Q. Mason

Publications (15)14.74 Total impact

• Source

  Available from: arxiv.org

  Article: Charm physics with highly improved staggered quarks

  C. T. H. Davies, E. Follana, K. Hornbostel, G. P. Lepage, Q. Mason, H. Trottier, J. Shigemitsu, K. Wong
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  ABSTRACT: We use a relativistic highly improved staggered quark action to discretize charm quarks on the lattice. We calculate the masses and the dispersion relation for heavy-heavy and heavy-light meson states, and show that for lattice spacings below .1 fm, the discretization errors are at the few percent level. We also discuss the prospects for accurate calculations at the few percent level of f_D_s, f_D, and the leptonic width of the psi and phi.
  11/2006;
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  Available from: arxiv.org

  Article: Highly Improved Staggered Quarks on the Lattice, with Applications to Charm Physics

  E. Follana, Q. Mason, C Davies, K. Hornbostel, G. P. Lepage, J. Shigemitsu, H. Trottier, K. Wong
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  ABSTRACT: We use perturbative Symanzik improvement to create a new staggered-quark action (HISQ) that has greatly reduced one-loop taste-exchange errors, no tree-level order a^2 errors, and no tree-level order (am)^4 errors to leading order in the quark's velocity v/c. We demonstrate with simulations that the resulting action has taste-exchange interactions that are at least 3--4 times smaller than the widely used ASQTAD action. We show how to estimate errors due to taste exchange by comparing ASQTAD and HISQ simulations, and demonstrate with simulations that such errors are no more than 1% when HISQ is used for light quarks at lattice spacings of 1/10 fm or less. The suppression of (am)^4 errors also makes HISQ the most accurate discretization currently available for simulating c quarks. We demonstrate this in a new analysis of the psi-eta_c mass splitting using the HISQ action on lattices where a m_c=0.43 and 0.66, with full-QCD gluon configurations (from MILC). We obtain a result of~111(5) MeV which compares well with experiment. We discuss applications of this formalism to D physics and present our first high-precision results for D_s mesons.
  11/2006;
• Source

  Available from: arxiv.org

  Article: Accurate determinations of alpha(s) from realistic lattice QCD.

  Q Mason, H D Trottier, C T H Davies, K Foley, A Gray, G P Lepage, M Nobes, J Shigemitsu
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  ABSTRACT: We obtain a new value for the QCD coupling constant by combining lattice QCD simulations with experimental data for hadron masses. Our lattice analysis is the first to (1) include vacuum polarization effects from all three light-quark flavors (using MILC configurations), (2) include third-order terms in perturbation theory, (3) systematically estimate fourth and higher-order terms, (4) use an unambiguous lattice spacing, and (5) use an [symbol: see text](a2)-accurate QCD action. We use 28 different (but related) short-distance quantities to obtain alpha((5)/(MS))(M(Z)) = 0.1170(12).
  Physical Review Letters 08/2005; 95(5):052002. · 7.37 Impact Factor
• Source

  Available from: ArXiv

  Article: The Low-Lying Dirac Spectrum of Staggered Quarks

  E. Follana, A. Hart, C. T. H. Davies, Q. Mason
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  ABSTRACT: We investigate and clarify the role of topology and the issues surrounding the epsilon regime for staggered quarks. We study unimproved and improved staggered quark Dirac operators on quenched lattice QCD gluon backgrounds generated using a Symanzik-improved gluon action. For the improved Dirac operators we find a clear separation of the spectrum into would-be zero modes and others. The number of would-be zero modes depends on the topological charge as predicted by the continuum Index Theorem, and the expectation values of their chirality are large for the most improved actions (approx 0.7). The remaining modes have low chirality and show clear signs of clustering into quartets that become degenerate in the continuum limit. We demonstrate that the lattice spacing and volume dependence of the eigenvalues follow expectations. Furthermore, the non-zero modes follow the random matrix theory predictions for all topological charge sectors. The values of the chiral condensate extracted from fits to the theoretical distributions are consistent with each other, and with the results obtained from the total density of eigenvalues using the Banks-Casher relation. We conclude that staggered quarks respond correctly to QCD topology when both fermion and gauge actions are improved. Comment: 17 pages, a few typos corrected, part of one figure changed
  07/2005;
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  Available from: arxiv.org

