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Lattice QCD and CLQCD Activities

Lattice QCD and CLQCD Activities. Ying Chen Institute of High Energy Physics, CAS Weihai, August 10, 2010. Outline. Overview of lattice QCD Selected latest physical results of LQCD Standard model parameters alpha_s current quark masses

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Lattice QCD and CLQCD Activities

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  1. Lattice QCD and CLQCD Activities Ying Chen Institute of High Energy Physics, CAS Weihai, August 10, 2010

  2. Outline • Overview of lattice QCD • Selected latest physical results of LQCD Standard model parameters alpha_s current quark masses CKM matrix elements relevant Spectroscopy Nucleon structure Nuclear physics • CLQCD activities • Summary

  3. I. Overview of lattice QCD Lattice QCD: A path integral formalism of QCD on Euclidean spacetime Dynamical Calculation Otherwise, a unitary theory of full QCD on the lattice Observables: VEV of operators, such as Green’s functons. Monte Carlo simulation, importance sampling

  4. Sources of systematical uncertainties: • Pion masses are higher than the physical value • chiral extrapolation • Finite lattice spacing: continuum extrapolation • Finite volume effects.

  5. Ukawa, KITPC 2009

  6. Ukawa, KITPC 2009

  7. Ukawa, KITPC 2009

  8. Lattice QCD Experiments Dynamical configurations Facilities Expensive Probe1 Probe2 ……… Detectors Fairly expensive Probes: valence quark propagators, etc., Manpower intensive Data analysis Data analysis Offline data analysis

  9. RBC-UKQCD Collaboration: • 2+1 Domain Wall Fermions (DMF) Advantage: chiral symmetry on the lattice

  10. MILC Collaboration: • 2+1 Staggered Fermions (Asqtad) Advantage: computationally cheap Disadvantage: the fourth-root-trick is controversial.

  11. 2+1 Wilson-type Fermions (Clover,etc.) Disadvantage: chiral symmetry can be restored only in the continuum limit.

  12. ETMC Collaboration: • nf=2 (2+1+1) Twisted Mass Fermions (Asqtad)

  13. II. Selected Latest Results of LQCD • Standard model parameters • alpha_s • current quark masses • CKM matrix elements relevant • Spectroscopy • Nucleon structure • Nuclear physics

  14. 1. Standard Model parameters • Strong coupling constant 3-loop PT expressions of these quantities. A set of short distance quantities, such as Wilson loops, which can be obtained From lattice QCD Convert to MS scheme, and then running to the M_Z scale.

  15. Quark masses

  16. For heavy quark masses, HPQCD proposes a new solution C. McNeile et al, arXiv:1004.4285

  17. Latest results of quark masses C. T. H. Davies et al. (HPQCD Collab.), arXiv:0910.3102[hep-ph]

  18. CKM matrix elements relevant CKM matrix and PDG number (Amsler2008) Lattice gold-plated processes which can be used to determine the CKM matrix elements

  19. Master equation: Decay constants, Form factors Decay constants: Which can be derived from the two-point function,

  20. Form factors

  21. Aubin et al 2005

  22. a) Latest results of f_pi and f_K E. E. Scholz, PoS(LAT2009)005

  23. b) Latest results of f_D and f_Ds Grey bands indicate the HPQCD results (Kronfeld 2010)

  24. c) Latest results of f_B and f_Bs

  25. d) Other lattice inputs to CKM Current status of lattice inputs to the global fit of the CKM unitarity triangle. These are obtained by averaging all available 2+1 flavor results documented in proceedings and publications that contain Complete error budgets, and account forcorrelations between different calculations in a conservative manner.

  26. 2. Hadron spectroscopy • Light hadron spectrum S. Aoki et al. (PACS-CS Collab.) Phys. Rev. D 79, 034503 (2009). S.Durr et al.(BMW Collab.), Science 322, 1224 (2008).

  27. Lattice predictions of heavy flavored hadrons

  28. Charmonium spectrum and hyperfine splitting 2+1 DMF sea and overlap valence (chiQCD preliminary)

  29. Rho resonance On the finite lattice,

  30. Pion-pion I=1, L=1 phase shift and BW fit (G. Shierholz, arXiv:0810.5337(hep-lat))

  31. 3. Summary • High precision for standard model parameters. • The spectrum of quite a few light hadrons can • be reproduced. • Further efforts desired for most of hadron • resonances. • Lattice calculation at the physical point is • expected in the following ten years.

  32. II. Lattice QCD in China

  33. 中国格点QCD合作组 (CLQCD) 研究人员: 马建平（ITP, CAS）刘 川（Peking Univ.) 刘玉斌(Nankai Univ.)张剑波(Zhejiang Univ.） 陈莹(IHEP, CAS) 研究生+ 博士后

  34. CLQCD 计算资源 1. 目前可用计算资源(？？？？？？？）： 深腾7000（中国科学院网络信息中心超级计算中心) 120TFLOPs 曙光5000（上海超级计算中心) 200 TFLOPs TOP500排15位, 2. 未来可用计算资源（？？？？？？？）： PETAFLOP机器——比如“天河1号”

  35. 在国际上排第五位

  36. CLQCD 的研究领域 1. 与BEPCII/BESIII的物理实验密切结合 轻强子性质 奇特强子态（如胶球、混杂态等） 粲夸克物理 • Charmonium radiative decays (quenched • and unquenshed) • D meson masses and decay constants 2. 有限温度有限密度QCD

  37. J/psi radiative decays to glueballs • QCD predicts the existence of glueballs • Quenched LQCD predicts glueball spectrum • Lowest-lying glueballs have masses in • the range 1~3GeV • Experimentally, f0(1370), f0(1500), • f0(1710),etc.,are glueball candidates, • but decisive conclusion cannot be drawn. • Due to its abundance of gluons, J/psi • radiative decay can be the best hunting • ground. • BESIII in Beijing is producing J/psi • events Y. Chen et al, Phys. Rev. D 73, 014516 (2006)

  38. Numerical details • Formalism The decay width of J/psi radiatively decaying to the scalar glueball can be derived from the formular where E1(0) is the on-shell form factor, which appears in the matrix elements (J.J. Dudek,hep-lat/0601137) With the vector current insertion , these Matrix elements can be calculated through the three point function,

  39. Lattice and parameters Anisotropic lattice: Strong coupling: • 5000 gauge configurations, separated by 100 HB sweeps • Charm quark mass is set by the physical mass of J/psi • On each configuration, 96 charm quark propagators are • calculated with point sources on all the 96 time slices. • The periodic boundary conditions are used both for the • spatial and temporal directions.

  40. The form factor and the decay width Polynomial fit: The branch ratio is

  41. Experimental results for J/psi radiatively decaying to scalars C. Amsler et al., Phy. Lett. B667, 1 (2008)

  42. The systematic uncertainties • The continuum extrapolation • has not been carried out. • (The same calculation on a • finer lattice is undergoing.) • The lattice vector current has not been renormalized. • (We are working on it.) • The uncertainty owing to the quenched approximation. • ( Cannot be resolved in the near future.) • The analyses of tensor channel and pseudoscalar are • under the way.

  43. Thank You!

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