Lattice-based Studies of QCD.

Transcription

1 Lattice-based Studies of QCD. David Richards Jefferson Laboratory QCD and Hadron Physics Town Meeting, Temple, Sept , 2014!!!!! Thanks: R. Briceno, W. Detmold, M. Engelhardt, K-F Liu, S. Meinel, M. Savage + JLab colleagues

2 Outline Lattice : Theory and Computation Achievements and Opportunities Spectrum of QCD The structure of hadrons The NN Interaction (Polarizabilities) (Isospin breaking) (Fundamental Symmetries). Initiatives and Resources

3 Nuclear Interacti ons Science Infrastructure Software Scidac ê f H0L 1 mn f H1L 1T Hadron Structure HGeVL Sivers-Shift, u-d - quarks 0.0 z` = 0.39, -0.2»b T» = 0.24 fm, -0.4 m p = 518 MeV ò DY SIDIS ô Spectroscopy negative parity h»v» Hlattice unitsl positive parity exotics Lattice QCD INCITE Leadership-class USQCD Facilities Clusters + GPUS + BG/Q GlueX energy reach 0.5 3

4 The Spectrum of QCD 4

5 Low-lying Hadron Spectrum Benchmark of LQCD Durr et al., BMW Collaboration Science 2008 Control over: Quark-mass dependence Continuum extrapolation finite-volume effects (pions, resonances)

6 Spectroscopy: Isoscalar Meson Spectrum Dudek et al, arxiv: , arxiv: Report to NSAC: Implementing the 2007 LRP A key part of the 12-GeV physics program at Jefferson Lab is the ability to produce these exotic hybrid mesons using photon beams, which is expected to generate unprecedented numbers of these particles. The GlueX experiment in the new Hall-D is poised to carry out this program using a detector designed to tackle just this problem. The GlueX experimental program is coupled with both detailed lattice QCD predictions and the strong support of the Jefferson Lab theory center in analyzing and interpreting the expected new data. This puts the U.S. in a unique position to explore this important new science made possible by the 12 GeV CEBAF Upgrade... J. Dudek et al., PRD73,

7 Excited Baryon Spectrum Broad features of SU(6)xO(3) symmetry. Counting of states consistent with NR quark model. Inconsistent with quark-diquark picture or parity doubling. [56,0 + ] [70,1 - ] [56,0 + ] [70,1 - ] [70, 0 + ], [56, 2 + ], [70, 2 + ], [20, 1 + ] N 1/2+ sector: need for complete basis to faithfully extract states 7

8 What we have learned.. Common mechanism in meson and baryon hybrids: chromomagnetic field with Eg GeV Subtract ρ Subtract N 8

9 Future Opportunities - I Luescher: energy levels at finite volume phase shift at corresponding k Matrix in l det h e 2i (k) U k L 2 i =0 lattice irrep Feng, Renner, Jansen, PRD83, PACS-CS, PRD84, Alexandru et al Lang et al., PRD84, Resonant I = 1 ππ Phase Shift Dudek, Edwards, Thomas, Phys. Rev. D 87, (2013) 9

10 Future Opportunities - II 180 (a) 180 (c) Dudek, Edwards, Thomas, Wilson, PRL (in press) Extend to inelastic channels: Guo et al, Briceno et al., First lattice calculations of inelastic channels Lattice QCD will predict results before or during GlueX 10

11 Singularities complex plane 11

12 Meson photoproduction R. Gothe Recent developments to make lattice QCD calculation possible: Briceño [JLab], Hansen & Walker-Loud [JLab/W&M] (2014) QED Agadjanov,Bernard, Meißner & Rusetsky (2014) p p p p p p p N

13 The Structure of Hadrons 13

14 Three-Dimensional Imaging 5D Wigner distributions 3D 1D

15 Isovector Charge Radius Green et al, arxiv: Precision Calculations of the Fundamental Quantities in Nuclear Physics - at physical quark masses

16 Origin of Nucleon Spin contributions to nucleon spin DSu+d L u+d m p 2 D HERMES (2007) contributions to nucleon spin DSu 2 DSd m 2 2 D L d L u LHPC, Haegler et al., Phys. Rev. D 77, (2008); D82, (2010) Total orbital angular momentum carried by quarks small Orbital angular momentum carried by individual quark flavors substantial.

