We report on the measurement of the static potential and the scale r_0 from HYP-smeared Wilson loops in two flavour QCD. We analyse the quark mass dependence of the potential and r_0 at three lattice spacings. We also compare the QCD static potential around distance r_0 with the static potential obtained from potential models.
Many exotic charmonium resonances have been identified recently in experiment, however their nature and properties are mostly unknown. Algorithmic and theoretical progress in lattice calculations has enabled reliable numerical investigation of the spectrum below the strong decay threshold, while the study of charmonium resonances remains an open challenge. The main difficulty to overcome is the presence of many open decay channels which are coupled together, resulting in a complex finite volume quantization condition. We report on our recent progress towards the determination of single-channel…
We report recent efforts by CLS to generate an ensemble with physical light- and strange-quark masses in a lattice volume of 192x96^3 at $β=3.55$ corresponding to a lattice spacing of 0.064 fm. This ensemble is being generated as part of the CLS 2+1 flavor effort with improved Wilson fermions. Our simulations currently cover 5 lattice spacings ranging from 0.039 fm to 0.086 fm at various pion masses along chiral trajectories with either the sum of the quark masses kept fixed, or with the strange-quark mass at the physical value. The current status of simulations is briefly reviewed, including …
We present the current status of our lattice QCD determination of the charm quark mass using $N_\mathrm{f}=2+1$ dynamical, non-perturbatively $\mathrm{O}(a)$ improved Wilson fermions. A subset of CLS ensembles with five different lattice spacings along the $\mathrm{Tr}[M_\mathrm{q}]=\text{const.}$ trajectory is used. For the computation of the correlation functions involving valence charm quark propagators, we employ distance preconditioning to gain the necessary precision. To stabilize the extrapolations to the physical point, we consider different definitions of the bare charm quark mass and…
We present measurements of a combination of the decay constants of the light pseudoscalar mesons and the gradient flow scale $t_0$, which allow to set the scale of the lattices generated by CLS with $2 + 1$ flavors of non-perturbatively improved Wilson fermions. Mistunings of the quark masses are corrected for by measuring the derivatives of observables with respect to the bare quark masses.
We determine the masses and pseudoscalar decay constants of D and D_s mesons employing lattice QCD with non-perturbatively O(a) improved Wilson quarks and a tree-level Symanzik-improved gauge action. Our analysis is based on the large-volume N_f=2+1 ensembles using open boundary conditions, generated within the CLS effort. The status of results presented here covers two lattice spacings, a ~ 0.0854 fm and a ~ 0.0644 fm, and pion masses varied from 420 to 200 MeV. We also report on our implementation of distance preconditioning for the calculation of heavy quark propagators and discuss the impa…
We report on the status of large volume simulations with 2+1 dynamical fermions which are being performed by the CLS initiative. The algorithmic details include: open boundary conditions, twisted mass reweighting and RHMC, whereas the main feature of the simulation strategy is the approach to the physical point along a trajectory of constant trace of the mass matrix. We comment on the practical side of the above issues using as examples some of the newly generated ensembles, which presently cover lattice spacings between 0.05 fm and 0.11 fm and pion masses between 150 MeV and 415 MeV.
We present preliminary results on the electromagnetic form factors and axial charge of the nucleon from ensembles generated by the CLS effort with $N_\mathrm{f}=2+1$ flavours of non-perturbatively $\mathrm{O}(a)$-improved Wilson fermions and open temporal boundary conditions. Systematic effects due to excited-state contamination are accounted for using both two-state fits and the method of summed operator insertions. This exploratory analysis demonstrates the viability of obtaining precision baryon observables with $N_\mathrm{f}=2+1$ flavours of Wilson fermions on fine lattices, aiming towards…
We report on the status of an ongoing effort by the RQCD and ALPHA Collaborations, aimed at determining leptonic decay constants of charmed mesons. Our analysis is based on large-volume ensembles generated within the CLS effort, employing N_f=2+1 non-perturbatively O(a) improved Wilson quarks, tree-level Symanzik-improved gauge action and open boundary conditions. The ensembles cover lattice spacings from a ~ 0.09 fm to a ~ 0.05 fm, with pion masses varied from 420 to 200 MeV. To extrapolate to the physical masses, we follow both the 2m_l+m_s=const. and the m_s=const. lines in parameter space.
