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F. Bahr,
F. Bernardoni,
B. Blossier,
J. Bulava,
M. Della Morte,
P. Fritzsch,
N. Garron,
A. Gérardin,
J. Heitger,
G. von Hippel,
A. Ramos,
H. Simma, R. Sommer
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ABSTRACT: The 2012 PDG reports a tension at the level of $3 \sigma$ between two
exclusive determinations of $|V_{ub}|$. They are obtained by combining the
experimental branching ratios of $B \to \tau \nu$ and $B \to \pi l \nu$
(respectively) with a theoretical computation of the hadronic matrix elements
$\fB$ and the $B \to \pi$ form factor $f_+(q^2)$. To understand the tension,
improved precision and a careful analysis of the systematics involved are
necessary. We report the results of the ALPHA collaboration for $\fB$ from the
lattice with 2 flavors of $O(a)$ improved Wilson fermions. We employ HQET,
including $1/m_b$ corrections, with pion masses ranging down to $\approx$ 190
MeV. Renormalization and matching were performed non-perturbatively, and three
lattice spacings reaching $a^{-1}\approx 4.1$ GeV are used in the continuum
extrapolation. We also present progress towards a computation of $f_+(q^2)$, to
directly compare two independent exclusive determinations of $|V_{ub}|$ with
each other and with inclusive determinations. Additionally, we report on
preliminary results for $\fBq{s}$, needed for the analysis of $B_s \to
\mu^+\mu^-$.}
11/2012;
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F. Bernardoni,
B. Blossier,
J. Bulava,
M. Della Morte,
P. Fritzsch,
N. Garron,
A. Gérardin,
J. Heitger,
G. von Hippel,
H. Simma, R. Sommer
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ABSTRACT: We present our analysis of B physics quantities using non-perturbatively
matched Heavy Quark Effective Theory (HQET) in Nf= 2 lattice QCD on the CLS
ensembles. Using all-to-all propagators, HYP-smeared static quarks, and the
Generalized Eigenvalue Problem (GEVP) approach with a conservative plateau
selection procedure, we are able to systematically control all sources of
error. With significantly increased statistics compared to last year, our
preliminary results are mb (mb) = 4.22(10)(4)z GeV for the MS b-quark mass, and
fB = 193(9)stat (4)_\chi MeV and fBs = 219(12)stat MeV for the B-meson decay
constants.
10/2012;
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ABSTRACT: We analyze the systematic errors made when using the generalized eigenvalue problem to extract energies and matrix elements in lattice gauge theory. Effective theories such as HQET are also discussed. Numerical results are shown for the extraction of ground-state and excited B-meson masses and the ground-state decay constant in the static approximation. Comment: 8 pages, 3 postscript figures; talk presented at the XXVI Symposium on Lattice Field Theory, Williamsburg, Virginia, USA, July 14-19 2008
08/2008;
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ABSTRACT: We discuss some large effects of dynamical fermions. One is a cutoff effect, others concern the contribution of multi-pion states to correlation functions and are expected to survive the continuum limit. We then turn to the preparation for simulations at small lattice spacings which we are planning down to around a=0.04fm in order to understand the size of O(a^2)-effects of the standard O(a)-improved theory. The dependence of the lattice spacing on the bare coupling is determined through the Schr"odinger functional renormalized coupling.
11/2007;
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ABSTRACT: We perform the non-perturbative (quenched) renormalization of the chromo-magnetic operator in Heavy Quark Effective Theory and its three-loop matching to QCD. At order 1/m of the expansion, the operator is responsible for the mass splitting between the pseudoscalar and vector B-mesons. These new computed factors are affected by an uncertainty negligible in comparison to the known bare matrix element of the operator between B-states. Furthermore, they push the quenched determination of the spin splitting for the Bs-meson much closer to its experimental value than the previous perturbatively renormalized computations. The renormalization factor for three commonly used heavy quark actions and the Wilson gauge action and useful parametrizations of the matching coefficient are provided.
11/2007;
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R. Sommer
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ABSTRACT: Aus Beobachtungen von BAV-Mitgliedern in dem Zeitraum 1950 bis 1955 werden instantane Lichtwechselelemente des Algol-Sternes SV Cam hergeleitet und mit den lteren Beobachtungen seit 1897 verglichen. Es ergibt sich eine Sinusschwankung der Periode im Verlauf von 57 Jahren.
