Bulletin of the American Physical Society
2010 Fall Meeting of the APS Division of Nuclear Physics
Volume 55, Number 14
Tuesday–Saturday, November 2–6, 2010; Santa Fe, New Mexico
Session DF: Theoretical Methods |
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Chair: Richard Silbar, Los Alamos National Laboratory Room: Kearney |
Thursday, November 4, 2010 10:30AM - 10:42AM |
DF.00001: A Regge Model for Nucleon-Nucleon Scattering Amplitudes William Ford, J. Wallace Van Orden We present a model to calculate nucleon-nucleon (NN) scattering amplitudes, at laboratory kinetic energies greater than 1.3 GeV. The model, based on Regge theory, is fully relativistic, and exhibits full spin dependence. We relate the Regge exchanges to the Fermi invariants, which gives an organized and simplified method to incorporate Regge exchanges into the NN scattering. An added benefit is that all spin dependence is explicitly dealt with. The parameters in the model are from the Regge trajectories, which are obtained from the meson spectrum, and the residues. We employ phenomenological residues, which we determine by fitting our model to total and differential cross section data, and the SAID helicity amplitudes. Preliminary results are presented. [Preview Abstract] |
Thursday, November 4, 2010 10:42AM - 10:54AM |
DF.00002: Effective Field Theory for Light Nuclear Systems Jimmy Rotureau, Ionel Stetcu, Bruce Barrett, Ubirajara Van Kolck We have applied the general principles of Effective Field Theory for the description of light nuclear systems. The interactions between nucleons is written as a controllable expansion consisting of contact interactions with an increasing number of derivatives. The many-body dynamics is solved with the No-Core Shell model approach. The nucleons are assumed to evolve in a harmonic oscillator trap characterized by the frequency $\omega$. The presence of the trap allows for the construction of nuclear interactions within the shell-model valence space directly from the low-energy scattering physics given by the effective range expansion. Binding and excitation energies of nuclear systems in the absence of a trap are obtained by taking the limit $\omega \rightarrow 0$. Results for $^3H$ and $^4He$ at leading order and next-to-leading order will be discussed. [Preview Abstract] |
Thursday, November 4, 2010 10:54AM - 11:06AM |
DF.00003: Nuclear Electromagnetic Currents in Chiral Effective Field Theory Saori Pastore We have derived nuclear electromagnetic currents in chiral effective field theory with pions and nucleons as explicit degrees of freedom. The calculation has been carried out in time-ordered perturbation theory up to include N$^3$LO corrections, consisting of two--pion exchange, and contact contributions. Here I will present our calculation and discuss the results obtained for a number of electromagnetic observables of $A\leq4$ nuclei. [Preview Abstract] |
Thursday, November 4, 2010 11:06AM - 11:18AM |
DF.00004: Electroweak Pion and Photon Production from Nuclei in a Chiral Effective Field Theory Brian D. Serot, Xilin Zhang The electroweak response of the nuclear many-body system is investigated at intermediate energies, where the $\Delta$ resonance becomes important. The theory is applied to pion and photon production from nuclei, which are potential backgrounds in the MiniBooNE experiment. The Lorentz-invariant effective field theory contains nucleons, pions, Deltas, isoscalar scalar $(\sigma )$ and vector $(\omega )$ fields, and isovector vector $(\rho )$ fields. The lagrangian exhibits a nonlinear realization of $SU(2)_L \times SU(2)_R$ chiral symmetry and incorporates vector-meson dominance. Power counting for vertices and diagrams involving the $\Delta$ is discussed. To calibrate the axial vector current, pion production from the nucleon is used as a benchmark. For calculations with nuclei, we use a local, relativistic Fermi gas description based on the relativistic mean-field theory ground state. Quasielastic electron scattering and pion electroproduction are used to test the nuclear model and to determine the $\Delta$ interactions in the nuclear medium. Final state interactions are ignored. Results for neutrino-induced pion and photon production on ${}^{12}$C, ${}^{16}$O, and ${}^ {56}$Fe are shown. The relationship to the excess events seen at low energies at MiniBooNE is discussed. [Preview Abstract] |
Thursday, November 4, 2010 11:18AM - 11:30AM |
DF.00005: Parallel algorithms and applications of configuration-interaction shell-model code BIGSTICK Plamen Krastev, Calvin Johnson, Erich Ormand Nuclear shell-model, together with two- and three-body interactions, is a powerful tool for gaining insight for properties of light nuclei. The aid of advanced computer resources is of major importance in such calculations. We report on the latest developments and applications of configuration-interaction shell-model code BIGSTICK -- an efficient parallel on-the-fly code which solves the nuclear many-body problem with both two- and three-body interactions. The US Department of Energy supported this investigation through Contract Nos. DE-FG02-96ER40985 and DE-FC02- 09ER41587 and through Subcontract No. B576152 of the Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344. [Preview Abstract] |
