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Theoretical study of the radiative capture reactions {sup 2}H(n,{gamma}){sup 3}H and {sup 2}H(p,{gamma}){sup 3}He at low energies

Description: Correlated Hyperspherical Harmonics wave functions with {Delta}-isobar admixtures obtained from realistic interactions are used to study the thermal neutron radiative capture on deuterium, and the {sup 2}H({rvec p},{gamma}){sup 3}He and p({rvec d},{gamma}){sup 3}He reactions in the center of mass energy range 0-100 keV. The nuclear electromagnetic current includes one and two-body components. Results for the {sup 2}H({rvec d},{gamma}){sup 3}H cross section and photon polarization parameter, as well as for the energy dependence of the astrophysical factor and angular distributions of the differential cross section, vector and tensor analyzing powers, and photon linear polarization coefficient of the {sup 2}H({rvec p},{gamma}){sup 3}He and p({rvec d},{gamma}){sup 3}He reactions are reported. Large effects due to two-body currents, in particular the long-range ones associated with the tensor component of the nucleon-nucleon interaction, are observed in the photon polarization parameter and vector analyzing power. Good, quantitative agreement between theory and experiment is found for all observables, with the exception of the vector analyzing power for which the calculated values underestimate the data by about 30%.
Date: February 1, 1996
Creator: Viviani, M.; Schiavilla, R. & Kievsky, A.
Partner: UNT Libraries Government Documents Department

Calculation of the {alpha}-particle ground state

Description: The Correlated Hyperspherical Harmonic expansion method is used to calculate alpha-particle properties with a realistic hamiltonian consisting of the Argonne V14 two nucleon and Urbana model VIII three nucleon potentials. The calculated binding energy, mass radius and wave percentages are close to the corresponding quantities obtained with Green's Function Monte Carlo and Faddeev-Yakubovsky techniques.
Date: October 1, 1994
Creator: Viviani, M.; Kievsky, A. & Rosati, S.
Partner: UNT Libraries Government Documents Department

Three-Nucleon Electroweak Capture Reactions

Description: Recent advances in the study of the p-d radiative and mu-3he weak capture processes are presented and discussed. The three-nucleon bound and scattering states are obtained using the correlated-hyperspherical-harmonics method, with realistic Hamiltonians consisting of the Argonne v14 or Argonne v18 two-nucleon and Tucson-Melbourne or Urbana IX three-nucleon interactions. The electromagnetic and weak transition operators include one- and two-body contributions. The theoretical accuracy achieved in these calculations allows for interesting comparisons with experimental data.
Date: October 1, 2002
Creator: Marcucci, L.E.; Viviani, M.; Kievsky, A.; Rosati, S. & Schiavilla, R.
Partner: UNT Libraries Government Documents Department

Electromagnetic and Weak transitions in light nuclei

Description: Recent advances in the study of the p -- d radiative and mu -- {sup 3}He weak capture processes by our group are presented and discussed. The trinucleon bound and scattering states have been obtained from variational calculations by expanding the corresponding wave functions in terms of correlated hyper-spherical harmonic functions. The electromagnetic and weak transition currents include one- and two-body operators. The accuracy achieved in these calculations allows for interesting comparisons with experimental data.
Date: September 1, 2002
Creator: Viviani, M.; Marcucci, L.E.; Kievsky, A.; Rosati, S. & Schiavilla, R.
Partner: UNT Libraries Government Documents Department

Realistic calculation of the hep astrophysical factor

Description: The astrophysical factor for the proton weak capture on {sup 3}He is calculated with correlated-hyperspherical-harmonics bound and continuum wave functions corresponding to a realistic Hamiltonian consisting of the Argonne {nu}{sub 18} two-nucleon and Urbana-IX three-nucleon interactions. The nuclear weak charge and current operators have vector and axial-vector components, that include one- and many-body terms. All possible multipole transitions connecting any of the p{sup 3}He S- and P-wave channels to the {sup 4}He bound state are considered. The S-factor at a p{sup 3}He center-of-mass energy of 10 keV, close to the Gamow-peak energy, is predicted to be 10.1 x 10{sup {minus}20} keV b, a factor of five larger than the standard-solar-model value. The P-wave transitions are found to be important, contributing about 40 % of the calculated S-factor.
Date: March 1, 2000
Creator: Marcucci, L.E.; Schiavilla, R.; Viviani, M.; Kievsky, A. & Rosati, S.
Partner: UNT Libraries Government Documents Department

