kab/sc-pac2001-6.19.01 operated by the jefferson science associates for the u.s. department of...

kab/SC-PAC2001-6.19.01

Operated by the Jefferson Science Associates for the U.S. Department of Energy

Thomas Jefferson National Accelerator Facility

SURA 2006

Session II: Lattice Spectroscopy

David Richards (JLAB)



SURA 2006

Spectroscopy - I

• Classic tool for gleaning information about degrees of freedom of QCD

• Experimental and ab initio N* and Hybrid programs aim at discovering effective degrees of freedom of QCD, and resolving competing low-energy models:

Capstick and Roberts, PRD58 (1998) 074011

Timely opportunity for lattice QCD in concert with EBAC



SURA 2006

Variational Method

• Given N £ N correlator matrix C(t) = h 0 j O(t) O(0) j 0 i, one

defines the N principal correlators i(t,t0) as the eigenvalues of

where t0 (the time defining the “metric”) is small

• Principal effective masses defined from correlators plateau to

lowest-lying energies

min ( En – Ei)

• Eigenvalues ! energies• Eigenvectors ! “wave functions”



SURA 2006

Glueball Spectrum

Morningstar and Peardon



SURA 2006

Spectroscopy - III

Application of Variational Method in trial calculation allows extraction of up to eight excited states

Quenched QCD calculation of nucleon spectrum

LHPC, hep-lat/0609052

New thrust: generation of full QCD lattices using anisotropic clover action for spectroscopy



SURA 2006

Illustration: Roper Resonance

Physics at physical values of the pion mass very different from the heavy-quark regime – chiral perturbation theory

•Roper resonance at light quark massesS.J. Dong et al, •Bayesian statistics and constrained curve fitting•Used simple three-quark operator• Roper predominantly a three-quark state?

a ~ 0.2 fm



SURA 2006

Cost of Computation

Jansen et al,POS (LAT2005) 118

Major effort at Resonance spectroscopy of both Hybrids and baryons



SURA 2006

Hybrids and GlueX - I

• GlueX will photoproduce hybrid mesons in Hall D.

• Lattice QCD has a crucial role in both predicting the spectrum and in computing the production rates – Jo Dudek

• Only a handful of studies of hybrid mesons at light masses – mostly of 1-+ exotic• Variational method to enable comprehensive computation low-lying meson spectrum



SURA 2006

Hybrids and GlueX - II

resonance, X

• An important realization of JLab Theorists was that lattice QCD enabled calculation of photocouplings• Guide experimental program as to expected photoproduction rates.

• Initial exploration in Charmonium• Good experimental data• Allow comparison with QCD-inspired models• Lattice computations pioneered at JLab



SURA 2006

PDGCLEO

Photocouplings - I

• Recent study of transitions between conventional mesons, e.g. S ! V

Dudek, Edwards, Richards, PRD73, 074507

Not used in the fit

lat.

Lattice

Expt.



SURA 2006

Photocouplings - II

Q2-dependence inspired by NR

potential model with rel.

corrections:

13

First computation of exotic meson resonance spectrum, and of 1-+ photocouplings, at pion masses down to 220 MeV

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