Engineering topics

Lusk, Ewing

Publications and source records attributed to Lusk, Ewing.

5 records

DOE OSTI2018

Quantum Monte Carlo calculation of neutral-current ν - C 12 inclusive quasielastic scattering

Quasielastic neutrino scattering is an important aspect of the experimental program to study fundamental neutrino properties including neutrino masses, mixing angles, the mass hierarchy and CP-violating phase. Proper interpretation of the experiments requires reliable theoretical calculations of neutrino-nucleus scattering. In this paper we present calculations of response functions and cross sections by neutral-current scattering of neutrinos off $^{12}$C. These calculations are based on realistic treatments of nuclear interactions and currents, the latter including the axial, vector, and vector-axial interference terms crucial for determining the difference between neutrino and anti-neutrino scattering and the CP-violating phase. Here in this paper, we find that the strength and energy-dependence of two-nucleon processes induced by correlation effects and interaction currents are crucial in providing the most accurate description of neutrino-nucleus scattering in the quasielastic regime.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2018

Light-Nuclei Spectra from Chiral Dynamics

In recent years local chiral interactions have been derived and implemented in quantum Monte Carlo methods in order to test to what extent the chiral effective field theory framework impacts our knowledge of few- and many-body systems. Here in this Letter, we present Green’s function Monte Carlo calculations of light nuclei based on the family of local two-body interactions presented by our group in a previous paper in conjunction with chiral three-body interactions fitted to bound- and scattering-state observables in the three-nucleon sector. These interactions include Δ intermediate states in their two-pion-exchange components. We obtain predictions for the energy levels and level ordering of nuclei in the mass range A=4–12, accurate to ≤2% of the binding energy, in very satisfactory agreement with experimental data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2017

Quantum Monte Carlo Calculations in Nuclear Theory

To a remarkable extent, atomic nuclei can be described as collections of point-like particles whose dynamics are dictated by a nonrelativistic Hamiltonian involving two- and three-nucleon potentials.Ab initio approaches are aimed at solving the many-body Schr$ \overline{o} $dinger equation associated with the nuclear Hamiltonian, which is a highly non-trivial problem because of the nonperturbative nature and the strong spin-isospin dependence of the nuclear forces. Within this framework it is possible to disentangle the theoretical uncertainty coming from modeling the nuclear potential and currents from that due to the approximations that are usually inherent in many-body techniques.Our many-body method of choice is quantum Monte Carlo (QMC), in particular Green’s function Monte Carlo (GFMC), which allows solving the nuclear Schrodinger equation with the required 1%accuracy level for both the ground- and the low-lying excited states of A ≤ 12 (A is the number of nucleons) nuclei. Since 2000 we have been achieving excellent agreement with experiment for nuclei with increasing number of nucleons by using the Argonne V18 two-nucleon interaction and the Illinois three-nucleon interactions (AV18+IL7). During this period many other groups have been developing chiral effective field theory (χEFT) potentials; these are generally nonlocal and notsuitable for QMC methods. We and collaborators have recently developed a local χEFT potential including the Δ-isobar degrees of freedom which can be used with QMC.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2017

Evolution of a minimal parallel programming model

Here, we take a historical approach to our presentation of self-scheduled task parallelism, a programming model with its origins in early irregular and nondeterministic computations encountered in automated theorem proving and logic programming. We show how an extremely simple task model has evolved into a system, asynchronous dynamic load balancing (ADLB), and a scalable implementation capable of supporting sophisticated applications on today’s (and tomorrow’s) largest supercomputers; and we illustrate the use of ADLB with a Green’s function Monte Carlo application, a modern, mature nuclear physics code in production use. Our lesson is that by surrendering a certain amount of generality and thus applicability, a minimal programming model (in terms of its basic concepts and the size of its application programmer interface) can achieve extreme scalability without introducing complexity.

97 MATHEMATICS AND COMPUTING↗

NASA NTRS1991

Analyzing high energy physics data using database computing: Preliminary report

A proof of concept system is described for analyzing high energy physics (HEP) data using data base computing. The system is designed to scale up to the size required for HEP experiments at the Superconducting SuperCollider (SSC) lab. These experiments will require collecting and analyzing approximately 10 to 100 million 'events' per year during proton colliding beam collisions. Each 'event' consists of a set of vectors with a total length of approx. one megabyte. This represents an increase of approx. 2 to 3 orders of magnitude in the amount of data accumulated by present HEP experiments. The system is called the HEPDBC System (High Energy Physics Database Computing System). At present, the Mark 0 HEPDBC System is completed, and can produce analysis of HEP experimental data approx. an order of magnitude faster than current production software on data sets of approx. 1 GB. The Mark 1 HEPDBC System is currently undergoing testing and is designed to analyze data sets 10 to 100 times larger.

Baden, Andrew↗