Photo- and electro-disintegration of {sup 3}He at threshold and pd radiative capture

Description: The present work reports results for: (1) pd radiative capture observables measured at center-of-mass (c.m.) energies in the range 0--100 keV and at 2 MeV by the TUNL and Wisconsin groups, respectively; (2) contributions to the Gerasimov-Drell-Hearn (GDH) integral in {sup 3}He from the two- up to the three-body breakup thresholds, compared to experimental determinations by the TUNL group in this threshold region; (3) longitudinal, transverse, and interference response functions measured in inclusive polarized electron scattering off polarized {sup 3}He at excitation energies below the threshold for breakup into ppn, compared to unpolarized longitudinal and transverse data from the Saskatoon group. The calculations are based on pair-correlated-hyperspherical-harmonics bound and continuum wave functions obtained from a realistic Hamiltonian consisting of the Argonne {upsilon}{sub 18} two-nucleon and Urbana IX three-nucleon interactions. The electromagnetic current operator includes one- and two- body components, leading terms of which are constructed from the Argonne {upsilon}{sub 18} interaction (specifically, its charge-independent part). Two-body currents associated with {Delta}-isobar degrees of freedom are treated non-perturbatively via the transition-correlation-operator method. The theoretical predictions obtained by including only one-body currents are in violent disagreement with data. These differences between theory and experiment are, to a large extent, removed when two-body currents are taken into account, although some rather large discrepancies remain in the c.m. energy range 0--100 keV, particularly for the pd differential cross section {sigma}({theta}) and tensor analyzing power T{sub 20}({theta}) at small angles, and contributions to the GDH integral. A rather detailed analysis indicated that these discrepancies have, in large part, a common origin, and can be traced back to an excess strength obtained in the theoretical calculation of the E{sub 1} reduced matrix element associated with the pd channel having L,S,J = 1, 1/2, 3/2. It is suggested that this lack of E{sub 1} strength observed experimentally might ...
Date: November 1, 1999
Creator: Viviani, M.; Kievsky, A.; Marcucci, L.E.; Rosati, S. & Schiavilla, R.
Partner: UNT Libraries Government Documents Department

Theoretical Study of the {sup 3}He({mu}, {nu}{sub {mu}}){sup 3}H Capture

Description: The {sup 3}He({mu}, {nu}{sub {mu}}){sup 3}H weak capture is studied using correlated-hyperspherical-harmonics wave functions, obtained from realistic Hamiltonians consisting of the Argonne v{sub 14} or Argonne v{sub 18} two-nucleon, and Tucson-Melbourne or Urbana-IX three-nucleon interactions. The nuclear weak charge and current operators have vector and axial-vector components that include one- and two-body contributions. The strength of the leading two-body operator in the axial-vector current is adjusted to reproduce the Gamow-Teller matrix element in tritium {beta}-decay. The calculated total capture rate is in excellent agreement with the most recent experimental determination 1496 {+-} 4 sec{sup -1}, when the PCAC value is adopted for the induced pseudo-scalar coupling constant g{sub PS}. The predictions for the capture rate and angular correlation parameters A{sub v}, A{sub t}, and A{sub {Delta}} are found to be only very weakly dependent on the model input Hamiltonian. The variation of these observables with g{sub PS} and the theoretical uncertainties deriving from the model-dependent procedure used to constrain the axial current are investigated.
Date: December 1, 2001
Creator: Marcucci, L.E.; Schiavilla, R.; Rosati, S.; Kievsky, A. & Viviani, M.
Partner: UNT Libraries Government Documents Department

