1. The Lattice Initiative at Jefferson Lab Robert Edwards Jefferson Lab JLab in a close partnership with MIT has formed the Lattice Hadron Physics Collaboration (LHPC): Members: –R. Brower, C. Rebbi (Boston U.), C. Morningstar (CMU), S. Chandrasekharan (Duke), R. Fiebig (FIU), F.X. Lee (GWU), –R. Edwards, D. Richards, C. Watson (JLab), –S.J. Dong, T. Draper, K.F. Liu (Kentucky), –X. Ji, S. Wallace (Maryland), –P. Dreher, J. Negele, A. Pochinsky (MIT), –M. Burkhardt (NMSU), E. Swanson (Pittsburg), H. Thacker (Virginia)

2. Structure and Interactions of Hadrons Quark and gluon structure of hadrons Spectroscopy of conventional and exotic states of hadrons Interactions between hadrons Fundamental aspects of QCD including confinement and chiral symmetry breaking

3. SciDAC Initiative DOE Scientific Discovery through Advanced Computing Initiative: develop software/hardware infrastructure for next generation computers U.S. Lattice QCD Collaboration consists of 64 senior scientists. Research closely coupled to DOE’s experimental program: –Weak Decays of Strongly Interacting Particles Babar (SLAC) Tevatron B-Meson program (FNAL) CLEO-c program (Cornell-proposed) –Quark-Gluon Plasma RHIC (BNL) –Structure and Interactions of Hadrons Bates, BNL, FNAL, JLab, SLAC Project: $6M for 2001-2003, 30% JLab, 30% FNAL, 15% BNL, 25% universities –Software development & hardware prototyping efforts – no direct physics support

4. National Computational Infrastructure for Lattice Gauge Theory Project: $6M for 2001-2003, 30% JLab, 30% FNAL, 15% BNL, 25% universities –Unify software development and porting efforts for diverse hardware platforms –Hardware prototyping efforts: clusters, QCDOC –No direct physics support

5. Realization of QCD on a lattice Approximate continuous space--time with a 4-dim lattice, and derivatives by finite differences. Theory formulated in Euclidean space. Quarks on sites, gluons on links. Gluons represented by 3x3 complex unitary matrices U m (x) = exp(iga A m (x)) elements of the group SU(3). Gaussian integration over anti- commuting fermion fields y resulted in det(M(U)) and M -1 (U) factors. Gauge action composed of U fields. Approximates continuum:

6. Some Lattice QCD Successes

7. More Successes and Future Expectations

8. Nuclear Physics Future Expectations

9. Precision Tests of the Standard Model Lattice calculations of weak matrix elements are needed to relate experimental results to underlying parameters of the Standard Model Multiple measurements of the same Standard Model parameters in different experiments and calculations will lead to crucial consistency tests In many cases the greatest challenge is to reduce the uncertainties in the lattice calculations

10. Constraints on Standard Model Parameters  and  in Wolfenstein parameterization (1 sigma confidence level) For SM to be correct, they must be in overlap of solid bands Left figure: constraints today Right figure: constraints with existing experimental errors and only improvement in lattice uncertainties to 3%

11. Confinement and Model Predictions - Static Quark Potentials Models propose different mechanisms for confinement Static quark potential (potential between infinitely massive quarks forming mesons) in different representations can discriminate among the models Perturbative Casimir scaling hypothesis well describes non-perturbative lattice data: for Casimir C D in representation D=3,6,8,… Claimed to rule out models like Bag and Instanton – scaling different Flux tube counting also inconsistent Bali, 99

12. Hadron Spectrum – Benchmark of Lattice QCD Spectrum of lowest lying states is the benchmark of LQCD Most extensively pursued lattice calculation Quenched spectrum agrees with experiment to 10% Inconsistency in meson sector apparently resolved in full QCD Systematic uncertainties: –Finite volume: V   –Continuum extrapolation: a  0 –Chiral extrapolations: M PS  M  Calculation ~ 50 Gflops-years. In 1999 largest NERSC allocation 2 Gflop-years GF11, CPPACS 99