We determine the non-perturbatively renormalized axial current for O($a$) improved lattice QCD with Wilson quarks. Our strategy is based on the chirally rotated Schrödinger functional and can be generalized to other finite (ratios of) renormalization constants which are traditionally obtained by imposing continuum chiral Ward identities as normalization conditions. Compared to the latter we achieve an error reduction up to one order of magnitude. Our results have already enabled the setting of the scale for the $N_{\rm f}=2+1$ CLS ensembles [1] and are thus an essential ingredient for the rece…
In this Letter, we provide a determination of the coupling constant in three-flavor quantum chromodynamics (QCD), $α^{\overline{\mathrm{MS}}}_s(μ)$, for $\overline{\mathrm{MS}}$ renormalization scales $μ\in (1,\,2)$ GeV. The computation uses gauge field configuration ensembles with $\mathcal{O}(a)$-improved Wilson-clover fermions generated by the Coordinated Lattice Simulations (CLS) consortium. Our approach is based on current-current correlation functions and has never been applied before in this context. We convert the results perturbatively to the QCD $Λ$-parameter and obtain $Λ_{\overline…
Based on CLS simulations with 2+1 flavors and open boundaries we present first results of the baryon spectrum. We report on the status of our effort related to these simulations and the chiral extrapolation to the physical point.
We present the current status of a non-perturbative lattice calculation of the moments of the pion and kaon distribution amplitudes by the RQCD collaboration. Our investigation is carried out using $N_f=2+1$ dynamical, non-perturbatively O(a)-improved Wilson fermions on the CLS ensembles with 5 different lattice spacings and pion masses down to the physical pion mass. A combined continuum and chiral extrapolation to the physical point is performed along two independent quark mass trajectories simultaneously. We employ momentum smearing in order to decrease the contamination by excited states a…
We consider three-flavor QCD and perform a determination of the low-energy coupling $\hat{g}_χ$ of SU(2) Heavy Meson Chiral Perturbation Theory. It is the $B^*Bπ$ coupling in the limit of static heavy and chiral light quarks and has not been determined with precision thus far. The calculation is performed on a large set of the $2+1$ flavor CLS ensembles with pion masses from 420 MeV down to 130 MeV. This allows us to significantly reduce the systematic uncertainty from the chiral extrapolation compared to previous works. Only a weak dependence on the lattice spacing is visible in our results.
We show recent results from the Mainz group using $N_f = 2 + 1$ CLS ensembles generated at the $SU(3)$ symmetric point. Temporal correlation functions using two-baryon interpolating operators are calculated with the distillation method. In addition to the spin-0 operators relevant for studying the $H$ dibaryon, we added spin-1 operators to our basis, thereby extending our results to other flavor sectors. These preliminary results show a finite-volume energy below the $ΛΛ$ threshold. Further calculations are necessary to establish whether the $H$ dibaryon is bound at the physical point.
We present lattice results for the non-perturbative Collins-Soper (CS) kernel, which describes the energy-dependence of transverse momentum-dependent parton distributions (TMDs). The CS kernel is extracted from the ratios of first Mellin moments of quasi-TMDs evaluated at different nucleon momenta.The analysis is done with dynamical $N_f=2+1$ clover fermions for the CLS ensemble H101 ($a=0.0854\,\mathrm{fm}$, $m_π=m_K=422\,\mathrm{MeV}$). The computed CS kernel is in good agreement with experimental extractions and previous lattice studies.
