Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session MM: Nuclear Theory VII |
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Chair: Andreas Metz, Temple University Room: White Hill |
Wednesday, October 13, 2021 4:00PM - 4:12PM |
MM.00001: Three-pion scattering from lattice QCD Raul A Briceno, Maxwell Hansen, Robert Edwards, Christopher Thomas, David Wilson The majority of QCD states are unstable resonances that couple strongly to multi-particle channels, with a significant fraction of these coupling to asymptotic three-particle states. Lattice QCD, being a framework that incorporates all dynamical coupling non-perturbatively, provides a promising pathway toward studying the excitations of the theory. Although challenging, lattice QCD calculations of systems composed of three-hadrons are finally being performed. In this talk, I present a calculation by the Hadron Spectrum Collaboration, Phys.Rev.Lett. 126:012001 (2021), which is the first to go from the lattice QCD correlation functions to the desired infinite-volume scattering amplitudes. I review outstanding challenges to study the low-lying resonances of QCD that couple to three particles. |
Wednesday, October 13, 2021 4:12PM - 4:24PM |
MM.00002: Charge-exchange transitions from the ab initio symmetry-adapted no-core shell model Grigor H Sargsyan, Kristina D Launey, Tomas Dytrych, Jerry P Draayer The symmetry-adapted no-core shell model (SA-NCSM) utilizes emergent symmetries in nuclei in order to reduce the dimensionality of the model space. This, in turn, allows one to reproduce the low-energy nuclear dynamics with only a small fraction of the model space, and hence making solutions to heavier nuclei and ultralarge model spaces feasible. The symmetry-adapted basis of the SA-NCSM is well suited for describing electromagnetic and beta-decay transitions enabling us to perform calculations for up to pf-shell nuclei. This work discusses calculations of recoil-order corrections in analyses of beta decay experiments for 8Be that probe fundamental symmetries as well as calculations of neutrinoless double beta decay matrix elements necessary to study whether neutrinos are their own antiparticles. |
Wednesday, October 13, 2021 4:24PM - 4:36PM |
MM.00003: Deuteron-induced nuclear reactions within a Faddeev framework using ab initio interactions 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,γ) cross sections on unstable targets. The deuteron-nucleus system can be treated as a three-body system consisting of the neutron, proton, and the nucleus. While Faddeev techniques enable the exact description of the three-body dynamics, 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. To study and quantify the uncertainties, the three-body model should to be grounded in the underlying many-body theory. To proceed, we adopt the no-core shell model (NCSM) coupled with the resonating group method (RGM) approach to compute effective nucleon-nucleus interactions and construct a three-body Hamiltonian from the pairwise interactions. We present momentum space Faddeev calculations of observables for 6Li ground state and deuteron-alpha scattering using the microscopic interactions derived from the NCSM/RGM. To gain further insight on the Faddeev description of deuteron-nucleus systems, we contrast our results with those obtained directly from the NCSM/RGM approach. |
Wednesday, October 13, 2021 4:36PM - 4:48PM |
MM.00004: Spin-group reclassification of neutron resonances Gustavo P Nobre, David A Brown, Sophia J Hollick, Sergey Scoville, Pedro J Rodriguez Fernandez, Mary Fucci, Rose-Marie A Crawford, Sergio Ruiz The evolution of the many elements formed in the Universe, from hydrogen and helium, to the ones heavier than iron, and their relative abundance, continues to be one of the main sources of scientific interest today. The different processes known in astrophysics to govern these successions of nuclear formation and decay, r-process and s-process, depend strongly on nuclear properties such as the intrinsic density of levels of a given nucleus and how they behave when emitting or absorbing particles such as neutrons, protons and/or photons. There are few experimental constraints that we can use to narrow down such properties and most of the information we know comes from experimental measurements of resonance states seen in compound nuclei formed by neutron-induced reactions. Therefore, a proper and reliable account of all resonances is crucial for the description of nuclear reactions. We have developed a Machine-Learning method, the Bayesian Resonance Reclassifier, to make use of the statistical properties of resonances to train an algorithm capable to identify missing and misassigned resonances. We are able to train the model on synthetic data and use transfer learning to assess resonance sequences from the Atlas of Neutron Resonances, evaluated files or experimental data. |
Wednesday, October 13, 2021 4:48PM - 5:00PM |
MM.00005: Partial pressures of hadron families in lattice QCD Angel R Nava, Claudia Ratti, Alejandro Florez Lattice QCD simulations provide the pressure of QCD as a function of the temperature. In the low-temperature regime, the thermodynamics can be understood in terms of a gas of non-interacting hadrons and resonances, but the contribution of the single hadronic species cannot be easily isolated [1]. We propose linear combinations of susceptibilities of conserved charges, that isolate the contribution of hadrons to the pressure of QCD according to their baryon number B, electric charge Q and strangeness S content. We test the validity of these linear combinations in the Hadron Resonance Gas (HRG) model and compare them to available lattice QCD results. |
