, we calculate the equation of state of nuclear matter in the mean field approximation, and the properties of a bound nucleon. In particular, we focus on the spin-independent and spin-dependent structure functions. For both cases, we first describe the free nucleon structure functions, and then consider the medium modifications. For the spin-independent case, we show the important role played by the mean vector field in the medium to explain the EMC effect. Concerning the spin-dependent case, we give predictions for the polarized EMC effect in the nuclear matter picture as well as for finite nuclei. [Preview Abstract] |
Wednesday, September 21, 2005 10:15AM - 10:30AM |
EG.00006: Nucleon electromagnetic form factors in nuclear matter. Tai Horikawa, Wolfgang Bentz We use the quark-diquark picture to construct the nucleon, and calculate its electromagnetic form factors. Furthermore, we estimate the medium effects for electromagnetic form factors by using the equation of state of nuclear matter in the mean field approximation. In this contribution, I explain the effect of the diquark intrinsic form factor, and the renormalization from the vector meson and pion cloud around the constituent quarks. [Preview Abstract] |
Wednesday, September 21, 2005 10:30AM - 10:45AM |
EG.00007: Comparison of the (e, e$'$p) cross sections at low momentum transfer on light nuclei with relativistic calculations Tadaaki Tamae The (e, e$'$p) cross sections have been measured on $^{12}$C, $^ {16}$O and $^{40}$Ca at an energy transfer of 60 MeV and low momentum-transfer around 105 MeV/c. The cross sections at missing momenta between 180 and 300 MeV/c obtained from the experiment are compared with theoretical calculations based on the relativistic distorted-wave impulse approximation (RDWIA) with and without meson exchange currents (MEC) made by Pavia group in Italy. The contribution of MEC due to the seagull currents is large in the high missing momentum region for $^ {12}$C in particular for the longitudinal component, while it is small on $^{16}$O and $^{40}$Ca. Current-conserving operators (cc1, cc2, cc3) are used in the theoretical calculation. It is known that they give large difference for the (${\gamma}$, p) reaction, while the difference is small for the quasi-elastic (e, e$'$p) reaction. Influence to the choice of the current operator is medium in the (e, e$'$p) reaction at low momentum transfer, but still large. The calculations overestimate the experimental cross sections by a factor of two in the low missing momentum region for all three nuclei. It indicates that some important ingredients are missing in the theoretical calculation. [Preview Abstract] |
Wednesday, September 21, 2005 10:45AM - 11:00AM |
EG.00008: Inclusive Scattering from Nuclei at x$>$1 and High $Q^2$ with a 6 GeV beam Nadia Fomin Inclusive electron scattering from nuclei at large $x$ and $Q^2$ is the result of a reaction mechanism that includes both quasi--elastic scattering from nucleons and deep inelastic scattering from the quark consitituents of the nucleons. Consequently, it provides an opportunity to investigate the transition from a regime where nucleon degrees of freedom dominate to one where the more fundamental QCD interactions are exposed. Data in this regime can be used to study a wide variety of topics, including the extraction of nuclear momentum distributions, the influence of final state interactions and the approach to $y$-scaling, the strength of nucleon-nucleon correlations, and the approach to $x$- scaling, to name a few. We recently peformed an experiment in Jefferson Lab's Hall C using a 6 GeV beam and a range of both light and heavy nuclei which was designed to significantly extend the kinematic region at high momentum transfer and large (negative) $y$, previously explored in SLAC experiment NE3 and Jefferson Lab experiment E89-008. After a brief statement of the physics goals of this experiment, we will present preliminary results. [Preview Abstract] |
Wednesday, September 21, 2005 11:00AM - 11:15AM |
EG.00009: New sum rules for the spin dependent structure functions $g_1$ Koretune Susumu Sum rules for the spin dependent structure function $g_1$ derived from the canonical quantization on the null plane have been regularized and transformed to the ones which are mainly concerned with the low energy quantities. These sum rules are related to the cross section of the photoproductions. Through these sum rules, it is discussed that there is a deep connection between the elastic and the resonance contributions, and that it is this relation which explains why the sign change discussed by the Drell Hern Gerasimov sum rule and Ellis Jaffe sum rule occurs in the very small $Q^2$ region. Thus the sum of these contributions can be related to the high energy behavior. [Preview Abstract] |
Wednesday, September 21, 2005 11:15AM - 11:30AM |
