Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session S13: Few Body Systems & Related TopicsLive
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Sponsoring Units: GFB Chair: James Colgan, LANL |
Monday, April 19, 2021 1:30PM - 1:42PM Live |
S13.00001: New Measurements of Neutron-Neutron Quasifree Scattering in Neutron-Deuteron Breakup Ronald Malone, Alexander Crowell, Laurie Cumberbatch, Brent Fallin, Forrest Friesen, Calvin Howell, Collin Malone, Ethan Mancil, David Ticehurst, Werner Tornow, Benjamin Crowe, Diane Markoff, Henryk Witala The neutron-deuteron (nd) system is a rich environment for testing models of nucleon-nucleon and three-nucleon (3N) interactions. Ab-initio calculations of 3N scattering observables accurately describe most experimental data. One exception is the cross section for neutron-neutron (nn) quasifree scattering (QFS) in nd breakup. Recent measurements of this cross section reveal that theory underpredicts the data by more than 15\%. These results imply charge-symmetry breaking at a level higher than expected. We have conducted two new measurements of the nn QFS cross section. In the first experiment an uncollimated beam of 10.0 MeV neutrons was used. The second experiment was performed with a collimated beam of 15.6 MeV neutrons. Time-of-flight techniques were used to determine the energies of the breakup neutrons detected in coincidence. Our measurements differ from previous experiments in that the beam-target luminosity was determined from the nd elastic scattering yields measured concurrently with the breakup yields. Experimental methods and results will be discussed. [Preview Abstract] |
Monday, April 19, 2021 1:42PM - 1:54PM Live |
S13.00002: The Exchange Force in a System of Three Non-identical Particles Roman Kezerashvili, Igor Filikhin, Suslov Vladimir, Branislav Vlahovic We study the bosonic $K^0K^+K^-$ system by using the isospin independent nuclear potentials [1]. The $K^0K^+K^-$ represents $ACB$ or $AAB$ particle models with or without Coulomb potential. For the latter case if one neglects the $AA$ interaction, $V_{AA}$=0, the system can be described by the Faddeev equation as $(H_0+V_{AB}-E)W=-V_{AB}PW$, where P is the permutation operator. The term on the r. h. side of the equation is the exchange term, which has a clear physical interpretation (see, for example, [2]). This term adds negative energy to the two-body energy $E_2$ defined by the l. h. side of the equation and $E=E_3 |
Monday, April 19, 2021 1:54PM - 2:06PM Live |
S13.00003: Faddeev approach to deuteron-induced nuclear reactions with ab initio potentials Linda Hlophe, Sofia Quaglioni Deuteron-induced nuclear reactions are an essential tool for probing the structure of stable and rare isotopes as well as extracting quantities of astrophysical interest such as (n,$\gamma$) cross sections on unstable targets. While Faddeev techniques enable the exact description of the dynamics within a three-body model, their application to deuteron-induced reactions on rare isotopes is complicated by the unavailability of nucleon scattering data needed to constrain the corresponding effective nucleon-target interactions. Moreover, the use of phenomenological potentials with ambiguous off-shell properties introduces further uncertainties. In order to understand and quantify the uncertainties, we apply the Faddeev theory to light deuteron-nucleus systems that are within the reach of state-of-the-art ab initio reaction theories. We present Alt-Grassberger-Sandhas (AGS) momentum space calculations of observables for deuteron-induced reactions on $^4$He using microscopic interactions derived from the no-core shell model (NCSM) coupled with the resonating group method (RGM). [Preview Abstract] |
Monday, April 19, 2021 2:06PM - 2:18PM Live |
S13.00004: Applying the Eigenvector Continuation Method for Two-Body Scattering in Momentum Space Patrick Millican, Alberto Garcia, Richard Furnstahl, Xilin Zhang In previous work we implemented eigenvector continuation (EC) for two-body scattering in coordinate space using the Kohn variational method. EC is a technique that uses eigensolutions for several sets of known parameters to form a basis that can be used to accurately interpolate and extrapolate solutions for the same Hamiltonian with different parameters. We applied EC to Hamiltonians for multiple physical potentials with different traits. EC was shown to be computationally efficient for exploring parameter space, making it attractive to use as an emulator in data science. Here we will demonstrate that EC is also viable as an emulator for two-body scattering when formulated in momentum space by applying it to a variety of potentials. [Preview Abstract] |
Monday, April 19, 2021 2:18PM - 2:30PM Live |
