Nuclear Physics in the SciDAC Era Robert Edwards Jefferson Lab SciDAC 2009 TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: AAAAAA

Comparison of Chemistry & QCD : K. Wilson (1989 Capri): “ lattice gauge theory could also require a 10 8 increase in computer power AND spectacular algorithmic advances before useful interactions with experiment...” ab initio Chemistry = flops  10 Mflops 3.Gaussian Basis functions ab initio QCD = 2030?* 2.10 Mflops  1000 Tflops 3.Clever Multi-scale Variable? * Fast Computers +Rigorous QCD Theoretical AnalysisSmart Algorithms + = ab initio predictions “Almost 20 Years ahead of schedule!”

Forces in Standard Model Atoms: Maxwell N=1(charge) Nuclei Weak N=2 (Isospin) Sub nuclear: Strong N=3 (Color) Standard Model: U(1) £ SU(2) £ SU(3)

Quantum Chromo Dynamics - QCD QED: theory of electromagnetism QCD: theory of strong interactions – hadronic physics QEDQCD Photon,  Gluons, G Charged particles, e, , u, d,… Quarks: u, d, s, c, b, t 2 charges: positive & negative 3 charges: “red”, “green”, “blue” Photon is neutral Gluons carry color charge  e ' 1/137  s ' O(1) Highly non-linear theory – can only use perturbation theory at high energy

Quark+anti-Quark in Meson

Energy in glue

3 Color  3 quarks in Proton

QCD QCD: Dirac operator: A º (vector potential), m (mass), ° º (4x4 matrices) Lattice QCD: finite difference Probability measure: Observables:

Gauge generation How to produce gauge fields? Hamilton’s eq’s - 1 st order coupled diff. eq’s) Bummer! –Must be “reversible” –No adaptive time steps Total energy in gauge/quark fields Momentum

Cost Scaling Cost: reasonable statistics, box size and “physical” pion mass Extrapolate in lattice spacings: 10 ~ 100 PF-yr PF-years

USQCD National Effort US Lattice QCD effort: Jefferson Laboratory, BNL and FNAL FNAL Weak matrix elements BNL RHIC Physics JLAB Hadronic Physics SciDAC – R&D Vehicle Cluster Prototyping Software R&D Impact on DOE ’ s Nuclear Physics Program

SciDAC Software QCD friendly API’s/libs Application codes High level (Linpack-like) Data parallel (C/C++) Linear algebra, threading, comms Code generators

QDP/C++ Expressions Can form expressions: c  i (x) = U  ij (x+nu) b  j (x) + 2 d  i (x) for all sites x multi1d U(Nd); LatticeFermion c, b, d; int nu, mu; c = shift(u[mu],FORWARD,nu)*b + 2*d; QDP++ code (data-parallel) Template based Shifts use QMP for face comms Level-1 BLAS-like linear algebra core

Critical code: Dirac operator/inverter Critical codes: develop special API and libraries Example: Dirac operator []

Threading/Multi-core Hybrid threads/MPI Impact: –Coalesce messages –Better perf. –Cache- coherency latency EXPENSIVE

Scaling on Cray XT4 (ORNL) Socket level threading improved performance threads+mpi mpi Work involving RENCI

Acceleration Deflation & multigrid – big speedups JLab/W&M (SciDAC) + TOPS

Nuclear Physics & Jefferson Lab Lab doubling beam energy Adding new experimental Hall CD-3 JLab Receives DOE Approval to Start Construction of $310 Million Upgrade

Nuclear Structure Fundamental questions –Size, shape, distribution of charge and current in hadrons –Quark and gluon distributions –How does nucleon spin arise from quarks and gluons? –What role do strange quarks play in nucleon structure? Status –Basic nucleon properties calculated with 5-10% precision. –Pursuing higher precision, more demanding properties. NP 2014 milestone –Perform lattice calculations in full QCD of nucleon form factors, low moments of nucleon structure functions and low moments of generalized parton distributions, including flavor and spin dependence.

Nuclear Structure Spin of the proton? ~41% quark spin (u+d) ~0% orbital So: ~59% from glue (&/or strange) Most of mass & spin not from quarks Caveats: Missing terms (disconnected) Phys. Rev. D

Spectroscopy Spectroscopy reveals fundamental aspects of hadronic physics. –Essential degrees of freedom? –Gluonic excitations in mesons - exotic states of matter? Status. –Can extract excited nucleon energies & identify spins, –Pursuing calculations in full QCD with realistic quark masses. Crucial complement to 12 GeV program at JLab. –Excited nucleon spectroscopy. –GlueX: flagship search for gluonic excitations.

Nucleon spectrum NP2012 milestone: Spectrum & E&M transitions up to Q 2 = 7 GeV 2 Highly excited energies: First ever lattice calculation Pattern of states -> Future work: –Separate out decays –Move to physical regime ½+½+ 3/2 + 5/2 + ½-½- 3/2 - 5/2 - Possible 5/2 - state Phys. Rev. D

Exotic matter? Can we observe exotic matter? Excited string QED QCD

Charmonium excited spectrum: J -+ Exotic matter (1 -+ ) radiative decay: large Spectroscopy If true with light quarks: Can observe at future JLab Hall D!! Unknown in experiment GeV Phys. Rev. D & to appear PRD

Outlook Software infrastructure developed for Lattice QCD –Enabled effective utilization of INCITE resources Lattice QCD’s impact on Nuclear Physics –Nucleon structure (protons, neutrons) –Spectroscopy Results relevant to U.S. DOE experimental programs Unifying Nuclear Physics research