EG.00010: Resonant Spin Structure (RSS) of the Proton Karl Slifer Spin-dependent structure functions have been extracted from an inclusive doubly polarized asymmetry measurement at low momentum transfer ($Q^2\approx1.3 $GeV$^2$) in the resonance region. Longitudinally polarized electrons of incident energy 5.755 GeV were scattered from a polarized solid ammonia target in Jefferson Lab's experimental Hall C. Both NH$_3$ and ND$_3$ were used as target material giving access to the proton and deuteron spin structure respectively. For the first time at low $Q^2$ and in the resonance region, proton asymmetries were measured with both perpendicular and parallel target field orientation, allowing a precision determination of the spin structure functions g$_1$($x$,Q$^2$) and g$_2$($x$,Q$^2$). The $W-$dependence of the nucleon spin asymmetries $A_1(W,Q^2)$ and $A_2(W,Q^2)$ has been measured with high resolution, allowing for clear identification of individual resonance regions. Preliminary proton data will be presented which enable a test of local duality in the polarized structure functions. The moments of the spin structure functions, including the extended GDH sum and the $d_2$ matrix element, are also evaluated and compared with theoretical expectations. [Preview Abstract] |
Wednesday, September 21, 2005 11:30AM - 11:45AM |
EG.00011: Spin Structure Functions of the Deuteron in the Region of the Nucleon Resonances Shigeyuki Tajima The Jefferson Lab (JLab) E01-006 collaboration performed precise measurement of the spin structure functions of the proton and deuteron in the region of nucleon resonances (final state invariant mass $W<2$) at the four-momentum transfer squared of $Q^2\sim1.3$(GeV/c)$^2$. The W dependence of A$_1$ and A$_2$ has been measured with high resolution, allowing for clear identification of individual resonance regions. The spin structure measurements in the resonance region allow us to study the local duality for the polarized spin structure functions. In this experiment, the longitudinally-polarized electron beam of 5.755 GeV energy was scattered from a polarized solid ammonia target in Hall C at JLab. The scattered electrons were then detected in High Momentum Spectrometer (HMS), which allows us to measure inclusive scattering asymmetries. Ordinary (NH$_3$) and deuterated (ND$_3$) ammonia were used as polarized proton and deuteron targets. High precision measurements of the beam-target asymmetries ($A_\parallel$ and $A_\perp$) with polarization of the target material being parallel or perpendicular to the beam direction allow us to determine the spin asymmetries ($A_1(W, Q^2)$ and $A_2(W, Q^2)$) and the spin structure functions ($g_1(x, Q^2)$ and $g_2(x, Q^2)$) in a model independent way. In this talk, preliminary results for the deuteron spin asymmetries and structure functions as well as very preliminary results for the neutron will be presented. [Preview Abstract] |
Wednesday, September 21, 2005 11:45AM - 12:00PM |
EG.00012: Coherent vector meson electroproduction off the deuteron Atilla Gonenc, Brian Raue, Laird Kramer QCD predicts Color Transparency (CT), which refers to nuclear medium becoming transparent to a small color neutral object produced in high momentum transfer reactions, due to reduced strong interaction. Despite several studies at BNL, SLAC, FNAL, DESY and Jefferson Lab, a definitive signal for CT still remains elusive. In this paper, we present the results of a new study at Jefferson Lab motivated by theoretical calculations that suggest fully exclusive measurement of coherent vector meson electroproduction off the deuteron is a favorable channel for studying CT. Vector meson production has a large cross section at high energies, and the deuteron is the best understood and simplest nuclear system. Exclusivity allows the production and propagation to be controlled separately by controlling $Q^2$, $l_f$ (formation length), $l_c$ (coherence length) and $t$. This control is important as the rapid expansion of small objects increases their interaction probability and masks CT. The CT signal appears in a ratio of cross sections at high $-t$ (where rescattering is significant) to low $-t$ (where single nucleon reactions dominate). [Preview Abstract] |
Wednesday, September 21, 2005 12:00PM - 12:15PM |
EG.00013: Precise Measurement of the Nuclear Dependence of Structure Functions in Light Nuclei Jason Seely The EMC effect has been with us for over 20 years. During this time, the nuclear dependence of the structure functions, and thus quark distributions, has been studied with much success. However, the bulk of the experimental effort has been to measure the effect in heavy nuclei where it has the same $x$ dependence and differs only in magnitude. Calculations predict large differences in both the magnitude and $x$-dependence of the EMC effect in $^{3}$He and $^{4}$He and precise measurements of the EMC effect in these nuclei could be used to distinguish between existing models. To that end, E03-103 has measured the inclusive electron scattering cross-section on $^{1}$H, $^{2}$H, $^{3}$He, and $^{4}$He, as well as the heavier targets Be, C, Cu, and Au. These data will provide the first measurement of the EMC effect on $^{3}$He above $x>0.5$, and improve upon the existing measurement of the effect on $^{4}$He. Preliminary results for the EMC ratios on $^{3}$He and $^{4}$He will be presented. [Preview Abstract] |
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