showing 8 related works from this author
Study of the anomalous magnetic moment of the muon computed from the Adler function
2014
We compute the Adler function on the lattice from vacuum polarization data with twisted boundary conditions using numerical derivatives. The study is based on CLS ensembles with two flavours of $O(a)$ improved Wilson fermions. We extrapolate the lattice data for the Adler function to the continuum limit and to the physical pion mass and analyze its dependence on the momentum transfer. We discuss the application of this method to the extraction of the $u,d$ contribution to $a_\mu^{\mathrm{HLO}}$.
Lattice Determination of the Anomalous Magnetic Moment of the Muon
2011
We compute the leading hadronic contribution to the anomalous magnetic moment of the muon a_mu^HLO using two dynamical flavours of non-perturbatively O(a) improved Wilson fermions. By applying partially twisted boundary conditions we are able to improve the momentum resolution of the vacuum polarisation, an important ingredient for the determination of the leading hadronic contribution. We check systematic uncertainties by studying several ensembles, which allows us to discuss finite size effects and lattice artefacts. The chiral behavior of a_mu^HLO turns out to be non-trivial, especially for small pion masses.
Excited state systematics in extracting nucleon electromagnetic form factors
2012
We present updated preliminary results for the nucleon electromagnetic form factors for non-perturbatively $\mathcal{O}(a)$ improved Wilson fermions in $N_f=2$ QCD measured on the CLS ensembles. The use of the summed operator insertion method allows us to suppress the influence of excited states in our measurements. A study of the effect that excited state contaminations have on the $Q^2$ dependence of the extracted nucleon form factors may then be made through comparisons of the summation method to standard plateau fits, as well as to excited state fits.
The leading disconnected contribution to the anomalous magnetic moment of the muon
2014
The hadronic vacuum polarization can be determined from the vector correlator in a mixed time-momentum representation. We explicitly calculate the disconnected contribution to the vector correlator, both in the $N_f = 2$ theory and with an additional quenched strange quark, using non-perturbatively $O(a)$-improved Wilson fermions. All-to-all propagators are computed using stochastic sources and a generalized hopping parameter expansion. Combining the result with the dominant connected contribution, we are able to estimate an upper bound for the systematic error that arises from neglecting the disconnected contribution in the determination of $(g-2)_\mu$.
The hadronic vacuum polarization function with O(a)-improved Wilson fermions - an update
2016
We present an update of our lattice QCD study of the vacuum polarization function using O$(a)$-improved $N_ {\rm f} =2$ Wilson fermions with increased statistics and a large set of momenta. The resulting points are highly correlated and thus require a correlated fitting procedure. We employ an extended frequentist method to estimate the systematic uncertainties due to the momentum dependence and to the continuum and chiral extrapolations. We present preliminary results of the leading order hadronic contribution of the anomalous magnetic moment of the muon $\left(a_\mu^{\mathrm{HLO}}\right)$ at the physical point for $u,d,s$ and $c$ valence quarks.
Adler function and hadronic vacuum polarization from lattice vector correlators in the time-momentum representation
2014
We study a representation of the hadronic vacuum polarization based on the time-momentum representation of the vector correlator. This representation suggests a way to compute the hadronic vacuum polarization and the associated Adler function for any value of virtuality, irrespective of the flavor structure of the current. We present results on both of these phenomenologically important functions, derived from local-conserved two-point lattice vector correlation functions, computed on a subset of light two-flavor ensembles made available to us through the CLS effort.
Getting covariantly smeared sources into better shape
2014
The use of covariantly smeared sources in hadronic correlators is a common method of improving the projection onto the ground state. Studying the dependence of the shape of such sources on the gauge field background, we find that localized fluxes of magnetic field can strongly distort the sources. This results in a reduction of the smearing radii that can be reached by iterative smearing prescriptions, in particular as the continuum limit is approached. As a remedy, we propose a novel covariant smearing procedure (“free-form smearing”) enabling the creation of arbitrarily shaped sources, including in particular Gaussians of arbitrary radius, as well as shapes with nodes, such as hydrogenic …
Fitting strategies to extract the axial charge of the nucleon from lattice QCD
2014
We report on a comparison of several fit methods used for the extraction of the nucleon axial charge gA from lattice QCD with two dynamical flavours of O(a) improved Wilson quarks. We use plateau fits, summed operator insertions (the summation method) and a new “midpoint” method to investigate contributions from excited states that affect the determination of gA. We also present a method to perform correlated fits when the standard estimator for the inverse of the covariance matrix becomes unstable.