Bulletin of the American Physical Society
APS April Meeting 2017
Volume 62, Number 1
Saturday–Tuesday, January 28–31, 2017; Washington, DC
Session C13: Nuclear Theory |
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Sponsoring Units: DNP Chair: Charles Horowitz, Indiana Univ. Room: Roosevelt 5 |
Saturday, January 28, 2017 1:30PM - 1:42PM |
C13.00001: Few Nucleon Systems From Expanding About the Unitarity Limit Harald W. Griesshammer Can one understand the structure of nuclei at the physical point by an expansion about the unitarity limit? When the $NN$ $S$-wave binding energies are zero, the $NN$ system has no scale. Still, the $3N$ system has one dimensionful quantity $\Lambda_*$, related to the breaking of scale invariance to a discrete scaling symmetry (Efimov effect). The scale is set by the triton binding energy. While qualitatively this has been known for a long time, one may speculate that Nuclear Physics resides then in a sweet spot: bound weakly enough to be insensitive to the details of the nuclear interaction and thus to be described by ``pionless'' EFT; but dense enough that the $NN$ scattering lengths are perturbatively close to the unitarity limit. In this case, $\Lambda_*$ sets the \emph{only} low-energy scale of all observables. Without it, no scale exists, and all nuclei have zero or infinite binding energy in the unitarity limit. For $A\le 4$ nucleons, the spectrum is indeed described well in this simplified version: a converging, perturbative expansion around the unitarity limit, with controlled corrections in the inverse scattering lengths, the interaction ranges and isospin breaking. [1] S.~K{\"o}nig, H.~W.~Grie{\ss}hammer, H.-W.~Hammer, U.~van Kolck: arXiv:1607.04623 [nucl-th]. [Preview Abstract] |
Saturday, January 28, 2017 1:42PM - 1:54PM |
C13.00002: Uncertainty estimates for proton-proton fusion Bijaya Acharya We calculate the proton-proton fusion cross section using chiral effective field theory ($\chi$EFT) and perform a rigorous analysis of the associated uncertainties. The statistical errors in the low-energy constants, which are fitted too scattering and bound-state observables in the pion-nucleon, nucleon-nucleon, and few-nucleon sectors, are propagated to the calculated cross section. We also investigate the sensitivity of the fusion cross section to the high-momentum cutoff of the $\chi$EFT. We extract a value for the zero-energy $S$-factor using a polynomial extrapolant and analyze the errors associated with this procedure. Our result is compared to that of another $\chi$EFT calculation in which the wave functions were represented in a truncated Hilbert space with discrete basis states. [Preview Abstract] |
Saturday, January 28, 2017 1:54PM - 2:06PM |
C13.00003: Effective Field Theory Description of Two-Body Resonance States Jaber Balalhabashi The quantum-mechanical scattering of two particles around a resonance state appears in many areas of physics, for example in cold atoms near narrow, low-lying Feshbach resonances. We construct \cite{ref1} an EFT that describes such scattering with contact, derivative interactions. We demonstrate that a careful choice of leading- and next-to-leading-order terms in an effective Lagrangian gives rise to a systematic expansion of the T matrix around the resonance, with controlled error estimates. We compare phase shifts and pole positions with those of a toy model. We are extending our EFT to include Coulomb interactions with the goal of describing nuclear resonances, such as those appearing in the scattering of alpha particles.\\ \\$[1]$J.~Balalhabashi, S.~Fleming, S.~Sen and U.~van~Kolck, Two-Body Resonances with Effective Field Theory, in preparation. [Preview Abstract] |
Saturday, January 28, 2017 2:06PM - 2:18PM |
C13.00004: Infrared Extrapolations of Electromagnetic Multipole Moments and Transitions Daniel Odell, Thomas Papenbrock, Lucas Platter Basis truncations introduce systematic errors in observables calculated by representing the nuclear Hamiltonian in finite Hilbert spaces. Recent studies of the infrared convergence of finite basis calculations of energies and radii have led to accurate descriptions of numerical data. I will discuss how these concepts can be applied to the study of bound-state quadrupole moments and transitions as well as multipole transitions between bound-states and the continuum. I will show that good agreement is obtained between analytically derived and numerically computed convergence behavior in finite harmonic oscillator spaces for the nucleon-nucleon system. This opens the way to a more precise understanding of structure and reactions involving heavier nuclei. [Preview Abstract] |
Saturday, January 28, 2017 2:18PM - 2:30PM |
C13.00005: Construction of the Nuclear Effective Interaction from Energy Eigenstates and Boundary Conditions Kenneth McElvain, Wick Haxton The original Harmonic Oscillator Based Effective Theory (HOBET) work by Haxton and Luu reduced $H=T+V_{NN}$, with $V_{NN}$ a realistic potential, to $H^{eff}$ in a small basis defined by projection operator {P} while correctly including all scattering by $H$ through an excluded space $Q$. Scattering by $T$ is analytically included to all orders, leaving the ET expansion focused on the short range $V_{NN}$. Results do not depend on the size $P$ as the effect of scattering through $Q$ is fully included, also distinguishing HOBET from other methods. In this talk we abandon $V_{NN}$ and determine the LECs of the ET expansion from energy levels and boundary conditions. In the infinite volume continuum case every energy is an eigenvalue of $H$ with an associated scattering state. In the LQCD context boundary conditions are periodic. In either case the ET LECs can be determined from energy, boundary condition pairs. We show that the Cartesian HO ET LECs can be expressed in terms of the spherical ones, giving a spherical, infinite volume ET, bypassing the use of Luscher's method. The approach cleanly isolates operator mixing induced by the finite box, sequestering effects that vanish in the continuum limit in a Green's function constrained to match the boundary conditions. [Preview Abstract] |