We determine quark mass dependent order $a$ improvement terms of the form $b_J am$ for non-singlet scalar, pseudoscalar, vector and axialvector currents, using correlators in coordinate space. We use a set of CLS ensembles comprising non-perturbatively improved Wilson Fermions and the tree-level Luescher-Weisz gauge action at $β=3.4,3.46,3.55$ and $β=3.7$, corresponding to lattice spacings $a$ ranging from $0.05$ fm to $0.09$ fm. We report the values of the $b_J$ improvement coefficients which are proportional to non-singlet quark mass combinations and also discuss the possibility of determini…
We report on progress applying the stochastic LapH method to estimate all-to-all propagators required in correlation functions of multi-hadron operators relevant for pion-pion scattering. Large-volume results for $I=2$ and $I=1$ pion-pion scattering phase shifts with good statistical precision are obtained from an $N_{\rm f} = 2+1$ anisotropic Wilson clover ensemble with $m_π = 240\mathrm{MeV}$. We also present a preliminary determination of the $I=1$ pion-pion scattering phase shift and timelike pion form factor on an isotropic $N_{\rm f}=2+1$ flavour ensemble generated by the Coordinated Lat…
We present an analysis of the pion-nucleon sigma term on the CLS ensembles with $N_f=2+1$ flavors of $\mathcal{O}(a)$-improved Wilson fermions. We perform a chiral interpolation based on ensembles with pion masses ranging from 130 MeV to roughly 350 MeV. The analysis covers four lattice spacings between $a\approx [0.05 \, \rm{fm}\ldots 0.09\, \rm{fm}]$, allowing for an estimate of systematics associated with lattice artefacts.
We report an ongoing analysis of nucleon-nucleon scattering based on finite-volume spectroscopy. The calculation is performed using the distillation method on eight lattice ensembles at the SU(3)-symmetric point with $m_π=m_K\approx 420$ MeV generated by CLS, covering a range of lattice spacings and volumes and previously used to study the $H$ dibaryon. We obtain nonzero signals for $S$, $P$, $D$, and $F$ waves as well as the mixing between spin-1 $S$ and $D$ waves. For $S$ waves, lattice artifacts are significant and tend to strengthen baryon-baryon interactions. In the deuteron and dineutron…
We compute various (generalized) isovector charges of the octet baryons. These include $g_A$, $g_T$ and $g_S$ as well as the unpolarized, polarized and transversity parton distribution function (PDF) momentum fractions $\langle x\rangle_{u^+-d^+}$, $\langle x\rangle_{Δu^--Δd^-}$ and $\langle x\rangle_{δu^+-δ^+}$. The simulations are carried out on a subset of the (isospin symmetric) $N_f=2+1$ flavour Coordinated Lattice Simulations (CLS) gauge ensembles with lattice spacings ranging from $a\approx 0.086\,$fm down to $a\approx 0.050\,$fm. First results on the breaking of flavour symmetry and th…
We present results for the isoscalar electromagnetic form factors of the nucleon computed on the Coordinated Lattice Simulations (CLS) ensembles with $N_\mathrm{f} = 2 + 1$ flavors of $\mathcal{O}(a)$-improved Wilson fermions and an $\mathcal{O}(a)$-improved conserved vector current. In order to estimate the excited-state contamination, we employ several source-sink separations and apply the summation method. For the computation of the quark-disconnected diagrams, a stochastic estimation based on the one-end trick is performed, in combination with a frequency-splitting technique and the hoppin…
We determine quark mass dependent order $a$ improvement terms of the form $b_Jam$ for non-singlet scalar, pseudoscalar, vector and axialvector currents using correlators in coordinate space on a set of CLS ensembles. These have been generated employing non-perturbatively improved Wilson Fermions and the tree-level Lüscher-Weisz gauge action at $β= 3.4, 3.46, 3.55$ and $3.7$, corresponding to lattice spacings ranging from $a \approx 0.085$ fm down to $0.05$ fm. In the $N_f=2+1$ flavour theory two types of improvement coefficients exist: $b_J$, proportional to non-singlet quark mass combinations…
We present preliminary results on the axial form factor $G_A(Q^2)$ and the induced pseudoscalar form factor $G_P(Q^2)$ of the nucleon. A systematic analysis of the excited-state contributions to form factors is performed on the CLS ensemble `N6' with $m_π= 340 \ \text{MeV}$ and lattice spacing $a \sim 0.05 \ \text{fm}$. The relevant three-point functions were computed with source-sink separations ranging from $t_s \sim 0.6 \ \text{fm}$ to $t_s \sim \ 1.4 \ \text{fm}$. We observe that the form factors suffer from non-trivial excited-state contributions at the source-sink separations available t…
Recently the LHCb experiment found evidence for the existence of two exotic resonances consisting of $c\bar{c}uud$ quarks. Among the possible interpretations is the hadro-charmonium model, in which charmonium is bound "within" a light hadron. We test this idea on CLS $N_f$=2+1 lattices using the static formulation for the heavy quarks. We find that the static potential is modified by the presence of a hadron such that it becomes more attractive. The effect is of the order of a few MeV.
