6 research outputs found
Simulating the weak death of the neutron in a femtoscale universe with near-Exascale computing
The fundamental particle theory called Quantum Chromodynamics (QCD) dictates
everything about protons and neutrons, from their intrinsic properties to
interactions that bind them into atomic nuclei. Quantities that cannot be fully
resolved through experiment, such as the neutron lifetime (whose precise value
is important for the existence of light-atomic elements that make the sun shine
and life possible), may be understood through numerical solutions to QCD. We
directly solve QCD using Lattice Gauge Theory and calculate nuclear observables
such as neutron lifetime. We have developed an improved algorithm that
exponentially decreases the time-to solution and applied it on the new CORAL
supercomputers, Sierra and Summit. We use run-time autotuning to distribute GPU
resources, achieving 20% performance at low node count. We also developed
optimal application mapping through a job manager, which allows CPU and GPU
jobs to be interleaved, yielding 15% of peak performance when deployed across
large fractions of CORAL.Comment: 2018 Gordon Bell Finalist: 9 pages, 9 figures; v2: fixed 2 typos and
appended acknowledgement
Neutron Lifetime Discrepancy as a Sign of a Dark Sector?
We summarize our recent proposal of explaining the discrepancy between the
bottle and beam measurements of the neutron lifetime through the existence of a
dark sector, which the neutron can decay to with a branching fraction 1%. We
show that viable particle physics models for such neutron dark decays can be
constructed and we briefly comment on recent developments in this area.Comment: Talk presented at CIPANP2018. 8 pages, 2 figures; based on: Phys.
Rev. Lett. 120, 191801 (2018) [arXiv:1801.01124]; v2: references adde
Scale setting the M\"obius Domain Wall Fermion on gradient-flowed HISQ action using the omega baryon mass and the gradient-flow scales and
We report on a sub-percent scale determination using the omega baryon mass
and gradient-flow methods. The calculations are performed on 22 ensembles of
highly improved, rooted staggered sea-quark configurations
generated by the MILC and CalLat Collaborations. The valence quark action used
is M\"obius Domain-Wall fermions solved on these configurations after a
gradient-flow smearing is applied with a flowtime of in lattice
units. The ensembles span four lattice spacings in the range fm, six pion masses in the range MeV and multiple lattice volumes. On each ensemble, the gradient-flow
scales and and the omega baryon mass are
computed. The dimensionless product of these quantities is then extrapolated to
the continuum and infinite volume limits and interpolated to the physical
light, strange and charm quark mass point in the isospin limit, resulting in
the determination of fm and fm with
all sources of statistical and systematic uncertainty accounted for. The
dominant uncertainty in this result is the stochastic uncertainty, providing a
clear path for a few-per-mille uncertainty, as recently obtained by the
Budapest-Marseille-Wuppertal Collaboration.Comment: v3: Published version; v2: Added determination of t_0 as well as w_0;
v1: 13 pages plus appendices. The correlation function data, mass results and
analysis code accompanying this publication can be found at this github
repository: https://github.com/callat-qcd/project_scale_setting_mdwf_his
Detailed analysis of excited state systematics in a lattice QCD calculation of
Excited state contamination remains one of the most challenging sources of
systematic uncertainty to control in lattice QCD calculations of nucleon matrix
elements and form factors. Most lattice QCD collaborations advocate for the use
of high-statistics calculations at large time separations ( fm) to combat the signal-to-noise degradation. In this work we
demonstrate that, for the nucleon axial charge, , the alternative strategy
of utilizing a large number of relatively low-statistics calculations at short
to medium time separations ( fm), combined
with a multi-state analysis, provides a more robust and economical method of
quantifying and controlling the excited state systematic uncertainty, including
correlated late-time fluctuations that may bias the ground state. We show that
two classes of excited states largely cancel in the ratio of the three-point to
two-point functions, leaving the third class, the transition matrix elements,
as the dominant source of contamination. On an MeV ensemble,
we observe the expected exponential suppression of excited state contamination
in the Feynman-Hellmann correlation function relative to the standard
three-point function; the excited states of the regular three-point function
reduce to the 1% level for fm while, for the Feynman-Hellmann
correlation function, they are suppressed to 1% at fm.
Independent analyses of the three-point and Feynman-Hellmann correlators yield
consistent results for the ground state. However, a combined analysis allows
for a more detailed and robust understanding of the excited state
contamination, improving the demonstration that the ground state parameters are
stable against variations in the excited state model, the number of excited
states, and the truncation of early-time or late-time numerical data.Comment: v1: 13 pages plus appendices. The correlation function data and
analysis code accompanying this publication can be accessed at this github
repository: https://github.com/callat-qcd/project_fh_vs_3p
Simulating the weak death of the neutron in a femtoscale universe with near-Exascale computing
The fundamental particle theory called Quantum Chromodynamics (QCD) dictates everything about protons and neutrons, from their intrinsic properties to interactions that bind them into atomic nuclei. Quantities that cannot be fully resolved through experiment, such as the neutron lifetime (whose precise value is important for the existence of light-atomic elements that make the sun shine and life possible), may be understood through numerical solutions to QCD. We directly solve QCD using Lattice Gauge Theory and calculate nuclear observables such as neutron lifetime. We have developed an improved algorithm that exponentially decreases the time-to solution and applied it on the new CORAL supercomputers, Sierra and Summit. We use run-time autotuning to distribute GPU resources, achieving 20% performance at low node count. We also developed optimal application mapping through a job manager, which allows CPU and GPU jobs to be interleaved, yielding 15% of peak performance when deployed across large fractions of CORAL