Astronomische Nachrichten 03/2006; 283(4):155 - 158. · 1.01 Impact Factor
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ABSTRACT: We discuss the correlators in lattice HQET that are needed to go beyond the static theory. Based on our implementation in the Schr\"odinger functional we focus on their signal-to-noise ratios and check that a reasonable statistical precision can be reached in quantities like $f_{B_s}$ and $M_{B^\star}-M_B$. Comment: 3 pages, Lattice2004(heavy), v2: corrected definition of X^{kin/spin}
09/2004;
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ABSTRACT: We present an algorithmic study for the simulation of two massless flavors of O(a) improved Wilson quarks with Schroedinger functional boundary conditions. The algorithm used is Hybrid Monte Carlo with two pseudo-fermion fields as proposed by M. Hasenbusch. A gain in CPU cost of a factor two is reached when compared to one pseudo-fermion field due to the larger possible step-size. This study is integrated in the ALPHA project for the computation of the running of the renormalized quark mass. We include an update on these physics results. Comment: 3 pages, 3 figures, Lattice2003(machine)
09/2003;
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ABSTRACT: We present a computation of the decay constant f_Bs in quenched QCD. Our strategy is to combine new precise data from the static approximation with an interpolation of the decay constant around the charm quark mass region. This computation is the first step in demonstrating the feasability of a strategy for f_B in full QCD. The continuum limits in the static theory and at finite mass are taken separately and will be further improved. Comment: Lattice2003(heavy), 3 pages, 2 figures
09/2003;
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ABSTRACT: We introduce an alternative discretization for static quarks on the lattice retaining the O(a) improvement properties of the Eichten-Hill action. In this formulation, statistical fluctuations are reduced by a factor which grows exponentially with Euclidean time, x_0. For the first time, B-meson correlation functions are computed with good statistical precision in the static approximation for x_0>1 fm. At lattice spacings a \approx 0.1 fm, a \approx 0.08 fm and a \approx 0.07 fm the B_s-meson decay constant is determined in static and quenched approximations. A correction due to the finite mass of the b-quark is estimated by combining these static results with a recent determination of F_Ds.
08/2003;
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ABSTRACT: We give here the contents pages for the Proceedings of the Lattice 2001 conference (19th International Symposium on Lattice Field Theory) that took place in August 2001 in Berlin, Germany. The contents are in HTML form with clickable links to the papers that exist on the arXiv, mostly in hep-lat. Corrections and comments should be sent to bunk@physik.hu-berlin.de. Comment: HTML file with links to Lattice 2001 papers. Authors listed are proceedings editors
03/2002;
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ABSTRACT: We study the potential of a static quark anti-quark pair in the confinement ``phase'' of the SU(2) Higgs model. Around separation r_b, the confining string of the gauge field breaks by formation of a dynamical pair of light quarks. The ground state and first excited state static potentials are determined by a variational technique from a matrix correlation in which suitably smeared gauge and Higgs fields enter. Our results at beta=2.4 clearly show string breaking (r_b ~ 1.9r_0). The investigation of properly defined overlaps confirms the interpretation of string breaking as a level crossing phenomenon between string-type and meson-type states. We study the scaling properties of the static potentials along a line of constant physics, varying the lattice spacing by a factor of 2. Our results show compatibility with scaling within tiny errors. Comment: 21 pages, 9 figures
05/2000;
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ABSTRACT: We present results for the reference scale r_0 in SU(3) Lattice Gauge Theory for beta = 6/g_0^2 in the range 5.7 <= beta <= 6.57. The high relative accuracy of 0.3-0.6% in r_0/a was achieved through good statistics, the application of a multi-hit procedure and a variational approach in the computation of Wilson loops. A precise definition of the force used to extract r_0 has been used throughout the calculation which guarantees that r_0/a is a smooth function of the bare coupling and that subsequent continuum extrapolations are possible. The results are applied to the continuum extrapolations of the energy gap Delta in the static quark potential and the scale L_max/r_0 used in the calculation of the running coupling constant.
07/1998;
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ABSTRACT: A previously introduced multi-boson technique for the simulation of QCD with dynamical quarks is described and some results of first test runs on a $6^3\times12$ lattice with Wilson quarks and gauge group SU(2) are reported. Comment: 7 pages, postscript file (166 KB)
11/1994;
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ABSTRACT: We show that the renormalization factor relating the renormalization group invariant quark masses to the bare quark masses computed in lattice QCD can be determined non-perturbatively. The calculation is based on an extension of a finite-size technique previously employed to compute the running coupling in quenched QCD. As a by-product we obtain the Λ-parameter in this theory with completely controlled errors.
Nuclear Physics B - Proceedings Supplements.
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ABSTRACT: We present and discuss results for cutoff effects in the PCAC masses and the mass dependence of r0 for full QCD and various fermion actions. Our discussion of how one computes mass dependences - here of r0 - is also relevant for comparisons with chiral perturbation theory.
Nuclear Physics B - Proceedings Supplements.
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ABSTRACT: We consider QCD with one massless quark and one heavy quark in a finite volume of linear extent L_0 ~ 0.2 fm. In this situation, HQET represents an expansion in terms of 1/z=1/(m L_0), which we test by a non-perturbative computation of quenched current matrix elements and energies, taking the continuum limit of lattice results. These are seen to approach the corresponding renormalization group invariant matrix elements of the static effective theory as the quark mass becomes large. We are able to obtain estimates of the size of the 1/m-corrections to the static theory, which are also of practical relevance in our recent strategy to implement HQET non-perturbatively by matching to QCD in a finite volume.
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JHEP 1006(2010),002.
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ABSTRACT: The ideas underlying a recent computation of the running coupling in the SU(2) gauge theory are discussed and a summary of the results obtained is given.
Nuclear Physics B - Proceedings Supplements.
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JHEP 1005(2010),074.
