Post on 14-Dec-2015
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Comparison of Chemistry & QCD : K. Wilson (1989 Capri):
“lattice gauge theory could also require a 108 increase in computer power AND
spectacular algorithmic advances before useful interactions with experiment ...”
• ab initio Chemistry1. 1930+50 = 19802. 0.1 flops 10 Mflops3. Gaussian Basis functions
• ab initio QCD1. 1980 + 50 = 2030?*2. 10 Mflops 1000 Tflops3. Clever Multi-scale Variable?
*Fast Computers + Rigorous QCD Theoretical AnalysisSmart Algorithms + = ab initio predictions
“Almost 20 Years ahead of schedule!”
Forces in Standard Model
electron
proton
neutron
quarks
-
+
+
Atoms: MaxwellN=1(charge)
Nuclei WeakN=2 (Isospin)
Sub nuclear: StrongN=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
QED QCD
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
QCD
• QCD: Dirac operator: Aº (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 - 1st 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
FNALWeak 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
http://www.usqcd.org
QDP/C++ Expressions
Can form expressions:
ci(x) = U
ij(x+nu) bj(x) + 2 d
i(x) for all sites x
multi1d<LatticeColorMatrix> 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
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
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% orbitalSo: ~59% from glue
(&/or strange)
Most of mass & spin not from quarks
Caveats:• Missing terms
(disconnected)
Phys. Rev. D77 094502
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 Q2 = 7 GeV2
Highly excited energies:First ever lattice
calculation
Pattern of states ->
Future work:– Separate out decays– Move to physical regime
½+ 3/2+ 5/2+ ½- 3/2- 5/2-
Possible 5/2- state
Phys. Rev. D79 034505
• Charmonium excited spectrum: J-+
• Exotic matter (1-+) radiative decay: large
Spectroscopy
If true with light quarks: Can observe at future JLab Hall D!!
Unknown inexperiment
GeV
Phys. Rev. D77 034501 & to appear PRD