Yoshinobu Kuramashi
Center for Computational Sciences (CCS)
University of Tsukuba
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Contents
§ 1. Members of Particle Physics Group
§ 2. Introduction to Lattice QCD
§ 3. PACS-CS Project
PRD79(2009)034503, PRD80(2009)054502, arXiv:0911.2561
§ 4. Summary and Future Perspectives
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Members of Particle Physics Group
Staff
N.Ishizuka, Y.K., Y.Taniguchi, T.Yoshié
PD
Y.Namekawa, N.Ukita, T.Yamazaki
OB
Y.Iwasaki: ex-President of the University of Tsukuba (2004-2009) ex-Director of CCP (1992-1998)
A.Ukawa: Executive Advisor to the President ex-Director of CCP and CCS (1998-2007)
Collaborative members
S.Aoki, K.Kanaya
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Introduction to Lattice QCD investigate nonperturbative effects of the strong interaction through numerical simulations with lattice QCD strong interaction one of the fundamental forces in Nature
(gravity, electromagnetic, strong, weak) dynamics between quarks and gluons quark proton neutron nucleon
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6 Flavors of Quarks and Gluons charge +2/3 u
−1/3 d c s s t b quark
(R,B,G) gluons
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Various Hadrons baryon (3 quarks) p, n, Δ, Λ, Σ, Σ ＊ , Ξ, Ξ ＊ , Ω, Λc, Ξc, Λc, ... meson (quark and anti-quark)
π, K, K ＊
, ρ, ω, η, φ, a, b, f, D, B, ...
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QCD Lagrangian determine kinematics and interactions of quarks and gluons quark mass m q
(q=u,d,s,c,b,t) are free parameters
Is it possible to quantitatively describe the hierarchical structures with an appropriate tuning of m q
?
quarks hadrons nuclei
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Lattice QCD nonperturbative investigation of strong interactions with respect to
QCD Lagrangian
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Path Integral Formalism numerical integration with Monte Carlo method on discretized 4-dim. space-time lattice average over the values evaluated on configurations
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History before PACS-CS
1981 first calculation of hadron masses in quenched approx.
(Hamber-Parisi) demonstrate the possibility of first principle calculations
1996-2000 precision measurements in quenched approx.
(CP-PACS) clear deviation from experimental values
2000-2005 embark on 2+1 flavor QCD simulations
(CPPACS/JLQCD, MILC, RBC, …) attempt of first principle calculations
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CP-PACS/JLQCD project
2+1 flavor QCD simulations with HMC algoriyhm
CP-PACS/JLQCD m ud
=0 m ud
=∞ looks impossible to reach the physical point in near future
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PACS-CS project aim to make simulations at the physical point of 2+1 flavor QCD
Physicists
S.Aoki, N.Ishizuka, K.Kanaya, Y.K. Tsukuba
Y.Namekawa, Y.Taniguchi, A.Ukawa,
N.Ukita, T.Yamazaki, T.Yoshié
K.-I.Ishikawa, M.Okawa Hiroshima
T.Izubuchi BNL
Computer scientists
T.Boku, M.Sato, D.Takahashi, O.Tatebe Tsukuba
T.Sakurai, H.Tadano
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PACS-CS
P arallel A rray C omputer S ystem for C omputational S ciences
2560 nodes, 14.3 Tflops peak, 5.12 TB memory operation started on 1 July 2006 at CCS in U.Tsukuba
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T2K-Tsukuba
T ukubaT okyoK yoto open supercomputer alliance
648 nodes, 95.4 Tflops peak, 20.7 TB memory operation started on 2 June 2008 at CCS in U.Tsukuba
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Algorithmic Improvements drastic reduction of computational cost thanks to DDHMC algorithm physical point simulations are within reach
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Toward the Physical Point nontrivial curvature = log dependence expected from chiral symmetry importance of simulations at smaller ud quark masses
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Comparison with Experiment hadron masses extrapolated at the physical point m
π
, m
K
, m
Ω inputs ⇒ consistent within 2-3 % error bars
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Fine Tuning to the Physical Point reweighting method simulation: (m ud
,m s
) ⇒ physical point: (m ´ ud
,m ´ s
) with m ud
≃ m ´ ud and m s
≃ m ´ s reweighting factors
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Comparison with Experiment hadron masses normalized by m
Ω m
π
/m
Ω
, m
K
/m
Ω are properly tuned (Δm ud
<1 MeV, Δm s
<3MeV)
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Summary and Future Perspective peak machine target physics
< 1TF CP-PACS embark on 2+1 flavor QCD
10 TF PACS-CS physical point simulation
100 TF T2K-Tsukuba determination of QCD parameters light nuclei in quenched QCD
(Yamazaki et al., arXiv:0912.1383)
10 PF NGSC light nuclei in 2+1 flavor QCD finite temperature and finite density
1 EF NNGSC weak hadron matrix elements w/o OPE heavy nuclei in 2+1 flavor QCD
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Why Physical Point Simulations?
simulations at heavier quark masses (m

>200~300MeV) and extrapolations to the physical point with ChPT current most popular strategy due to computational cost what’s wrong with cheaper strategy?
・ guiding principle for chiral extrapolation?
ChPT is not always valid for all the physical quantities polynomial is valid only near the physical point
・ difficult to precisely trace logarithmic curvatures
・ different dynamics at unphysically heavy quark masses
ρ→ππ decay is not allowed
・ final destination is 1+1+1 flavor QCD simulations
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