Bulletin of the American Physical Society
2020 Fall Meeting of the APS Division of Nuclear Physics
Volume 65, Number 12
Thursday–Sunday, October 29–November 1 2020; Time Zone: Central Time, USA
Session SJ: Mini-Symposium: Nuclear Physics from Effective Field Theory and Lattice Field Theory V |
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Chair: Huey-Wen Lin, MSU |
Sunday, November 1, 2020 10:30AM - 10:42AM |
SJ.00001: Bayesian analysis of EFTs with Jupyter notebooks R.J. Furnstahl Uncertainty quantification (UQ) is an essential part of applying effective field theories (EFT) to low-energy nuclear physics. A Bayesian statistical framework is particularly well suited for this task, as EFT expectations regarding naturalness and truncation errors can be encoded through prior probability distribution functions (PDFs). The specification of priors means that all theoretical assumptions are explicit in the calculation of the posterior PDFs, making such an analysis reproducible. The BUQEYE collaboration (``Bayesian Uncertainty Quantification: Errors for Your EFT'') has the overall goal of full UQ and associated diagnostics for EFT predictions using Bayesian statistics. The BUQEYE website https://buqeye.github.io/ has freely available Python code, Jupyter notebooks, and cheatsheets to make reproducing and extending our results easy. In this talk we provide a guide to this material. [Preview Abstract] |
Sunday, November 1, 2020 10:42AM - 10:54AM |
SJ.00002: Posterior Shrinkage by Intelligent Design: An Application to Proton Compton Scattering Harald W. Griesshammer Interpreting measurements requires a theory. Its accuracy varies with energy. To optimize experimental design, and so to ensure that the substantial resources of modern experiments acquire the most valuable data, both the theory uncertainty and the expected experimental errors must be considered. We apply a Bayesian approach to proton Compton scattering. Chiral Effective Field Theory ($\chi$EFT) is used to infer the electromagnetic polarizabilities of the nucleon from data. With increasing photon energy, both experimental rates and sensitivities to polarizabilities ncrease, but the accuracy of $\chi$EFT decreases. Our physics-based model of truncation errors is combined with present knowledge of the polarizabilities and assumptions about experimental capabilities at HI$\gamma$S and MAMI. We assess the information gain from specific observables at specific kinematics: by how much are new data apt to shrink uncertainties? The strongest gains are in two spin observables at $\omega\simeq140$ to $200$\,MeV, and tightly constrain $\gamma_{E1E1}-\gamma_{E1M2}$. New cross sections between $100$ and $200$\,MeV will substantially improve $\alpha_{E1}-\beta_{M1}$, $\gamma_\pi$ and $\gamma_{M1M1}-\gamma_{M1E2}$. Such data is pivotal to pin down the scalar and spin polarizabilities. [Preview Abstract] |
Sunday, November 1, 2020 10:54AM - 11:06AM |
SJ.00003: Gluon distribution functions in the nucleon from lattice QCD Raza Sufian We report on our calculation of the unpolarized and polarized gluon parton distribution functions (PDFs) in the nucleon using short-distance QCD factorization of lattice QCD matrix elements . The computation is performed on a $32^3 \times 64$ isotropic lattice with a pion mass of 360 MeV and lattice spacing, a = 0.094 fm using 2+1 flavor of Clover-Wilson fermion. In order to reduce the statistical fluctuations, the gluonic operators are smeared using gradient flow and the renormalized matrix elements are extracted by taking the small flow-time limit. Finally the lattice QCD matrix elements are factorized to the $\overline{MS}$ scheme PDFs in the light-cone $z^2\to 0$ limit, using next-to-leading order perturbative matching formula. [Preview Abstract] |
Sunday, November 1, 2020 11:06AM - 11:18AM |
SJ.00004: Uncertainty estimates for muon capture on the deuteron Jose Bonilla, Bijaya Acharya, Lucas Platter Muon capture on the deuteron is a two-body electroweak process that can provide information on the properties of the electroweak current in nuclear effective field theory but also the three-body force in the nuclear Hamiltonian. I will discuss recent progress on the calculation of the rate for this process and corresponding uncertainty estimates. [Preview Abstract] |
Sunday, November 1, 2020 11:18AM - 11:30AM |
SJ.00005: $\mathbf{\beta}$-delayed proton emission from $\mathbf{^{11}}$Be in effective field theory Wael Elkamhawy, Zichao Yang, Hans-Werner Hammer, Lucas Platter We investigate the rare decay of $^{11}$Be into $^{10}$Be $+$ $p$ $+$ $e^-$ $+$ $\bar{\nu}_e$ using Halo effective field theory (Halo EFT), thereby describing the process of beta-delayed proton emission. The branching ratio for this decay mode in $^{11}$Be remains an important unsolved problem. Here, we will consider the weak decay of the valence neutron of the halo nucleus $^{11}$Be into the continuum for the first time within Halo EFT. We assume a shallow 1/2$^+$ resonance in the $^{10}$Be$-p$ system with an energy and width consistent with a recent experiment. Our results show that the experimental measurements of branching ratio and resonance parameters are consistent with each other. Thus, no exotic mechanism (such as beyond the standard model physics) is needed to explain the experimental decay rate. [Preview Abstract] |
