H. Trottier

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

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 O(a{sup 2})-accurate QCD action. We use 28 different (but related) short-distance quantities to obtain {alpha}{sub MS}{sup (5)}(M{sub Z})=0.1170(12)

Direct determination of the strange and light quark condensates from full lattice QCD

We determine the strange quark condensate from lattice QCD for the first time and compare its value to that of the light quark and chiral condensates. The results come from a direct calculation of the expectation value of the trace of the quark propagator followed by subtraction of the appropriate perturbative contribution, derived here, to convert the non-normal-ordered mψ ψ to the MS scheme at a fixed scale. This is then a well-defined physical “nonperturbative” condensate that can be used in the operator product expansion of current-current correlators. The perturbative subtraction is calculated through O(αs) and estimates of higher order terms are included through fitting results at multiple lattice spacing values. The gluon field configurations used are “second generation” ensembles from the MILC collaboration that include 2+1+1 flavors of sea quarks implemented with the highly improved staggered quark action and including u/d sea quarks down to physical masses. Our results are ⟨s s⟩MS (2u2009u2009GeV)=-(290(15)u2009u2009MeV)3, ⟨l l⟩MS (2u2009u2009GeV)=-(283(2)u2009u2009MeV)3, where l is a light quark with mass equal to the average of the u and d quarks. The strange to light quark condensate ratio is 1.08(16). The light quark condensate is significantly larger than the chiral condensate in line with expectations from chiral analyses. We discuss the implications of these results for other calculations.

String breaking by dynamical fermions in three-dimensional lattice QCD

The first observation is made of hadronic string breaking due to dynamical fermions in zero temperature lattice QCD. The simulations are done for SU(2) color in three dimensions, with two flavors of staggered fermions. The results have clear implications for the large scale simulations that are being done to search (so far, without success) for string breaking in four-dimensional QCD. In particular, string breaking is readily observed using only Wilson loops to excite a static quark-antiquark pair. Improved actions on coarse lattices are used, providing an extremely efficient means to access the quark separations and propagation times at which string breaking occurs.

The Determination of alpha(s) from lattice QCD with 2+1 flavors of dynamical quarks

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).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).

Highly improved naive and staggered fermions

We present a new action for highly improved staggered fermions. We show that perturbative calculations for the new action are well-behaved where those of the conventional staggered action are badly behaved. We discuss the effects of the new terms in controlling flavor mixing, and discuss the design of operators for the action.

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

Emel Dalgic ab, Kit Wongc, Christine Daviesc, Eduardo Follanad,Alistair Harte,Ron Horgan f , Peter Lepageg, Quentin Mason f , Junko Shigemitsud, Howard Trottiera and Jackson Wub aSimon Fraser University, Burnaby BC, Canada V5A 1S6 bTRIUMF, Vancouver BC, Canada V6T 2A3 cUniversity of Glasgow, Glasgow, UK G12 8QQ dThe Ohio State University, Columbus OH, USA 43210 eUniversity of Edinburgh, Edinburgh, UK EH9 3JZ f University of Cambridge, Cambridge, UK CB3 0HE gCornell University, Ithaca NY, USA 14853

The Upsilon spectrum from lattice QCD with (2+1) flavors of dynamical quarks

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.

Update: Accurate determinations ofαsfrom realistic lattice QCD

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).

B and D meson semileptonic decays in three-flavor lattice QCD

P.B. Mackenzie∗,a, C. Aubinc,d , C. Bernardd , C. DeTare, M. Di Pierro f , Steven Gottliebh, E. Gregory j, U.M. Hellerk, J.E. Hetrickl, A.X. El-Khadram, A.S. Kronfelda, L. Levkovah, F. Marescae, D. Menscherm, M. Nobesn,o, M. Okamotoa, M.B. Oktayq, J. Osborne, D. Renner j, J.N. Simonea, R. Sugarp, D. Toussaint j, H.D. Trottiero E-mail: mackenzie@fnal.gov aFermi National Accelerator Laboratory, Batavia, Illinois 60510, USA cPhysics Department, Columbia University, New York, New York, USA dDepartment of Physics, Washington University, St. Louis, Missouri 63130, USA ePhysics Department, University of Utah, Salt Lake City, Utah 84112, USA f School of Computer Science, Telecommunications and Information Systems, DePaul University,

Accurate Determinations ofαsfrom Realistic Lattice QCD

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 O(a{sup 2})-accurate QCD action. We use 28 different (but related) short-distance quantities to obtain {alpha}{sub MS}{sup (5)}(M{sub Z})=0.1170(12)