Bulletin of the American Physical Society
2005 APS April Meeting
Saturday–Tuesday, April 16–19, 2005; Tampa, FL
Session J2: New Results on the Structure of the Nucleon and Nucleus |
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Sponsoring Units: DNP Chair: Haiyan Gao, Duke University Room: Marriott Tampa Waterside Grand Salon F |
Sunday, April 17, 2005 10:45AM - 11:21AM |
J2.00001: Lattice Calculations of Nucleon Form Factors Invited Speaker: Modern calculations of the electromagnetic structure in lattice QCD are reviewed. Two principal limitations of these calculations are the use of unphysically large quark masses and the quenched approximation --- where the effects of dynamical sea quarks are neglected. Both of these issues are considered in chiral effective field theory formulated with a finite-range regulator. A simple phenomenological study highlights that lattice QCD can describes the qualitative behaviour of the form factors over a range of momentum transfer, up to $Q^2\sim 1.0$ GeV$^2$. A much more sophisticated analysis of the moment alone, with high statistics lattice results, enables the extraction of the entire octet baryon magnetic moments. These results, combined with charge symmetry, provide a precise prediction of the strangeness contribution to the proton's magnetic moment. [Preview Abstract] |
Sunday, April 17, 2005 11:21AM - 11:57AM |
J2.00002: Spin-Dependent Electron Scattering from Deuterium at BLAST Invited Speaker: The BLAST experiment, at the MIT-Bates Linear Accelerator Laboratory, was designed to study in a systematic manner the spin-dependent, electro-magnetic interaction in few-nucleon systems at momentum transfers below 1~GeV/c. In 2004 BLAST collected approximately 170 pb$^{-1}$ of data with polarized electrons scattering from polarized deuterium at a beam energy of 850~MeV. The beam polarization was typically 65\%. An internal gas target of isotopically pure, polarized deuterium was produced by an atomic beam source. Typical polarizations of around 75\% for vector and 70\% for tensor were achieved. The BLAST detector is a large acceptance general purpose detector based on a toroidal magnetic field with an approximate left-right symmetry. The trigger and data acquisition system allows simultaneous measurements of several reaction channels. Reversing the beam helicity each fill and frequent changing of the target polarization during each fill minimizes systematic errors and allows measurements to be made of both beam and target asymmetries for kinematics approximately parallel and perpendicular to the target polarization. The data are being analyzed for elastic $eD$ scattering as well as quasi-elastic ($e^\prime p$ and $e^\prime n$) and inclusive channels. Preliminary results will be presented from each of these analyses. These results will include new information on the deuteron form factors as well as the extracted neutron form factors $G_E^n$ and $G_M^n$. These results will be compared with existing data and current theoretical calculations. [Preview Abstract] |
Sunday, April 17, 2005 11:57AM - 12:33PM |
J2.00003: Casting Light on Neutron Halo Nuclei Invited Speaker: Laser spectroscopic measurements of atomic isotope shifts provide unique access to the nuclear charge distribution of short-lived isotopes. In this talk, I will present a new high-resolution technique based on laser spectroscopy of single atoms cooled and confined in a magneto-optical trap. The isotopes of interest are $^6$He (t$_{1/2}$ = 807 ms) and $^8$He (t$_{1/2}$ = 119 ms), which exhibit a loosely bound neutron halo around a $^4$He-like core. I will report on our recent high-precision measurement of the $^6$He nuclear charge radius and the progress in extending this investigation to $^8$He. Charge radii measurements of both isotopes provide corroboration for their halo structure and test theoretical models of light nuclei. [Preview Abstract] |
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