We present first results on the $\rho$ resonance parameters obtained with
$N_f=2+1+1$ Wilson twisted mass fermions at maximal twist. Using ensembles of
the ETM collaboration, we provide results for ...two values of the lattice spacing
and a range of pion mass values.
We present results for the isospin-0 $\pi\pi$ s-wave scattering length
calculated in twisted mass lattice QCD. We use three $N_f = 2$ ensembles with
unitary pion mass at its physical value, 240~MeV ...and 330~MeV respectively. We
also use a large set of $N_f = 2 + 1 +1$ ensembles with unitary pion masses
varying in the range of 230~MeV - 510~MeV at three different values of the
lattice spacing. A mixed action approach with the Osterwalder-Seiler action in
the valence sector is adopted to circumvent the complications arising from
isospin symmetry breaking of the twisted mass quark action. Due to the
relatively large lattice artefacts in the $N_f = 2 + 1 +1$ ensembles, we do not
present the scattering lengths for these ensembles. Instead, taking the
advantage of the many different pion masses of these ensembles, we
qualitatively discuss the pion mass dependence of the scattering properties of
this channel based on the results from the $N_f = 2 + 1 +1$ ensembles. The
scattering length is computed for the $N_f = 2$ ensembles and the chiral
extrapolation is performed. At the physical pion mass, our result $M_\pi
a^\mathrm{I=0}_0 = 0.198(9)(6)$ agrees reasonably well with various
experimental measurements and theoretical predictions.
Phys. Rev. D 96, 054516 (2017) We present results for the isospin-0 $\pi\pi$ s-wave scattering length
calculated with Osterwalder-Seiler valence quarks on Wilson twisted mass gauge
configurations. We ...use three $N_f = 2$ ensembles with unitary (valence) pion
mass at its physical value (250$\sim$MeV), at 240$\sim$MeV (320$\sim$MeV) and
at 330$\sim$MeV (400$\sim$MeV), respectively. By using the stochastic Laplacian
Heaviside quark smearing method, all quark propagation diagrams contributing to
the isospin-0 $\pi\pi$ correlation function are computed with sufficient
precision. The chiral extrapolation is performed to obtain the scattering
length at the physical pion mass. Our result $M_\pi a^\mathrm{I=0}_0 =
0.198(9)(6)$ agrees reasonably well with various experimental measurements and
theoretical predictions. Since we only use one lattice spacing, certain
systematics uncertainties, especially those arising from unitary breaking, are
not controlled in our result.
We present results for the $I=2$ $\pi\pi$ scattering length using $N_f=2+1+1$
twisted mass lattice QCD for three values of the lattice spacing and a range of
pion mass values. Due to the use of ...Laplacian Heaviside smearing our
statistical errors are reduced compared to previous lattice studies. A detailed
investigation of systematic effects such as discretisation effects, volume
effects, and pollution of excited and thermal states is performed. After
extrapolation to the physical point using chiral perturbation theory at NLO we
obtain $M_\pi a_0=-0.0442(2)_\mathrm{stat}(^{+4}_{-0})_\mathrm{sys}$.
We present results for the nucleon electromagnetic form factors, including the momentum transfer dependence and derived quantities (charge radii and magnetic moment). The analysis is performed using ...O(a) improved Wilson fermions in Nf=2 QCD measured on the CLS ensembles. Particular focus is placed on a systematic evaluation of the influence of excited states in three-point correlation functions, which lead to a biased evaluation, if not accounted for correctly. We argue that the use of summed operator insertions and fit ans\"atze including excited states allow us to suppress and control this effect. We employ a novel method to perform joint chiral and continuum extrapolations, by fitting the form factors directly to the expressions of covariant baryonic chiral effective field theory. The final results for the charge radii and magnetic moment from our lattice calculations include, for the first time, a full error budget. We find that our estimates are compatible with experimental results within their overall uncertainties.
We present first results on the \(\rho\) resonance parameters obtained with \(N_f=2+1+1\) Wilson twisted mass fermions at maximal twist. Using ensembles of the ETM collaboration, we provide results ...for two values of the lattice spacing and a range of pion mass values.
We present results for the isospin-0 \(\pi\pi\) s-wave scattering length calculated with Osterwalder-Seiler valence quarks on Wilson twisted mass gauge configurations. We use three \(N_f = 2\) ...ensembles with unitary (valence) pion mass at its physical value (250\(\sim\)MeV), at 240\(\sim\)MeV (320\(\sim\)MeV) and at 330\(\sim\)MeV (400\(\sim\)MeV), respectively. By using the stochastic Laplacian Heaviside quark smearing method, all quark propagation diagrams contributing to the isospin-0 \(\pi\pi\) correlation function are computed with sufficient precision. The chiral extrapolation is performed to obtain the scattering length at the physical pion mass. Our result \(M_\pi a^\mathrm{I=0}_0 = 0.198(9)(6)\) agrees reasonably well with various experimental measurements and theoretical predictions. Since we only use one lattice spacing, certain systematics uncertainties, especially those arising from unitary breaking, are not controlled in our result.
Phys. Rev. D 95, 094515 (2017) We present physics results from simulations of QCD using $N_f = 2$ dynamical
Wilson twisted mass fermions at the physical value of the pion mass. These
simulations were ...enabled by the addition of the clover term to the twisted mass
quark action. We show evidence that compared to previous simulations without
this term, the pion mass splitting due to isospin breaking is almost completely
eliminated. Using this new action, we compute the masses and decay constants of
pseudoscalar mesons involving the dynamical up and down as well as valence
strange and charm quarks at one value of the lattice spacing, $a \approx 0.09$
fm. Further, we determine renormalized quark masses as well as their
scale-independent ratios, in excellent agreement with other lattice
determinations in the continuum limit. In the baryon sector, we show that the
nucleon mass is compatible with its physical value and that the masses of the
$\Delta$ baryons do not show any sign of isospin breaking. Finally, we compute
the electron, muon and tau lepton anomalous magnetic moments and show the
results to be consistent with extrapolations of older ETMC data to the
continuum and physical pion mass limits. We mostly find remarkably good
agreement with phenomenology, even though we cannot take the continuum and
thermodynamic limits.
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