  Article: First determination of the strange and light quark masses from full lattice QCD

  HPQCD collaboration, MILC collaboration, UKQCD collaboration, C. Aubin, C. Bernard, C. Davies, C. DeTar, Steven Gottlieb, A. Gray, E. Gregory, [......], U. Heller, J. Hetrick, G. Lepage, Q. Mason, J. Osborn, J. Shigemitsu, R. Sugar, D. Toussaint, H. Trottier, M. Wingate
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  ABSTRACT: We compute the strange quark mass $m_s$ and the average of the $u$ and $d$ quark masses $\hat m$ using full lattice QCD with three dynamical quarks combined with experimental values for the pion and kaon masses. The simulations have degenerate $u$ and $d$ quarks with masses $m_u=m_d\equiv \hat m$ as low as $m_s/8$, and two different values of the lattice spacing. The bare lattice quark masses obtained are converted to the $\msbar$ scheme using perturbation theory at $O(alpha_s)$. Our results are: $m_s^\msbar$(2 GeV) = 76(0)(3)(7)(0) MeV, $\hat m^\msbar$(2 GeV) = 2.8(0)(1)(3)(0) MeV and $m_s/\hat m$ = 27.4(1)(4)(0)(1), where the errors are from statistics, simulation, perturbation theory, and electromagnetic effects, respectively.
  06/2004;
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  Available from: arxiv.org

  Article: Improvement and Taste Symmetry Breaking for Staggered Quarks

  E. Follana, C Davies, A. Hart, P. Lepage, Q. Mason, H. Trottier
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  ABSTRACT: We compare several improved actions for staggered quarks. We study the effect of improvement on the taste changing interactions by calculating the splitting in the pion spectrum. We investigate the effect of the improvement on some topological properties. Comment: 3 pages, 3 figures, Lattice 2003 proceedings
  06/2004;
• Source

  Available from: arxiv.org

  Article: High-precision lattice QCD confronts experiment.

  C T H Davies, E Follana, A Gray, G P Lepage, Q Mason, M Nobes, J Shigemitsu, H D Trottier, M Wingate, C Aubin, [......], J E Hetrick, J Osborn, R Sugar, D Toussaint, M Di Pierro, A El-Khadra, A S Kronfeld, P B Mackenzie, D Menscher, J Simone
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  ABSTRACT: The recently developed Symanzik-improved staggered-quark discretization allows unquenched lattice-QCD simulations with much smaller (and more realistic) quark masses than previously possible. To test this formalism, we compare experiment with a variety of nonperturbative calculations in QCD drawn from a restricted set of "gold-plated" quantities. We find agreement to within statistical and systematic errors of 3% or less. We discuss the implications for phenomenology and, in particular, for heavy-quark physics.
  Physical Review Letters 02/2004; 92(2):022001. · 7.37 Impact Factor
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  Available from: arxiv.org

  Article: The determination of alpha_s from lattice QCD with 2+1 flavors of dynamical quarks

  C Davies, A. Gray, M. Alford, E. Follana, J. Hein, P. Lepage, Q. Mason, M. Nobes, J. Shigemit su, H. Trottier, M. Wingate
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  ABSTRACT: We describe the first lattice determination of the strong coupling constant with 3 flavors of dynamical quarks. The method follows previous analyses in using a perturbative expansion for the plaquette and Upsilon spectroscopy to set the scale. Using dynamical configurations from the MILC collaboration with 2+1 flavors of dynamical quarks we are able to avoid previous problems of having to extrapolate to 3 light flavors from 0 and 2. Our results agree with our previous work: alpha_s_MSbar(M_Z) = 0.121(3).
  10/2002;
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  Available from: ArXiv

  Article: The Upsilon Spectrum from Lattice QCD with 2+1 Flavors of Dynamical Quarks