Thursday, November 4, 2010 11:30AM - 11:42AM |
DF.00006: Ratio of Isoscalar to Isovector Core Polarization Contributions to Magnetic Moments Shadow Robinson, Larry Zamick, Yitzhak Sharon We found that large scale calculations of isoscalar magnetic moments of odd-odd N=Z nuclei yielded results remarkably similar to those of simple single j calculations. To understand why we use a delta interaction times (1+xPs) where Ps is the spin exchange operator, to calculate the ratio IS/IV of the core polarization contributions to the magnetic moments. The spin exchange contributes a factor (1-2x) to this ratio. A popular choice is x=1/3 for which (1-2x) is also 1/3. Another contribution comes from the fact that the coupling of j=l+1/2 to j'=l-1/2 via the magnetic moment operator is proportional to (gs-gl). The IS values are gl=0.5 gs=0.88; the IV values are 0.5 and 4.71. This yields a (gs-gl) ratio of 0.09 which together with the 1/3 from spin exchange tells us that the isoscalar core polarization is a mere 3\% of isovector. If we further divide by single j values to get effective charge corrections then the ration IS/IV ends up being 0.06 (or 6\%). We thus gain understanding of the resuts in ref [1] of the near equality of large scale and single j results for IS moments.\\[4pt] [1] S.Yeager, S.J.Q. Robinson, L.Zamick and Y.Y.Sharon, EPL 88, 52001 (2009) [Preview Abstract] |
Thursday, November 4, 2010 11:42AM - 11:54AM |
DF.00007: Collective Motion in Soft Spherical Nuclei: Microscopic Description Liyuan Jia, Vladimir Zelevinsky The Generalized Density Matrix (GDM) method is used to microscopically calculate the parameters of the collective Hamiltonian for soft spherical nuclei. We map the equation of motion for the GDM onto the collective degrees of freedom. The lowest orders give the Hartree-Fock-Bogoliubov equations and the random phase approximation (RPA) equation naturally. For higher orders, the formalism was checked by the Lipkin model and the factorizable force model. We calculated the quartic anharmonicity that is responsible for restoring the stability of the system as the RPA frequency goes to zero. In both simple cases our approach agrees well with the known results. Applying the formalism to realistic nuclei, we calculate the collective Hamiltonian for quadrupole and octupole degrees of freedom including their interaction. This interplay is observed empirically and might be important in the search for enhancement of parity violation. The results are applied to collective excitations in medium soft nuclei. [Preview Abstract] |
Thursday, November 4, 2010 11:54AM - 12:06PM |
DF.00008: Systematics in the structure of low-lying, non-yrast configurations of strongly deformed nuclei Gabriela Popa Strongly deformed nuclei show interesting paterns in the energy spectrum above around 1 MeV. An empirical investigation of the trends in the properties of the energy levels of low angular momentum, in nuclei that are related to one another through the addition or removal of alpha-particle-like structures, reveals their complex and changing behavior in contrast to the smooth behavior of the yrast states. A systematic application of the pseudo-SU(3) model for such a sequence of deformed nuclei, from the rare earth region, leads to an accurate and unified description of not only yrast, but non-yrast collective bands. The onset of deformation as manifested through the position of the excited band-heads in the spectra is understood and interpreted by using a realistic model Hamiltonian in conjunction with a microscopic distribution of the eigenstates across allowed proton and neutron strong-coupled SU(3) configurations. [Preview Abstract] |
Thursday, November 4, 2010 12:06PM - 12:18PM |
DF.00009: Shell Model Interactions that Conserve Pseudospin Symmetry Joseph Ginocchio Nuclei approximately conserve pseudospin symmetry [1]. Normally shell model interactions are written in terms of spin an orbital angular momentum operators, not in terms of pseudospin and pseudo-orbital angular momentum operators. We determine the shell model interactions which conserve pseudospin symmetry and pseudo-orbital angular momentum symmetry and write them in terms of spin and orbital angular momentum operators including the tensor interaction. We show that, although the tensor interaction by itself does not conserve pseudo-orbital angular momentum, certain combinations of the tensor interaction with the two body spin orbit interaction do conserve pseudo-orbital angular momentum. \\[4pt] [1] J. N. Ginocchio, Physics Reports 414, 165 (2005). [Preview Abstract] |
Thursday, November 4, 2010 12:18PM - 12:30PM |
DF.00010: Transverse Charge Densities of Hadrons Gerald Miller Electromagnetic form factors have long been used to probe the underlying charge and magnetization densities of hadrons and nuclei. Traditional three-dimensional Fourier transform methods are not rigorously applicable for systems with constituents that move relativistically. The use of the transverse charge density is a new, rigorously defined way to analyze electromagnetic form factors of hadrons. This talk will be concerned with the meaning of transverse charge density and examples based on recent results. [Preview Abstract] |
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