13. Excited Baryons Describing N * spectrum gives vital clues about dynamics of QCD and hadronic physics –Role of excited glue –Quark-diquark picture –Quark interactions Open mysteries: –Nature of Roper? –  (1405) mass? –Missing resonances? History of lattice studies of excited baryons quite brief. Recent work using improved gauge and fermion actions Lattice Representations Continuum spin reducible under three irreducible ray representations of the cubic group Rep.Continuum spin reps G 1 1/2, 7/2, … H3/2, 5/2, 7/2, … G 2 5/2, 7/2, …

14. Gluonic States of Matter Glueballs: quenched glueball –Surprising result: masses closer to 2 GeV instead of 1 GeV Hybrid mesons: big focus of JLab (and lattice group!) –Spin exotic mesons are J PC states not accessible in quark model –Characterized by excited glue or perhaps four-quark states Lattice calculations of light exotic meson states still first generation (noisy)! –Lightest 1 -+ exotic roughly 2GeV –Considerably higher than experimental candidates 1.4, 1.6 GeV Morningstar & Peardon 99

15. Moments of Nucleon Quark Distributions JLab/MIT-Adelaide: 1 st three non-trivial moments of non- singlet unpolarized quark distribution u-d in the proton: Calculation ~ 10’s of Gflops- years Chiral extrapolation sensitive to small quark mass Factor of 2 decrease in error bars in 2 weeks! Prediction for transversity dist:

16. Hardware Plans Simplifying features of lattice QCD calculations make building specially designed computers far more cost effective than buying commercial ones –Uniform grids –Regular, predictable communications Two hardware tracks: –QCD On a Chip (QCDOC) –Commodity Clusters Each track has its own strength Each track may prove more optimal for different aspects of our work The two track approach positions us to exploit future technological advances, and enables us to retain flexibility

17. Commodity Clusters Market forces are producing rapid gains in processor and memory performance –Moore’s Law  60% growth in performance per year –Pentium 4 currently provides exceptional performance for QCD Market for interconnects is growing Open Source System Software –Flexible programming environment –SciDAC Scalable Systems Software Targeted price-performance JLab acquisitions: –NOW: 128 node/myrinet P4 cluster; ~ 130 Gflops –Late summer: probably 256 P4 node/3-dim. GigE mesh; > 200 Gflops FY 2002FY 2003FY 2004FY 2005FY 2006 $/Mflops3.32.01.20.90.7

18. Deployment Plan QCDOC –FY 2003: 1.5 Tflops (Columbia) –FY 2003-4: 5.0 Tflops (BNL) Clusters –FY 2002-3: 0.5 Tflops (FNAL, JLab) –FY 2004: 1.0 Tflops (FNAL, JLab) –FY 2005: 6.0 Tflops (FNAL, JLab) –FY 2006: 8.0 Tflops (FNAL, JLab) Planning for 22 Tflops by 2006 Hope to obtain funding from HEP, NP, and SciDAC programs Funding at a higher level would accelerate research, and enable U.S. leadership in lattice QCD

19. The Competition Theorists in Europe and Japan are moving rapidly to obtain resources comparable to those we propose –The APE Collaboration will begin deploying multi-teraflops computers in 2003 –UKQCD will acquire a 5.0 Tflops (sustained) QCDOC in 2003 –DESY plans to acquire a 20.0 Tflops (peak) APE NEXT in 2004 We need to act now to deploy the infrastructure required for terascale simulations of QCD

20. Conclusions JLab lattice group actively pursuing calculations of –Excited baryon spectroscopy –Exotic/hybrid meson spectroscopy –Elastic E&M nucleon electric and magnetic form factors –Anticipate calculations of  Precise calculations commensurate with experimental program require: –Measure a large number of correlators –Sufficiently light pions to resolve pion cloud –Large physical volumes –Continuum extrapolation –Full QCD SciDAC efforts: –Software/hardware infrastructure development –Follow-on deployment of large terascale systems