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- All Subjects: Nuclear Physics
- Creators: Dugger, Michael
- Creators: Beckstein, Oliver
Description
The nucleon resonance spectrum consists of many overlapping excitations. Polarization observables are an important tool for understanding and clarifying these spectra. While there is a large data base of differential cross sections for the process, very few data exist for polarization observables. A program of double polarization experiments has been conducted at Jefferson Lab using a tagged polarized photon beam and a frozen spin polarized target (FROST). The results presented here were taken during the first running period of FROST using the CLAS detector at Jefferson Lab with photon energies ranging from 329 MeV to 2.35 GeV. Data are presented for the E polarization observable for eta meson photoproduction on the proton from threshold (W=1500 MeV) to W=1900 MeV. Comparisons to the partial wave analyses of SAID and Bonn-Gatchina along with the isobar analysis of eta-MAID are made. These results will help distinguish between current theoretical predictions and refine future theories.
ContributorsMorrison, Brian (Author) / Ritchie, Barry (Thesis advisor) / Dugger, Michael (Committee member) / Shovkovy, Igor (Committee member) / Davies, Paul (Committee member) / Alarcon, Ricardo (Committee member) / Arizona State University (Publisher)
Created2011
Description
A search is underway to find baryon resonances that have been predicted, but yet remain unobserved. Nucleon resonances, due to their broad energy widths, overlap and must be disentangled in order to be identified. Meson photoproduction observables related to the orientation of the spin of the incoming photon and the spin of the target proton are useful tools to deconvolve the nucleon resonance spectrum. These observables are particularly sensitive to interference between phases of the complex amplitudes. A set of these observables has been measured using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab with linearly-polarized photons having energies from 725 to 1575 MeV with polar angle values of cos(theta) between -0.8 and 0.9 and transversely-polarized protons in the Jefferson Lab FRozen Spin Target (FROST). By fitting neutron yields from gamma p -> pi^+ n over azimuthal scattering angle, the observables \H and P have been extracted. These observables manifest as azimuthal modulations in the yields for the double-polarization experiment. Preliminary results for these observables will be presented and compared with predictions provided by the SAID Partial-Wave Analysis Facility.
ContributorsLee, Robert John (Author) / Dugger, Michael (Thesis director) / Ritchie, Barry (Committee member) / Department of Physics (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
In nuclear physics, there is a discrepancy between theory and experiment concerning the number of existing nucleon resonances. Current models predict far more states than have been observed. In particular, few searches have found excited nucleon resonances with energies above 2.2 GeV in the K Lambda channel. To investigate high-mass nucleon resonances, efficiency-corrected yields of the reaction ep --> e K+ Lambda(1520) --> e K+ K- p in the center-of-mass energy range 2.1-4.5 GeV are constructed utilizing Jefferson Lab's CLAS12 detector. This paper presents the results of an analysis searching for high-mass nucleon resonances in the K Lambda channel between 2.1-4.5 GeV.
ContributorsOsar, Rebecca (Author) / Dugger, Michael (Thesis director) / Ritchie, Barry (Committee member) / Barrett, The Honors College (Contributor) / Department of Physics (Contributor) / School of International Letters and Cultures (Contributor)
Created2023-05
Description
Quantum Monte Carlo is one of the most accurate ab initio methods used to study nuclear physics. The accuracy and efficiency depend heavily on the trial wave function, especially in Auxiliary Field Diffusion Monte Carlo (AFDMC), where a simplified wave function is often used to allow calculations of larger systems. The simple wave functions used with AFDMC contain short range correlations that come from an expansion of the full correlations truncated to linear order. I have extended that expansion to quadratic order in the pair correlations. I have investigated this expansion by keeping the full set of quadratic correlations as well an expansion that keeps only independent pair quadratic correlations. To test these new wave functions I have calculated ground state energies of 4He, 16O, 40Ca and symmetric nuclear matter at saturation density ρ = 0.16 fm−3 with 28 particles in a periodic box. The ground state energies calculated with both wave functions decrease with respect to the simpler wave function with linear correlations only for all systems except 4He for both variational and AFDMC calculations. It was not expected that the ground state energy of 4He would decrease due to the simplicity of the alpha particle wave function. These correlations have also been applied to study alpha particle formation in neutron rich matter, with applications to neutron star crusts and neutron rich nuclei. I have been able to show that this method can be used to study small clusters as well as the effect of external nucleons on these clusters.
ContributorsPetrie, Cody L (Author) / Schmidt, Kevin E (Thesis advisor) / Shovkovy, Igor A. (Committee member) / Beckstein, Oliver (Committee member) / Alarcon, Ricardo O (Committee member) / Arizona State University (Publisher)
Created2019
Description
A series of experiments using a polarized beam incident on a polarized frozen spin target
(FROST) was conducted at Jefferson Lab in 2010. Results presented here were taken
during the second running period with the FROST target using the CEBAF Large Acceptance
Spectrometer (CLAS) detector at Jefferson Lab, which used transversely-polarized
protons in a butanol target and a circularly-polarized incident tagged photon beam with
energies between 0.62 and 2.93 GeV. Data are presented for the F and T polarization observables
for h meson photoproduction on the proton from W = 1.55 GeV to 1.80 GeV.
The data presented here will improve the world database and refine theoretical approaches
of nucleon structure.
(FROST) was conducted at Jefferson Lab in 2010. Results presented here were taken
during the second running period with the FROST target using the CEBAF Large Acceptance
Spectrometer (CLAS) detector at Jefferson Lab, which used transversely-polarized
protons in a butanol target and a circularly-polarized incident tagged photon beam with
energies between 0.62 and 2.93 GeV. Data are presented for the F and T polarization observables
for h meson photoproduction on the proton from W = 1.55 GeV to 1.80 GeV.
The data presented here will improve the world database and refine theoretical approaches
of nucleon structure.
ContributorsTucker, Ross (Author) / Ritchie, Barry (Thesis advisor) / Dugger, Michael (Committee member) / Alarcon, Ricardo (Committee member) / Lebed, Richard (Committee member) / Arizona State University (Publisher)
Created2016