Saturday, January 28, 2017 2:30PM - 2:42PM |
C13.00006: SU(3)-guided Realistic Nucleon-nucleon Interaction for Large-scale Calculations Grigor Sargsyan, Kristina Launey, Robert Baker, Tomas Dytrych, Jerry Draayer We examine nucleon-nucleon (\emph{NN}) realistic interactions, such as JISP16 and N3LO, based on their SU(3) decomposition and identify components of the interactions that are sufficient to describe the structure of low-lying states in nuclei. We observe that many of the interaction components, when expressed as SU(3) tensors, become negligible. Paring the interaction down to its physically relevant terms improves the efficacy of large-scale calculations from first principles (\emph{ab initio}). The work compares spectral properties for low-lying states in \textsuperscript{12}C calculated by means of the selected interaction to the results obtained when the full interaction is used and confirms the validity of the method. [Preview Abstract] |
Saturday, January 28, 2017 2:42PM - 2:54PM |
C13.00007: Ab initio results for intermediate-mass, open-shell nuclei Robert B. Baker, Tomas Dytrych, Kristina D. Launey, Jerry P. Draayer A theoretical understanding of nuclei in the intermediate-mass region is vital to astrophysical models, especially for nucleosynthesis. Here, we employ the \emph{ab initio} symmetry-adapted no-core shell model (SA-NCSM) in an effort to push first-principle calculations across the \emph{sd}-shell region. The \emph{ab initio} SA-NCSM's advantages come from its ability to control the growth of model spaces by including only physically relevant subspaces, which allows us to explore ultra-large model spaces beyond the reach of other methods. We report on calculations for $^{19}$Ne and $^{20}$Ne up through 13 harmonic oscillator shells using realistic interactions and discuss the underlying structure as well as implications for various astrophysical reactions. [Preview Abstract] |
Saturday, January 28, 2017 2:54PM - 3:06PM |
C13.00008: A consistent Analysis of (e,e'p) Reactions through the Nonlocal Dispersive Optical Model Mack Atkinson, Mohammadhossein Mahzoon, Willem Dickhoff, Robert Charity A nonlocal dispersive optical model (DOM) analysis of the $^{40}$Ca(e,e'p)$^{39}$K reaction has been implemented. The real and imaginary potentials are constrained by fitting to elastic-scattering data, total and reaction cross sections, energy level information, and the charge density of $^{40}$Ca. The nonlocality of these potentials permits a proper dispersive self-energy, which accurately describes both positive and negative energy observables. Previous $^{40}$Ca(e,e'p)$^{39}$K calculations, using local non-dispersive potentials employed in a distorted-wave impulse approximation (DWIA), provided the accepted values of 0.65 and 0.5 for the spectroscopic factors of the 0d$\frac{3}{2}$ and 1s$\frac{1}{2}$ orbitals, respectively. These orbitals have well defined spectroscopic factors which can be calculated directly from the DOM self-energy, corresponding to 0.76 and 0.74, respectively. The $^{40}$Ca(e,e'p)$^{39}$K cross sections calculated using the DOM self-energy is in good agreement with the experimental cross sections. These results suggest that a proper description of the (e,e'p) reaction is indeed obtained through the DWIA only by using non-local dispersive optical potentials that simultaneously describe the overlap function and outgoing wavefunction of the proton. [Preview Abstract] |
Saturday, January 28, 2017 3:06PM - 3:18PM |
C13.00009: Pseudoscalar D and B mesons in the hot dense and nonstrange symmetric medium Rahul Chhabra, Arvind Kumar We investigate the effect of temperature and density on the shift in the masses and decay constants of the pseudoscalar $D$ and $B$ mesons in the nonstrange symmetric medium. We use chiral SU(3) model to calculate the medium modified scalar and isoscalar fields $\sigma$, $\zeta$, $\delta$ and $\chi$. We use these modified fields to calculate the in-medium quark and gluon condensates by solving the coupled equations of motions in the chiral SU(3) model. We obtain the medium modified mass and decay constant through these medium modified condensates using the QCD sum rules. Further we use the $^3 P_0$ model by taking the internal structure of the mesons to calculate the in-medium decay width of the higher charmonium states $\chi(3556), \psi(3686)$ and $\psi(3770)$ to the $D \bar{D}$ pairs, through the in-medium mass of $D$ meson and neglecting the mass modification of higher charmonium states. We also compare the present data with the previous results. These results of present investigation may be important to explain the possible outcomes of the experiments like CBM, Panda at GSI. [Preview Abstract] |
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