S13.00005: Short-range correlation physics at low RG resolution Anthony Tropiano, Dick Furnstahl, Scott Bogner Recent experiments have succeeded in isolating processes where short-range correlation (SRC) physics is dominant and well accounted for by SRC phenomenology. But an alternative and compelling picture emerges from renormalization group (RG) evolution to low RG resolution. At high RG resolution, SRCs are identified as components in the nuclear wave function with relative momenta above the Fermi momentum. Evolution to lower resolution shifts SRC physics from nuclear structure to the reaction operators without changing the measured observables. We show how the features of SRC phenomenology manifested at high RG resolution are cleanly identified in factorized form with simple two-body operators and local-density calculations using simple structure. We verify that the experimental consequences follow directly from well-established properties of nucleon-nucleon interactions such as the tensor force. [Preview Abstract] |
Monday, April 19, 2021 2:30PM - 2:42PM Live |
S13.00006: Predictive Calculations Of Nuclear Reactions With Tthe No-Core Shell Model With Continuum Konstantinos Kravvaris, Sofia Quaglioni, Petr Navratil The accurate modeling of nuclear reaction cross sections relevant in stellar processes is one of the main goals of reaction theory. In the light-element region, first-principles calculations where all nucleons are treated as active are possible, allowing for predictive calculations to be made. However, calculations performed with modern nuclear interactions derived from chiral effective field theory have inherent uncertainties; namely the truncation of the chiral expansion, as well as possible uncertainties arising from fitting low-energy constants to experiment. It is therefore essential to be able to quantify such uncertainties in order for a theoretical prediction of reaction cross sections to be made. We will outline the basics of the no-core shell model with continuum and present preliminary results for astrophysical reactions and efforts to quantify their uncertainties. [Preview Abstract] |
Monday, April 19, 2021 2:42PM - 2:54PM Live |
S13.00007: From few to many: thermodynamics with up to seventh-order virial coefficients Yaqi Hou, Joaquin Drut The thermodynamics of dilute quantum systems is captured at high temperatures by the virial expansion (VE). In the VE, order by order, the few-body dynamics enters into the many-body dynamics. The 2nd-order virial coefficient is calculated by analyzing the 2-body problem, which results in the celebrated Beth-Uhlenbeck formula. For the n-th order coefficient, one analyzes the n-body problem and sums over energy eigenstates. For those reasons, it was only in the 21st century that precise 3rd-order calculations first appeared. To tackle this problem, we developed a new non-perturbative, non-stochastic computational method and applied it to spin-1/2 Fermi gases with short range attractive interactions. Our answers reproduce previous results for the 3rd-order coefficient from weak coupling to the unitary limit and resolve a long-standing tension between theory and experiment for the 4th-order coefficient. In this contribution we present new estimates up to 7th order for the first time, which allow us to use resummation techniques and calculate the density and magnetization equations of state, Tan's contact, and static response, all of them at zero and finite polarization. Our method can be generalized to harmonically trapped systems, studies of quench dynamics, and neutron matter. [Preview Abstract] |
Monday, April 19, 2021 2:54PM - 3:06PM Not Participating |
S13.00008: A new viewpoint to Faddeev equations Mohammadreza Hadizadeh, Mahdi Radin The inputs for the Faddeev equations, in three-body bound and scattering calculations, are two-body transition operators $t(\epsilon)$. The Lippmann-Schwinger equation should be solved to obtain the matrix elements of $t(\epsilon)$ for negative or positive two-body subsystem energies $\epsilon$, where the values of $\epsilon$ are dictated by the magnitude of Jacobi momentum of the third particle. The solution of the Lippmann-Schwinger equation is challenging, mainly for positive energies where the singularities occur. In this talk, we propose a new form of Faddeev equations for three-body bound state calculations by working directly with two-body interactions and avoiding calculating the matrix elements of two-body $t-$matrices. We test the new formalism in both nonrelativistic and relativistic descriptions of three-body bound states in a three-dimensional approach, without using a partial wave decomposition. The calculated nonrelativistic and relativistic three-body binding energies in the proposed novel Faddeev scheme are in excellent agreement with the results of traditional Faddeev formalism. [Preview Abstract] |
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