Wednesday, October 13, 2021 5:00PM - 5:12PM |
MM.00006: Electric Polarizability of Hadrons from Lattice QCD Hossein Niyazi, Andrei Alexandru, Frank X Lee Electric and magnetic polarizabilities are two of the fundamental properties of hadrons which help us understand the distribution of charge and currents inside hadrons and how they respond to external electromagnetic fields. For nucleons, these values are determined experimentally from Compton scattering. For charged pions, the experiments are more challenging since no free pion target is available and the results are less precise, but a number of experiments are planned that will improve the accuracy. Lattice QCD can be used to compute hadron properties as determined by quark and gluon dynamics, providing results that are complementary to other theoretical approaches. In this talk I will review the lattice QCD methods used to compute hadron polarizabilities, focusing on electric polarizability, and present our results. |
Wednesday, October 13, 2021 5:12PM - 5:24PM Not Participating |
MM.00007: Nuclear equation of state from the in-medium similarity renormalization group with numerical extrapolations and symmetry guided optimizations Yani C Udiani The nuclear equation of state (EOS) is of great interest because it ties nuclear structure calculations to astrophysical observables. The in-medium similarity renormalization group (IMSRG) is an iterative and non-perturbative operator diagonalization method that calculates total energies of a many body system using a nucleon-nucleon interaction. In this work, the IMSRG is used to calculate the EOS using the chiral N2LO optical potential. The IMSRG transformations are done in a finite box with finite basis functions- which introduces uncertainties in computed energies. To avoid finite size effects, it is essential to maximize the used model space. This becomes computationally expensive rapidly. Hence, it is of interest to extract and exploit information about the system at the operator level. In this talk, I will introduce our recent work numerically extrapolating to converged IMSRG energies using a few sample points. I will discuss subtle simplifications to IMSRG transformations due to emergent symmetries from a plane wave basis. Moreover, I will show the equation of state calculated with the IMSRG using the N2LO optical potential. |
Wednesday, October 13, 2021 5:24PM - 5:36PM |
MM.00008: Normalizing flows for microscopic calculations of the nuclear equation of state Pengsheng Wen, Jeremy W Holt, Jack Brady The nuclear equation of state (EOS) at finite temperature is fundamental to describe the properties of medium-energy heavy-ion collisions as well as the hydrodynamic evolution of core-collapse supernovae and neutron star mergers. Microscopic calculations of the hot and dense matter equation of state using state-of-the-art nuclear two-body and three-body forces in many-body perturbation theory are numerically challenging due to the repeated evaluation of high-dimensional integrals across varying density, temperature, and composition. In this talk, we demonstrate that normalizing flows provide a suitable Monte Carlo integration framework for such microscopic EOS calculations. Normalizing flows are a class of machine learning models used to construct a complex distribution from a simple base distribution and thus can be used to generate highly expressive representations of the integrands that appear in high-order many-body perturbation theory calculations. Moreover, a normalizing flow model trained on one target integrand can be easily transferred as the density, temperature, or even nuclear potential is varied. |
Wednesday, October 13, 2021 5:36PM - 5:48PM |
MM.00009: Modern Inelastic Scattering Descriptions: Deformed QRPA Excited State Transitions Emanuel V Chimanski, Jutta E Escher, Sophie Péru, Walid Younes Reaction rates and particle absorption are of fundamental importance in the study of the origin of elements and in applied areas such as radio isotopes production and radiation therapies. For example, inelastic scattering calculations can provide direct and indirect information about reactions involving unstable targets, systems where measurements cannot be performed due to the fast decay of the nuclei involved. Therefore, theoretical models are required to supplement and if necessary even provide the desired nuclear data. The deformation of the recent nuclei of interest increases the complexity of the calculations and challenges the usual assumptions present in the standard reaction models. We are extending the predictive power of nuclear reaction calculations by combining a modern reaction formulation with the state-of-the-art nuclear structure description for deformed targets. We use a projection formalism to restore angular momentum and utilize the transition density formalism to describe relevant nuclear structure in an axially deformed QRPA (Quasi-Particle Random Phase Approximation) framework. Folding with an effective interaction allows us to achieve inelastic scattering predictions. One of our objectives is to obtain cross sections for data evaluations and enable the indirect determination of neutron capture cross sections for s-process branch points. Capture cross sections for s-process branch points will be combined with isotopic analyses of pre-solar grains, carried out by the Stardust collaboration at LLNL, will provide valuable constraints on models of stellar evolution. |
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