Bulletin of the American Physical Society
APS April Meeting 2013
Volume 58, Number 4
Saturday–Tuesday, April 13–16, 2013; Denver, Colorado
Session C13: Structure & Reactions Involving Light Nuclei |
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Sponsoring Units: DNP Chair: June Matthews, Massachusetts Institute of Technology Room: Plaza Court 2 |
Saturday, April 13, 2013 1:30PM - 1:42PM |
C13.00001: Progress in Quantum Monte Carlo Calculations of Light Nuclei with Non-Local Potentials Joel Lynn, Kevin Schmidt, Joe Carlson, Stefano Gandolfi Monte Carlo methods often used in nuclear physics, such as auxiliary field diffusion Monte Carlo and Green's function Monte Carlo, have typically relied on phenomenological local real-space potentials containing as few derivatives as possible, such as the Argonne-Urbana family of interactions, to make sampling simple and efficient. Basis set methods such as no-core shell model or coupled-cluster techniques typically use softer non-local potentials because of their more rapid convergence with basis set size. These non-local potentials are typically defined in momentum space and are often based on effective field theory. Comparisons of the results of the two types of methods are complicated by the use of different potentials. I will discuss progress we have made in using such non-local potentials in quantum Monte Carlo calculations of light nuclei. In particular, I will show methods for evaluating the real-space, imaginary-time propagators needed to perform quantum Monte Carlo calculations using such non-local potentials, how to formulate a good trial wave function for such potentials, and how to perform a ``one-step'' Green's function Monte Carlo calculation for such potentials. [Preview Abstract] |
Saturday, April 13, 2013 1:42PM - 1:54PM |
C13.00002: Consistency in Quenching of ``Absolute'' Spectroscopic Factors from Transfer Reactions J.P. Schiffer, B.P. Kay, S.J. Freeman The strengths of single-particle transitions in $(e,e'p)$ knockout reactions on closed-shell nuclei are lower than expected,\footnote{G.~J.~Kramer {\it et al}., Nucl. Phys. {\bf A679}, 267 (2001).} due to limitations of the mean-field description imposed by correlations. This quenching of single-particle strength by $\sim$0.5 appeared to be a general property of nuclei from $^{16}$O to $^{208}$Pb. In our work, the combined sums of neutron-adding and neutron-removing strengths from $(d,p)$ and $(p,d)$ transfer reactions on four Ni isotopes yield very similar quenching factors of $\sim$0.53 (varying by $\sim$10\% with reasonable choices of optical-model parameters).\footnote{J.~P.~Schiffer {\it et al}., Phys. Rev. Lett. {\bf 108}, 022501 (2012).} Recently, spectroscopic overlaps between $^4$He and $^3$He were extracted from GFMC calculations.\footnote{I.~Brida {\it et al}., Phys. Rev. C {\bf 84}, 024319 (2011).} With these, our data on ($\alpha$,$^3$He) and ($^3$He,$\alpha$) on the Ni isotopes yields $\sim$0.62. Additional data for proton transfer on Ni and transfer on other nuclei are also being analyzed. This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357 and the U.K. Science and Technology Facilities Council. [Preview Abstract] |
Saturday, April 13, 2013 1:54PM - 2:06PM |
C13.00003: Microscopic Optical Potential for Scattering of $^6$He and $^8$He off Protons Charlotte Elster, Azamat Orazbayev, Stephen Weppner The calculation and derivation of microscopic optical potentials for obtaining scattering observables for elastic scattering from spin-zero nuclei has a long tradition. So-called microscopic ``folding'' models based on a nuclear density matrix and a fully-off-shell two-nucleon t-matrix have been developed mainly for closed shell, heavy nuclei. Constructing a microscopic optical potential for the Helium isotopes poses the challenge, that they are not closed-shell nuclei. In addressing this challenge, the Watson optical potential has been extended to incorporate the open-shell structure of $^6$He and $^8$He. This leads to additional contributions to the central and spin-orbit potential. Calculations based on an harmonic oscillator ansatz for the single-particle density matrix and the charge-dependent Bonn potential will be presented, and the effect of the additional terms on the differential cross section and the polarization will be discussed. [Preview Abstract] |
Saturday, April 13, 2013 2:06PM - 2:18PM |