  A. Gray, C Davies, M. Alford, E. Follana, J. Hein, G. P. Lepage, Q. Mason, M. Nobes, J. Shigemitsu, H. Trottier, M. Wingate
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  ABSTRACT: We describe the bottomonium spectrum obtained on the MILC configurations which incorporate 2+1 flavors of dynamical quarks. We compare to quenched and 2 flavor results also on MILC configurations. We show that the lattice spacing determination using different quantities shows clear signs of convergence with 2+1 flavors and give results for the leptonic width and hyperfine splitting, in the form of the ratio of the 1st excited state of the Upsilon to that of the ground state.
  10/2002;
• Source

  Available from: arxiv.org

  Article: On the strange quark mass with improved staggered quarks

  J. Hein, C Davies, G. P. Lepage, Q. Mason, H. Trottier
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  ABSTRACT: We present results on the sum of the masses of light and strange quark using improved staggered quarks. Our calculation uses 2+1 flavours of dynamical quarks. The effects of the dynamical quarks are clearly visible. Comment: Lattice2002(spectrum) Latex 3 pages, 2 figures
  09/2002;
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  Available from: arxiv.org

  Article: Second Order Perturbation Theory for Improved Gluon and Staggered Quark Actions

  M. Nobes, H. Trottier, G. P. Lepage, Q. Mason
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  ABSTRACT: We present the results of our perturbative calculations of the static quark potential, small Wilson loops, the static quark self energy, and the mean link in Landau gauge. These calculations are done for the one loop Symanzik improved gluon action, and the improved staggered quark action.
  11/2001;
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  Available from: arxiv.org

  Article: Mass renormalisation for improved staggered quarks

  J. Hein, Q. Mason, G. P. Lepage, H. Trottier
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  ABSTRACT: Improved staggered quark actions are designed to suppress flavour changing strong interactions. We discuss the perturbation theory for this type of actions and show the improvements to reduce the quark mass renormalisation compared to naive staggered quarks. The renormalisations are of similar size as for Wilson quarks.
  11/2001;
• Article: First determination of the strange and light quark masses from full lattice QCD

  C. Aubin, C. Bernard, C. T. H. Davies, C. DeTar, Steven A. Gottlieb, A. Gray, E. B. Gregory, J. Hein, U. M. Heller, J. E. Hetrick, G. P. Lepage, Q. Mason, J. Osborn, J. Shigemitsu, R. Sugar, D. Toussaint, H. Trottier, M. Wingate
  [show abstract] [hide abstract]
  ABSTRACT: We compute the strange quark mass ms and the average of the u and d quark masses m̂ using full lattice QCD with three dynamical quarks combined with the experimental values for the π and K masses. The simulations have degenerate u and d quarks with masses mu=md≡m̂ as low as ms/8, and two different values of the lattice spacing. The bare lattice quark masses obtained are converted to the MS̅ scheme using perturbation theory at O(αS). Our results are msMS̅ (2GeV)=76(0)(3)(7)(0)MeV, mMS̅ (2GeV)=2.8(0)(1)(3)(0) MeV, and ms/m̂=27.4(1)(4)(0)(1), where the errors are from statistics, simulation, perturbation theory, and electromagnetic effects, respectively.
  Phys. Rev. D. 70(3).
• Article: The determination of alpha _s from lattice QCD with 2+1 flavors of dynamical quarks

  C Davies, A. Gray, M. Alford, E. Follana, J. Hein, P. Lepage, Q. Mason, M. Nobes, J. Shigemitsu, H. Trottier, M. Wingate
  [show abstract] [hide abstract]
  ABSTRACT: We describe the first lattice determination of the strong coupling constant with 3 flavors of dynamical quarks. The method follows previous analyses in using a perturbative expansion for the plaquette and Upsilon spectroscopy to set the scale. Using dynamical configurations from the MILC collaboration with 2+1 flavors of dynamical quarks we are able to avoid previous problems of having to extrapolate to 3 light flavors from 0 and 2. Our result agrees with our previous work: alpha /sub theta //sup MS/(Mz) = 0.121(3).
• Article: Improvement and taste symmetry breaking for staggered quarks

  E. Follana, M. Alford, C Davies, P. Lepage, Q. Mason, J. Hein, H. Trottier
  [show abstract] [hide abstract]
  ABSTRACT: We compare several systematically improved actions for staggered quarks, suggested by a perturbative analysis. We study the effect of improvement on the taste changing interactions by calculating the splitting in the pion spectrum.