Weak proton capture on {sup 3}He

Description: The astrophysical S-factor for the proton weak capture on {sup 3}He is calculated with correlated-hyperspherical-harmonics bound and continuum wave functions corresponding to realistic Hamiltonians consisting of the Argonne {upsilon}{sub 14} or Argonne {upsilon}{sub 18} two-nucleon and Urbana-VIII or Urbana-IX three-nucleon interactions. The nuclear weak charge and current operators have vector and axial-vector components, that include one- and many-body terms. All possible multipole transitions connecting any of the p {sup 3}He S- and P-wave channels to the {sup 4}He bound state are considered. The S-factor at a p {sup 3}He center-of-mass energy of 10 keV, close to the Gamow-peak energy, is predicted to be 10.1 x 10{sup {minus}20} keV b with the AV18/UIX Hamiltonian, a factor of about 4.5 larger than the value adopted in the standard solar model. The P-wave transitions are found to be important, contributing about 40% of the calculated S-factor. The energy dependence is rather weak: the AV18/UIX zero-energy S-factor is 9.64 x 10{sup {minus}20} keV b, only 5% smaller than the 10 keV result quoted above. The model dependence is also found to be weak: the zero-energy S-factor is calculated to be 10.2 x 10{sup {minus}20} keV b with the older AV14/UVIII model, only 6% larger than the AV18/UIX result. Their best estimate for the S-factor at 10 keV is therefore (10.1 {+-} 0.6) x 10{sup {minus}20} keV b, when the theoretical uncertainty due to the model dependence is included. This value for the calculated S-factor is not as large as determined in fits to the Super-Kamiokande data in which the hep flux normalization is free. However, the precise calculation of the S-factor and the consequent absolute prediction for the hep neutrino flux will allow much greater discrimination among proposed solar neutrino oscillation solutions.
Date: March 1, 2000
Creator: Marcucci, L.E.; Schiavilla, R.; Viviani, M.; Kievsky, A.; Rosati, S. & Beacom, J.F.
Partner: UNT Libraries Government Documents Department

Parameter-Free Calculation of the Solar Proton Fusion Rate in Effective Field Theory

Description: Spurred by the recent complete determination of the weak currents in two-nucleon systems up to O(Q{sup 3}) in heavy-baryon chiral perturbation theory, we carry out a parameter-free calculation of the solar proton fusion rate in an effective field theory that combines the merits of the standard nuclear physics method and systematic chiral expansion. Using the tritium {beta}-decay rate as an input to fix the only unknown parameter in the effective Lagrangian, we can evaluate with drastically improved precision the ratio of the two-body contribution to the well established one-body contribution; the ratio is determined to be (0.9 {+-} 0.1)%. This result is essentially independent of the cutoff parameter for a wide range of its variation (500 MeV {le} {Lambda} {+-} 800 MeV), a feature that substantiates the consistency of the calculation.
Date: June 1, 2001
Creator: Park, T.-S.; Marcucci, L.E.; Schiavilla, R.; Viviani, M.; Kievsky, A.; Rosati, S. et al.
Partner: UNT Libraries Government Documents Department

The Solar hep Process in Effective Field Theory

Description: Using effective field theory, we calculate the S-factor for the hep process in a totally parameter-free formulation. The transition operators are organized according to chiral counting, and their matrix elements are evaluated using the realistic nuclear wave functions obtained in the Correlated-hyperspherical-harmonics method. Terms of up to next-to-next-to-next-to-leading order in heavy-baryon chiral perturbation theory are considered. Fixing the only parameter in the theory by fitting the tritium beta-decay rate, we predict the hep S-factor with accuracy better than {approx} 20%.
Date: September 1, 2001
Creator: Park, T.-S.; Marcucci, L. E.; Schiavilla, R.; Viviani, M.; Kievsky, A.; Rosati, S. et al.
Partner: UNT Libraries Government Documents Department

Parameter-free effective field theory calculation for the solar proton-fusion and hep processes

Description: Spurred by the recent complete determination of the weak currents in two-nucleon systems up to {Omicron}(Q{sup 3}) in heavy-baryon chiral perturbation theory, we carry out a parameter-free calculation of the threshold S-factors for the solar pp (proton-fusion) and hep processes in an effective field theory that combines the merits of the standard nuclear physics method and systematic chiral expansion. The power of the EFT adopted here is that one can correlate in a unified formalism the weak-current matrix elements of two-, three- and four-nucleon systems. Using the tritium {beta}-decay rate as an input to fix the only unknown parameter in the theory, we can evaluate the threshold S factors with drastically improved precision; the results are S{sub pp}(0) = 3.94 x (1 {+-} 0.004) x 10{sup -25} MeV-b and S{sub hep}(0) = (8.6 {+-} 1.3) x 10{sup -20} keV-b. The dependence of the calculated S-factors on the momentum cutoff parameter {Lambda} has been examined for a physically reasonable range of {Lambda}. This dependence is found to be extremely small for the pp process, and to be within acceptable levels for the hep process, substantiating the consistency of our calculational scheme.
Date: August 1, 2002
Creator: Park, T.S.; Marcucci, L.E.; Schiavilla, R.; Viviani, M.; Kievsky, A.; Rosati, S. et al.
Partner: UNT Libraries Government Documents Department