Sunday, November 1, 2020 11:30AM - 11:42AM |
SJ.00006: Bayesian Model Averaging for Extrapolation of Effective Field Theory Expansions Matthew Connell, Daniel Phillips, Ian Billig Bayesian Model Averaging (or BMA) is used to combine the predictions of different Bayesian models in a statistically consistent way. As such it can improve predictive performance and provide an assessment of model uncertainty, which is otherwise difficult to quantify. BMA weather forecasts are more accurate than forecasts using a particular meteorological model, as in [1]. Here we want to assess the usefulness of BMA as an extrapolation tool for EFT expansions. We apply BMA to a toy model EFT expansion. We perform Bayesian fitting for polynomials of different degree on this toy model, and apply BMA to obtain an averaged extrapolating model. Then we test how well these agree with pseudo-data. By doing this for different underlying functions, different model priors, and different extrapolation distances we formulate some general principles regarding the usefulness of BMA in this context. [1] "Using Bayesian Model Averaging to Calibrate Forecast Ensembles" (Raftery et al. 2003) [Preview Abstract] |
Sunday, November 1, 2020 11:42AM - 11:54AM |
SJ.00007: Nucleon-Nucleus Global Optical Potential from Chiral Effective Field Theory Taylor Whitehead, Jeremy Holt, Yeunhwan Lim We formulate a global microscopic nucleon-nucleus optical potential from many-body perturbation theory based on chiral two- and three-body forces. The nucleon self-energy is calculated in homogeneous matter to second order in perturbation theory, which gives the central real and imaginary terms of the optical potential. The full nucleon-nucleus optical potential is derived within the improved local density approximation utilizing mean field models consistent with the chiral nuclear force employed. A selection of chiral forces is used and theoretical uncertainties are accounted for. Each term of the optical potential is then fit to the standard Woods-Saxon form. Functional forms of the depth and shape parameters that depend on projectile energy, mass number, and isospin asymmetry are derived. This microscopic global optical potential is calculated from the local optical potentials of all stable nuclei within 16≤A≤208 and 0≤E≤200 MeV. In future works we plan to include nuclei off of stability. Assumptions and potential shortcomings of conventional global optical potentials are examined. Lastly we compare the results of the microscopic calculations to phenomenological models and experimental data. [Preview Abstract] |
Sunday, November 1, 2020 11:54AM - 12:06PM |
SJ.00008: Constraining the nonanalytic terms of the nuclear symmetry energy with chiral nuclear forces. Pengsheng Wen, Jeremy W. Holt The nuclear symmetry energy, defined as the difference between the pure neutron matter energy per particle and the symmetric nuclear matter energy per particle at a fixed density, is crucial for understanding the properties of neutron-rich nuclei and neutron stars. The expansion of the nuclear symmetry energy in even powers of the isospin asymmetry has recently been shown to breakdown in beyond-mean-field-theory calculations of the nuclear equation of state. In this talk we will describe a new finite difference method to extract the fourth- and sixth-order regular and logarithmic contributions to the nuclear symmetry energy starting from microscopic chiral two- and three-body forces. We find that in general the expansion coefficients of the nonanalytic logarithm terms are larger in magnitude than those of the corresponding regular (even-power) terms for the energy from the second-order perturbation calculation. [Preview Abstract] |
(Author Not Attending)
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SJ.00009: Light-nuclei electroweak interactions in pionless effective field theory Hilla Deleon Low-energy electroweak interactions in light nuclear systems (deuteron, $^3$H, $^3$He) take part in many scenarios, such as magnetic moments, $\beta$-decay, Big Bang nucleosynthesis and the evolution of the Sun, which is a result of a fusion of two protons into deuteron (named $pp$ fusion) that determines the Sun's lifetime ($\sim 10^9$ years). Here, we use a general perturbative diagrammatic approach for calculating electroweak interactions between $A=2,3$ nuclei. Using the four well-measured electromagnetic reactions, we introduce a novel uncertainty assessment to estimate truncation effects, which enables us to estimate the theoretical uncertainty of the theory. This theoretical uncertainty, accompanied by the strong analogy between the electromagnetic and weak observables, led to the high accuracy calculation of the $pp$ fusion rate. This prediction for the $pp$ fusion rate is up to 5\% bigger than previous estimates, which might affect current models of solar evolution. [Preview Abstract] |
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