Ron Horgan

Publications (6)0 Total impact

• Article: Precise Determinations of the Decay Constants of B and D mesons

  Heechang Na, Chris Monahan, Christine Davies, Eduardo Follana, Ron Horgan, Peter Lepage, Junko Shigemitsu
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  ABSTRACT: Recently we studied the B, Bs, D and Ds meson decay constants using various treatments for the heavy quark. For B mesons, we determined fB, fBs, and fBs/fB with NRQCD bottom quarks. We then combined the ratio fBs/fB and another very precise determination from HPQCD for fBs using heavy HISQ quarks, and extracted fB with 2% total errors. We also calculated fD, fDs, and fDs/fD using HISQ charm quarks. Here we review our results and briefly discuss their implications for the determination of the CKM matrix elements |Vcd| and |Vcs|.
  12/2012;
• Article: Matching lattice and continuum axial-vector and vector currents with NRQCD and HISQ quarks

  Christopher Monahan, Junko Shigemitsu, Ron Horgan
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  ABSTRACT: We match the continuum and lattice axial vector and vector currents at one loop in perturbation theory. For the heavy quarks we use the nonrelativistic QCD (NRQCD) action and for the light quarks the Highly Improved Staggered Quark (HISQ) action. We present results for both massless and massive HISQ quarks and as part of the matching procedure we include a discussion of the one loop HISQ renormalisation parameters.
  11/2012;
• Article: Matching heavy-light currents with NRQCD and HISQ quarks

  Christopher Monahan, Christine Davies, Ron Horgan, G. Peter Lepage, Heechang Na, Junko Shigemitsu
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  ABSTRACT: We calculate the one loop renormalisation parameters for the heavy-light axial-vector and vector currents using lattice perturbation theory. We use NonRelativistic QCD (NRQCD) heavy quarks and the Highly Improved Staggered Quark (HISQ) action for the light quarks. We present results for heavy-light currents with massless HISQ quarks and briefly discuss the extension to heavy-heavy currents with massive HISQ quarks.
  10/2012;
• Source

  Available from: ArXiv

  Article: The B and B_s Meson Decay Constants from Lattice QCD

  Heechang Na, Chris J. Monahan, Christine T. H. Davies, Ron Horgan, G. Peter Lepage, Junko Shigemitsu
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  ABSTRACT: We present a new determination of the B and B_s meson decay constants using NRQCD b-quarks, HISQ light and strange valence quarks and the MILC collaboration N_f=2+1 lattices. The new calculations improve on HPQCD's earlier work with NRQCD b-quarks by replacing AsqTad with HISQ valence quarks, by including a more chiral MILC fine ensemble in the analysis, and by employing better tuned quark masses and overall scale. We find f_B = 0.191(9)GeV, f_{B_s} = 0.228(10)GeV and f_{B_s}/f_B = 1.188(18). Combining the new value for f_{B_s}/f_B with a recent very precise determination of the B_s meson decay constant based on HISQ b-quarks, f_{B_s} = 0.225(4)GeV, leads to f_B = 0.189(4)GeV. With errors of just 2.1% this represents the most precise f_B available today.
  02/2012;
• Source

  Available from: ArXiv

  Article: Studies of B and B_s Meson Leptonic Decays with NRQCD Bottom and HISQ Light/Strange Quarks

  Junko Shigemitsu, Heechang Na, Christine Davies, Ron Horgan, Chris Monahan, Peter Lepage
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  ABSTRACT: We present a progress report on new calculations of B and B_s meson decay constants employing NRQCD heavy and HISQ light valence quarks and using MILC N_f = 2+1 AsqTad lattices. Bare quark masses have been retuned in accord with HPQCD's new r_1 scale. We find significant reductions in discretization effects compared to previous calculations with AsqTad light valence quarks. Matching of the NRQCD/HISQ heavy-light axial vector current is carried out at one-loop order including all relevant dimension 4 current corrections.
  10/2011;
• Source

  Available from: sissa.it

  Article: Progress on Perturbative Matching Calculations for the Charm Quark Mass using the HISQ Action

  Emel Dalgic, Kit Wong, Christine Davies, Eduardo Follana, Alistair Hart, Ron Horgan, Peter Lepage, Quentin Mason, Junko Shigemitsu, Howard Trottier, Jackson Wu
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  ABSTRACT: The highly-improved staggered quark (HISQ) action is the most accurate discretization scheme to date for the charm quark. Here we report on the progress of perturbative matching for the quark mass using the HISQ action. The matching is done through O(α 2 s) using a combination of Monte Carlo simulations at weak coupling and diagrammatic perturbation theory. When combined with on-going simulation efforts using the HISQ action, a determination of the charm quark mass to a few percent accuracy can be achieved. Of particular interest will be a comparison with the recent sum rule determination of the charm mass due to Kühn et al. [1].
  PoS. 01/2007;