17 Origin of Nucleon Spin - II 17

18 Parametrizations of GPDs Provide phenomenological guidance for GPD s CTEQ, Nucleon Form Factors, Regge Comparison with Diehl et al, hep-ph/ Important Role for LQCD

19 Transverse momentum distributions (TMDs) from experiment, e.g., SIDIS (semi-inclusive deep inelastic scattering) + DY HERMES, COMPASS, JLab 12 GeV, RHIC-spin, EIC, DY incoming proton hadronizing quark jet of hadrons P h incoming electron jet of hadrons final state interactions fragmenting proton remnant time Bernhard Musch 2011 final state interactions! explain large asymmetries otherwise forbidden! signature of QCD! 19

20 TMDs in Lattice QCD k y k u u xp z P z B. Musch, PhD Thesis; Haegler, Musch, Negele, Schafer arxiv: k x d = = Z Z z Z d(n k) Z d(n k) Introduce Momentum-space correlators d 4 l 2(2 ) 4 e ik l (l; P, S) d 4 l 2(2 ) 4 e ik l hp, S q(l) Uq(0) P, Si continuum U P exp ig d µ A µ ( ) 0 along path from 0 to Choice of path - retain gauge invariance SIDIS: path runs to infinity Lattice: equal time slice

21 Slide: A. Bacchetta Worm gears on the lattice P. Hägler, B. U. Musch, J. W. Negele, and A. Schäfer, Europhys. Lett. 88 (2009) 61001

22 Transverse momentum distributions (TMDs) Lattice QCD B. Musch et al., Phys.Rev. D85 (2012) ; M. Engelhardt, Lattice

23 Flavour-separated Hadron Physics Doi et al. (ChQCD Collaboration), arxiv: , PRD79:094502,2009 Strangeness contribution to electric and magnetic form factors. G s M (Q2 ) κ ud = κ ud = κ ud = Q 2 (GeV 2 ) G s E (Q2 ) κ ud = κ ud = κ ud = Q 2 (GeV 2 ) Uncertainties: statistical, Q 2 dependence, chiral extrapolation G s M (0) = 0.017(25)(07)

24 Strange-quark contribution to hadron spin QCDSF, arxiv: s MS ( p 7.4 GeV) = 0.020(10)(4) Small, negative contribution In general, Quark and gluons mix under renormalization ln µ 2 q S g = s (µ 2 ) 2 The local operators mix as follows: Pqq 2n f P qg P gq P gg q S g

25 Flavor-separated and Gluon Contributions PRELIMINARY: S. Meinel, Lattice 2014 Complete calculation of flavor-separated and gluonic contributions to nucleon spin Deka et al, arxiv:

26 Parton Distributions in LQCD Formulation of LQCD in Euclidean space precludes direct calculation of light-cone correlation functions LQCD computes Moments of parton distributions New ideas: calculations of QUASI-distributions in infinite-momentum frame x,y Detmold, Melnitchouk, Thomas Large P z q(x, µ, P z )= Z dz 4 e izk X. Ji, Phys. Rev. Lett. 110, (2013). X. Ji, J. Zhang, and Y. Zhao, Phys. Rev. Lett. 111, (2013). J. W. Qiu and Y. Q. Ma, arxiv: D ~P (z) z e ig R z 0 A z(z 0 )dz 0 (0) ~ P Equal time correlator E

27 q(x, µ, P z )= Flavor Structure Z dy y Z x y, µ P z q(y, µ)+o 2 QCD P 2 z, M 2 N P 2 z! +... H.W. Lin et al, arxiv: First lattice calculations of Quasi Distributions q(x)! q(x) smallest x ' 1/a 12 GeV; Future EIC Violation of Gottfried sum rule d(x) > ū(x)

28 NN Interactions and Nuclei { { (Lattice) QCD Many-body methods, EFT, GFMC, NCSM.. 28

29 H-Dibaryon Bound state of two (strange) baryons uuddss, originally proposed by Jaffe (1977) BH HMeVL NPLQCD : nf=2+1 HALQCD : nf= BH HMeVL NPLQCD : nf=2+1 HALQCD : nf= m p 2 HGeV 2 L m p 2 HGeVL Evidence for weakly bound or just unbound dibaryon 29

30 Nuclear Physics from QCD is Possible! s = 0 s = 1 s = Binding energies at physical strange-quark mass B [MeV] body 3-body 4-body d nn 3 He 4 3 n H 3 He 3 He He H-dib n He 4 He

31 The Structure of Hadrons in Nuclei How is the structure of a hadron modified in medium? Calculation of magnetic moments of lightest nuclei. Experimentally measured values NPLQCD, arxiv: m ' 800 MeV Differences from naive shell model

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33 SUMMARY Person, Moment, Machine Amalgam of new ideas, algorithmic advances, and peta- and exa-scale computers: lattice QCD essential to fulfill NP mission.! Spectrocopy: Calculations of resonances that can confront experimental analysis. Electromagnetic Properties. Structure: Calculations of the fundamental properties at the physical quark masses. GPDs, TMDs, + Lattice QCD + Expt greater than each alone. An ab initio understanding of the NN interactions - properties of hadrons in nuclei