We report about an ongoing lattice field theory project concerned with the investigation of heavy hybrid mesons. In particular we discuss our computation of the structure of hybrid static potential flux tubes in SU(2) lattice Yang-Mills theory, which is based on the squares of the chromoelectric and chromomagnetic field strength components. Our flux tube results for hybrid static potential quantum numbers $Σ_g^-$, $Σ_u^+$, $Σ_u^-$, $Π_g$, $Π_u$, $Δ_g$, $Δ_u$ are significantly different compared to the flux tube of the ordinary static potential.
We compute hybrid static potentials in $SU(3)$ lattice Yang-Mills theory at short quark-antiquark separations using four different small lattice spacings as small as $0.04\,\text{fm}$. The resulting static potentials are important, e.g. when studying heavy hybrid mesons in the Born-Oppenheimer approximation. We also discuss and exclude possible systematic errors from topological freezing, the finite lattice volume and glueball decays.
We present SU(3) lattice Yang-Mills data for hybrid static potentials from five ensembles with different small lattice spacings and the corresponding parametrizations for quark-antiquark separations $0.08\,\text{fm} \le r \le 1.12\,\text{fm}$. We remove lattice discretization errors at tree level of perturbation theory and partly at order $a^2$ as well as the $a$-dependent self energy. In particular the tree-level improvement of static potentials is discussed in detail and two methods are compared. The resulting parametrizations are expected to represent continuum limit results for hybrid stat…
We summarize our recent lattice gauge theory computation of the $Π_u$ and $Σ_u^-$ hybrid static potentials at small quark-antiquark separations. We provide parameterizations of the resulting lattice data points, which can be used for investigating masses and properties of heavy hybrid mesons in the Born-Oppenheimer approximation.
We present the analysis of isovector axial vector nucleon form factors on a set of $N_f=2+1$ CLS ensembles with $\mathcal O(a)$-improved Wilson fermions and Lüscher-Weisz gauge action. The set of ensembles covers a pion mass range of $130-353\,$MeV with lattice spacings between $0.05\,$fm and $0.09\,$fm. In particular, the set includes a $L/a=96$ ensemble at the physical pion mass. For the purpose of the form factor extraction, we employ both the summed operator insertion method (summation method) and explicit two-state fits in order to account for excited-state contributions to the nucleon co…
We compute the $Π_u$ and $Σ_u^-$ hybrid static potentials in SU(3) lattice gauge theory using four different lattice spacings ranging from $a = 0.040\,\text{fm}$ to $a = 0.093\,\text{fm}$. We provide lattice data points for quark-antiquark separations as small as $0.08\, \text{fm}$, where the $a$-dependent self-energy as well as lattice discretization errors at tree-level of perturbation theory and at leading order in $a^2$ have been removed. We also investigate and exclude possibly present systematic errors from topological freezing, due to the finite spatial lattice volume and from glueball …
We present preliminary results for the charm quark mass in the $N_f=4$ RGI scheme. These were obtained using $N_f=2+1$ CLS ensembles with $\mathcal{O}(a)$ non-perturbatively improved Wilson fermions. We employed five different lattice spacings, ranging down to $a\lesssim 0.04$ fm and realized approximately physical pion and kaon masses, with ensembles spread out along three different trajectories in the quark mass plane, enabling a thorough study of the dependence on the lattice spacing and the light and strange sea quark masses. We sketch our analysis strategy and find that the dominant error…
