USQCD project    July, 1 2006---June, 30, 2008

Background:

• 2007-8 Proposal submitted to the US lattice QCD Scientific Program Committee, asking for time on the QCDOC machine at BNL. Includes preliminary results showing reduction in taste breaking for HYP-smeared fermions compared to asqtad-fermions. Proposal was granted 3.25 Million node-hours on the QCDOC
• Abstract:   This is a class B proposal, asking for time on the QCDOC to continue our calculation of kaon matrix elements using improved staggered quarks. Our major focus will be on a calculation of $B_K$, which is of particular interest to constraining elements of the CKM matrix, and on the related matrix elements $B_7^{3/2}$ and $B_8^{3/2}$, which enter into the prediction for $\epsilon'/\epsilon$. The present (2006-7) allocation should allow completion of work on the MILC coarse lattices, and possibly a start on the fine lattices. We propose to extend this work to all the MILC fine configurations. The valence propagators will be HYP-smeared staggered fermions. On each lattice we will calculate with 10 different valence quark masses, allowing 55 kaon masses, so as to provide sufficient data points for fitting to the rather elaborate form predicted by staggered chiral perturbation theory. We propose in parallel to calculate the spectrum determining in particular the masses of flavor non-singlet pions of all tastes. This information is needed as input into the chiral perturbation theory fits to B_K, B_7 and B_8 and also will provide cross-checks on the applicability of staggered chiral perturbation theory. We expect that graduate students, and possibly also postdoctoral associates, at both the University of Washington and Seoul National University will contribute to this project.

  We are requesting 3.35 Mnode-hours on the QCDOC.

• 2006-7 Proposal submitted to the US lattice QCD Scientific Program Committee, asking for time on the QCDOC machine at BNL. Proposal was granted 1.2 Million node-hours on the QCDOC.
• Abstract:   We propose to calculate kaon matrix elements of four-fermion operators using improved staggered quarks. Our major focus will be on a calculation of B_K, which is of particular interest to constraining elements of the CKM matrix, and on the related matrix elements B_7^(3/2) and B_8^(3/2), which enter into the prediction for epsilon'/epsilon. We propose to use the MILC coarse and fine Asqtad configurations, and calculate valence propagators using HYP-smeared staggered fermions. On each lattice we will calculate with 10 different valence quark masses, allowing 55 kaon masses, so as to provide sufficient data points for fitting to the rather elaborate form predicted by staggered chiral perturbation theory. We also propose a parallel spectrum (and possibly also decay constant) calculation, determining in particular the masses and decay constants of flavor non-singlet pions of all tastes. This information is needed as input into the chiral perturbation theory fits to B_K, B_7 and B_8 and also will provide cross-checks on the applicability of staggered chiral perturbation theory. The output of the proposed calculation will be a result for B_K and other kaon matrix elements with all errors controlled.

  We are asking for CPU time on the QCDOC, since our codes are built on the Columbia Physics System, and use the level-3 QCD-API routines for the QCDOC. We are asking for a total of 1.2 Million node-hours, so that this is a ``class B'' proposal.

  We expect that graduate students, and possibly also postdoctoral associates, at both the University of Washington and Seoul National University will contribute to this project.

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Updates (most recent first)

• 1-22-08:   Matrix element and spectrum calculation on 28^3 x 96 fine lattices (m_l/m_s=0.0062/0.0031) continue: about 400 (out of 512) configurations completed, using both cubic U(1) and cubic wall sources for spectrum calculation. Analysis underway to determine size of taste-breaking in spectrum.

  Some coarse lattice data was missing and has been recalculated.

  Publication on taste-splitting reduction by HYP smearing submitted to the "arXiv".

• 10-31-07:   Matrix element and spectrum measurements completed on desired coarse MILC lattice ensembles (m_l/m_s = 0.010/.050, .010/.030, 0.007/.050, 0.020/.050, 0.030/0.050). Analysis underway.

  Matrix element and spectrum calculation on 28^3 x 96 fine lattices (m_l/m_s=0.0062/0.0031) underway: about 200 (out of 512) configurations completed. Using both cubic U(1) and cubic wall sources for spectrum calculation.

• 7-16-07:   Matrix element and spectrum calculation updates: 20^3 x 64 m_l/m_s = 0.01/0.03 ensemble complete; 20^3 x 64 0.03/0.05 ensemble almost complete (475 out of 564 configurations); 246 configurations of 24^3 x 64 m_l/m_s = 0.005/0.05 lattices completed.

  Coulomb gauge fixing on 28^3 x 96 lattices progressing: 273 (out of 531) 0.0124/0.031 configurations and 260 (out of 573) .0062/0.031 configurations are fixed.

• 4-19-07:   Running on 20^3 x 64 m_l/m_s = 0.01/0.03 ensemble almost complete; starting on 24^3 x 64 m_l/m_s = 0.005/0.05 lattices.
• 3-22-07:   Running on 20^3 x 64 m_l/m_s = 0.01/0.05 and 0.02/0.05 ensembles complete. Speeded up code by dropping one of sink operators in spectrum calculation (as gave redundant information).
• 2-07:   Tests complete. Production begun on five 128 node partitions. Code speeded up by moving propagators into memory to reduce I/O.
• 1-07:   Spectrum test complete. B_K test indicates sporadic corruption by hardware failure---solved by restarting calculation on given configuration if failure. Gauge fixing ongoing.
• 8-9-06:   Production test underway. Calculation of full spectrum and matrix elements, with 55 pairs of quark masses, on a subset of 20^3 x 64 MILC lattices (m_l/m_s = 0.01/0.05) underway on both Seoul National University (SNU) cluster and on QCDOC. If they agree, we are ready to move to a production run on QCDOC. Choice of wall source turned out, in preliminary work at SNU, to be unimportant, and we have chosen a U(1) cubic source.
• 8-9-06:   210 gauge configurations from MILC ensemble MILC_2064f21b676m010m050 (coarse lattices of size 20^3 x 64 with m_s=0.05 and m_ud=0.01) have been fixed to Coulomb gauge. This was done on 1 mother board (64 node) of QCDOC, run as a test job.Timing 1-3 hrs/lattice.
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Links

• Information on Lattice physics at Seoul National University .
• Plenary talk at Lattice 2006 by Weonjong Lee on Kaon physics, including discussion of results from this project.
• Poster at Lattice 2006 by T. Bae, J. Kim, W. Lee and S. Sharpe on spectrum with HYP improved staggered fermions. The results demonstrate the efficacy of HYP smearing in reducing taste-symmetry breaking.
• Poster at Lattice 2006 by T. Bae, J. Kim, W. Lee and S. Sharpe showing status of unquenched calculation of matrix elements using HYP-smeared staggered fermions.
• Plenary talk at Lattice 2006 by Stephen Sharpe discussing the status of dynamical simulations with staggered fermions, and in particular discussing the validity of the fourth-root trick used in such simulations.
• Presentation of this proposal by Stephen Sharpe at US LQCD All Hands Meeting, Fermilab, April 2006.
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Steve Sharpe < sharpe@phys.washington.edu> Last modified: 8/10/06