C13.00004: Investigating halo features with the $^{11}$Be(p, d)$^{10}$Be transfer reaction at 110 MeV at TRIUMF-ISAC II K. Kuhn, R. Braid, F. Sarazin, D. Smalley, U. Hager, S. Ilyushkin, P. O'Malley, M.A.G. Alvarez, C. Andreoiu, P.C. Bender, G. Hackman, C. Unsworth, Z. Wang, W.N. Catford, C.Aa. Diget, A. DiPietro, P. Figuera, T.E. Drake, J. Gomez, E. Nacher, A. Perea, O. Tengblad, C.E. Svensson One-neutron transfer reactions are being used to study single-particle neutron states in nuclei. For one-neutron halo nuclei, such as $^{11}$Be, the (p,d) reaction enables the removal of the halo neutron or of one of the core neutrons. This way, it is possible to simultaneously study the halo wavefunction of the $^{11}$Be ground-state but also possible excited halo states in $^{10}$Be. The $^{11}$Be(p, d)$^{10}$Be transfer reaction at 10 MeV/nucleon is being investigated at the TRIUMF-ISAC II facility with a compact silicon array and the TRIUMF ISAC Gamma-Ray Escape-Suppressed Spectrometer (TIGRESS). The goal of this experiment is to study halo states in $^{11}$Be and $^{10}$Be created by the removal of a single neutron from $^{11}$Be. An initial experiment was carried out last summer and preliminary results will be presented. [Preview Abstract] |
Saturday, April 13, 2013 2:18PM - 2:30PM |
C13.00005: Direct Observation of a New $J^\pi = 2^+$ State in ${}^{12}\mathrm{C}$ through the ${}^{12}\mathrm{C}+\gamma \rightarrow 3\alpha$ Reaction W.R. Zimmerman, M.W. Ahmed, S.S. Henshaw, I. Mazumdar, J.M. Mueller, L.S. Myers, M.H. Sikora, S. Stave, H.R. Weller, M. Gai The second $J^\pi = 2^+$ state in ${}^{12}\mathrm{C}$, predicted over fifty years ago to exist as an excitation of the Hoyle state, has been unambiguously identified in the ${}^{12}\mathrm{C}$($\gamma$,$\alpha$)${}^{8}\mathrm{Be}$ reaction. The $\alpha$ particles produced by the photo\-disintegration of ${}^{12}\mathrm{C}$ were detected using an optical time projection chamber. Initial data were collected at beam energies between 9.1 and 10.7~MeV using intense, nearly mono\-energetic $\gamma$-ray beams available at the HI$\gamma$S facility. The measured cross sections and angular distributions unambiguously establish the existence of a broad $2^+$ state near 10~MeV in ${}^{12}\mathrm{C}$\@. Additional data were recently taken at beam energies of up to 11.2~MeV and show no evidence for an additional $2^+$ state previously reported to exist near 11 MeV [1]. \\[4pt] [1] F.~Ajzenberg-Selove, Nucl.\ Phys.\ {\bf A506}, 1 (1990). [Preview Abstract] |
Saturday, April 13, 2013 2:30PM - 2:42PM |
C13.00006: Determination of the ground state branching ratio in $^{14}$O$\rightarrow ^{14}$N beta decay Paul Voytas, Elizabeth George, Lynn Knutson, Gregory Severin The branching ratio of the $^{14}$O$\rightarrow^{14}$N beta decay is an important ingredient in analyses that use $0^+\rightarrow0^+$ superallowed beta decays to test the unitarity of the CKM matrix. In addition to the dominant $0^+\rightarrow0^+$ transition in this decay, there is a small $0^+\rightarrow1^+$ branch to the ground state. A reanalysis by Towner and Hardy of previous ground state branching ratio measurements shifted the recommended value of the ground state branching ratio by several error bars and also indicates that the two most precise previous measurements are not in good agreement with each other. The ground state branch is about 0.5\%\ and should be measured to a relative uncertainty of about 10\%\ to minimize the error contribution from this parameter. We will present new measurements of the beta spectra for the ground state and first excited state branches in $^{14}$O beta decay and discuss the implications for the ground state branching ratio. [Preview Abstract] |
Saturday, April 13, 2013 2:42PM - 2:54PM |
C13.00007: Universality and the matter radius of Carbon-22 Daniel Phillips, Bijaya Acharya, Chen Ji Recently, Tanaka et al. measured the matter radius of $^{22}$C to be $\langle {\rm r}_m^2 \rangle^{1/2}$=5.4 $\pm$ 0.9 fm. This suggests that ${}^{22}$C is an s-wave two-neutron halo, with the two neutrons orbiting a ${}^{20}$C core. We address this finding using an effective field theory (EFT) that employs core and neutron degrees of freedom and is designed for systems with a large two-body scattering length. This EFT enables the derivation of universal predictions for three-body systems which are built on such two-body interactions and have a large matter radius. We show that, at leading order in the EFT, the matter radius of any s-wave two-neutron halo is given by a function of the neutron-core scattering length and the halo nucleus' two-neutron separation energy. We display this function and discuss its general properties. Specializing to the case of ${}^{22}$C, we use our general function, together with the datum of Tanaka et al., to set limits on the binding energy of ${}^{22}$C for different values of the ${}^{21}$C resonance energy. Our analysis includes a consideration of the higher-order corrections in the EFT, allowing us to set an upper bound on the ${}^{22}$C binding energy which includes both these uncertainties and those in the original measurement. [Preview Abstract] |
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