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LQCD SciDAC-4 Project


LQCD SciDAC-4 Project

The Lattice Quantum Chromo-Dynamics (LQCD) SciDAC-4 Project is supported by the U.S. Dept. of Energy Office of Nuclear Physics and the Office of Advanced Scientific Computing Research. The project is supporting the development of the software infrastructure to carry out scientific calculations to address fundamental questions in nuclear science. It is a collaboration of domain scientists, and computer scientists which aims to understand the structure of nuclear matter under extreme conditions, and how quarks and gluons are confined to build the matter that is observed in nature.


News


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Three-pion scattering amplitude selected as an Editor's suggestion

Phys.Rev.Lett. 126 (2021) 012001

For the first time in lattice QCD, a three-hadron scattering amplitude has been determined using a general workflow that does not make use of model assumptions or a perturbative expansion. Focusing on the maximum isospin three-pion channel ($\pi^+ \pi^+ \pi^+ \to \pi^+ \pi^+ \pi^+$) the calculation uses a relativistic finite-volume formalism to relate lattice energies to the physical scattering amplitude. The work has been published in Phys.Rev.Lett. as an Editor’s Suggestion.

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First QCD determination of the decays of a $1^{-+}$ hybrid meson

Phys.Rev.D 103 (2021) 5, 054502

For the first time in lattice QCD, a calculation has shown the presence of an exotic $1^{-+}$ state appearing as an unstable resonance. The result shows that the longstanding model-based proposal that such a state would couple more strongly to the $\pi b_1$ final-state than the lower-lying $\pi \eta, \pi \eta'$ and $\pi \rho$ final-states is confirmed. Possible implications for the recently observed $\pi_1$ experimental candidate state are discussed.

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Correlated Dirac Eigenvalues and Axial Anomaly in Chiral Symmetric QCD

Phys. Rev. Lett. 126, 082001 (2021)

We introduce novel relations between derivatives of the Dirac eigenvalue spectrum with respect to the light sea quark mass and the $(n+1)$-point correlations among the eigenvalues of the massless Dirac operator. Using these relations we present LQCD results for the derivatives at light pion masses and at a temperature of about 1.6 times the chiral phase transition temperature. We find that eigenvalue density develops a peaked structure. We demonstrate that this phenomena is responsible for the manifestations of axial anomaly in two-point correlation functions of light scalar and pseudoscalar mesons. After continuum and chiral extrapolations we find that axial anomaly remains manifested in two-point correlation functions of scalar and pseudoscalar mesons in the chiral limit.

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Lattice QCD constraints on the parton distribution functions of $3^{}{\rm He}_3$

arXiv:2009.05522

The fraction of the longitudinal momentum of $3^{}{\rm He}_3$ that is carried by the isovector combination of $u$ and $d$ quarks is determined using lattice QCD for the first time. The ratio of this combination to that in the constituent nucleons is found to be consistent with unity at the few-percent level from calculations with quark masses corresponding to $m_\pi\sim 800$~MeV, extrapolated to the physical quark masses. This constraint is consistent with, and significantly more precise than, determinations from global nuclear parton distribution function fits. Including the lattice QCD determination of the momentum fraction in the nNNPDF global fitting framework results in the uncertainty on the isovector momentum fraction ratio being reduced by a factor of 2.5, and thereby enables a more precise extraction of the $u$ and $d$ parton distributions in $3^{}{\rm He}_3$.

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Distillation based hadron matrix elements at high momentum

Phys.Rev.D 103 (2021) 3, 034502

Extraction of hadronic observables at finite momenta from LQCD is constrained by the well-known signal-to-noise problems afflicting all such LQCD calculations. In this work we extend the idea of momentum-smearing by exploring modifications to the distillation framework. Together with enhanced time slice sampling and expanded operator bases engendered by distillation, we find ground-state nucleon energies can be extracted reliably for $\vec{p}\le 3$ GeV and matrix elements featuring a large momentum dependence can be resolved.

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NERSC's Cori System Reveals Integral Role of Gluons in Proton Pressure Distribution

NERSC Highlight, 2019-07-08

For the first time, lattice QCD calculations run at NERSC allowed nuclear physicists to determine the pressure distribution inside a proton, taking into account the contributions of the proton’s fundamental particles: quarks and gluons. This discovery brings nuclear scientists closer to a complete understanding of a proton’s structure and the fundamental particles that make up most of the visible matter in the universe.

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MG Proto: Multigrid LQCD Propagators for Multicore x86 systems

SciDAC-4 Highlight, 2019-05-16

A new multi-grid implementation for x86 architectures with supporting AVX512 instructions, such as Intel Xeon Phi Knight's Landing, and Xeon Servers (Skylake and beyond) speeds up calculations by 7x-8x accelerating calculations on platforms such as NERSC Cori KNL, ALCF Theta, TACC Stampede 2 and the Jefferson Lab SciPhi Cluster.

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Summit speeds calculations in the search for exotic particles

OLCF Highlight, 2018-09-17

The accelerated architecture of America’s fastest supercomputer boosts QCD simulations

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Accelerating QCD Gauge Generation on GPUs

SciDAC-4 Highlight, 2018-05-01

The generation of gauge configurations (samples of the strong force field in the vacuum) is the gating first step of nuclear and high energy physics calculations using lattice quantum chromodynamics (LQCD) generating the data on which subsequent calculations depend. Here, we demonstrate a 73x reduction in the GPU-hours required for the generation of such gauge fields moving from Titan to Summit, and incorporating new algorithms well suited to the new system. The improvement on Summit enables calculations which where hitherto considered out-of reach for reasons of computational cost, and will fundamentally re-shape how we will conduct our scientific campaigns in the future.

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Exploring the Exotic World of Quarks and Gluons at the Dawn of the Exascale

Jefferson Lab Highlights, 2017-10-11

Jefferson Lab leads development of next-generation software to benefit nuclear physics computation. An award was recently announced by DOE’s Office of Nuclear Physics and the Office of Advanced Scientific Computing Research in the Office of Science. It will provide $8.25 million for the “Computing the Properties of Matter with Leadership Computing Resources” research project.

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Using Supercomputers to Delve Ever Deeper into the Building Blocks of Matter

Brookhaven National Lab Features, 2017-10-18

Scientists to develop next-generation computational tools for studying interactions of quarks and gluons in hot, dense nuclear matter