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The E2/M1 ratio in {Delta} photoproduction

Description: The properties of the transition from the nucleon to the {Delta}(1232) serve as a benchmark for models of nucleon structure. To first order, N {r_arrow} {Delta} photo-excitation is dominated by a simple M1 quark spin-flip transition. At higher order, small L = 2 components in the N and {Delta} wavefunctions allow this excitation to proceed via an electric quadrupole transition. Since Nucleon models differ greatly on the mechanisms used to generate these L = 2 components,, the ratio of E2/M1 transitions (EMR) provides a sensitive test for structure models. Here, new high-precision measurements of p({rvec {gamma}}, {pi}) and p({rvec {gamma}}, {gamma}) cross sections and beam asymmetries have been combined with other polarization ratios in a simultaneous analysis of both reactions. Compton scattering has provided two important new constraints on the photo-pion amplitude. The E2/M1 mixing ratio for the N {r_arrow} {Delta} transition extracted from this analysis is EMR = {minus}3.0% {+-} 0.3 (stat+sys) {+-} 0.2 (model).
Date: August 1, 1997
Creator: Sandorfi, A.M.; Blanpied, G.; Blecher, M. & Collaboration, LEGS
Partner: UNT Libraries Government Documents Department

The E2/M1 ratio in {Delta} photoproduction

Description: New high-precision measurements of p({rvec {gamma}}, {pi}) and p({rvec {gamma}}, {gamma}) cross sections and beam asymmetries have been combined with other polarization ratios in a simultaneous analysis of both reactions. The E2/M1 mixing ratio for the n {r_arrow} {Delta} transition extracted from this analysis is EMR = {minus}3.0% {+-} 0.3 (stat+sys) {+-} 0.2 (model).
Date: October 1, 1997
Creator: Hoblit, S.; Blanpied, G.; Blecher, M. & Collaboration, LEGS
Partner: UNT Libraries Government Documents Department

Photon scattering from the nucleon at LEGS (Laser Electron Gamma Source)

Description: The elastic scattering of linearly polarized photons is discussed as a means of measuring the E2/M1 mixing ratio in the excitation of the delta (1232) resonance. The crucial problem in extracting this quantity is the presence of interfering backgrounds. The difference of two scattering cross sections with different incident polarizations can be used to eliminate almost all of the background contributions. As a measure of the sensitivity of this method, such a cross section difference can exhibit a change of 2.4% for an E2/M1 ratio of one percent. The single correction of importance comes from the imaginary part of the fmm(1-) amplitude for magnetic dipole scattering through a spin 1/2 state. It is likely that this amplitude is strongly affected by the tail of the P11 (1470) Roper resonance, and new multipole analyses of photoproduction and Compton scattering, extending up to the energy of the P11, would help to control the errors on this term. 20 refs., 5 figs., 3 tabs.
Date: January 1, 1988
Creator: Sandorfi, A.M.; Blanpied, G.; Blecher, M.; Giordano, G.; Kistner, O.C.; Matone, G. et al.
Partner: UNT Libraries Government Documents Department

Scattering of polarized photons at LEGS

Description: The Laser-Electron-Gamma-Source (LEGS) facility at Brookhaven National Laboratory is now coming into operation. This facility delivers intense, monochromatic beams of medium-energy gamma rays that are almost completely polarized (linear or circular), and this degree of freedom has altered the status of a number of important experiments from being impossible to now being merely difficult. In this lecture we will describe the key features of the LEGS facility, and discuss two elastic scattering experiments on the nucleon, one in the region of the first resonance which is sensitive to the E2/M1 mixing ratio in the delta, and the other below pion threshold which is sensitive to the nucleon polarizabilities. These will illustrate the unique potential of the polarization degree of freedom. 36 refs., 9 figs., 4 tabs.
Date: January 1, 1988
Creator: Sandorfi, A.M.; Blanpied, G.; Blecher, M.; Giordano, G.; Kistner, O.C.; Matone, G. et al.
Partner: UNT Libraries Government Documents Department

A portable cryostat for the cold transfer of polarized solid HD targets: HDice-I

Description: A device has been developed with moveable liquid nitrogen and liquid helium volumes that is capable of reaching over two meters into the coldest regions of a cryostat or dilution refrigerator and reliably extracting or installing a target of solid, polarized hydrogen deuteride (HD). This Transfer Cryostat incorporates a cylindrical neodymium rare-earth magnet that is configured as a Halbach dipole, which is maintained at 77 K and produces a 0.1 T field around the HD target. Multiple layers provide a hermetic 77 K-shield as the device is used to maintain a target at 2 K during a transfer between cryostats. Tests with frozen-spin HD show negligible polarization loss for either H or D over typical transfer periods. Multiple target transfers with this apparatus have shown an overall reliability of about 95% per transfer, which is a significant improvement over earlier versions of the device.
Date: February 1, 2014
Creator: Bass, Christopher D.; Sandorfi, Andy M.; Bade, C.; Blecher, M.; Caracappa, A.; D'Angelo, A. et al.
Partner: UNT Libraries Government Documents Department