We present results for masses of excited mesons from dynamical clover-Wilson lattices provided by the CP-PACS collaboration at pion masses down to 500 MeV. Our analysis of the data is based on using a matrix of correlators from various source and sink operators. The spectroscopy results are discussed and compared to experimental values.
Chiral perturbation theory for eigenvalue distributions, and equivalently random matrix theory, has recently been extended to include lattice effects for Wilson fermions. We test the predictions by comparison to eigenvalue distributions of the Hermitian Wilson-Dirac operator from pure gauge (quenched) ensembles. We show that the lattice effects are diminished when using clover improvement for the Dirac operator. We demonstrate that the leading Wilson low-energy constants associated with Wilson (clover) fermions can be determined using spectral information of the respective Dirac operator at fi…
We calculate the Sheikholeslami-Wohlert coefficient of the O(a) improvement term for Wilson fermions in any representation of the gauge group SU(N) perturbatively at the one-loop level. The result applies to QCD with adjoint quarks and to N=1 supersymmetric Yang-Mills theory on the lattice.
We present a status report of our calculation of the electromagnetic form factor of the pion on the PACS-CS gauge field configurations generated using Iwasaki gauge action and Wilson-clover quark action for 2 + 1 flavors of light dynamical quarks. The technique of twiseted boundary conditon is employed to explore the form factor for small momentum transfer. The $q^2$ behavior of the form factor and its light quark mass dependence is examined.
We present an update of the finite temperature phase structure analysis for three flavor QCD. In the study the Iwasaki gauge action and non-perturvatively O($a$) improved Wilson-Clover fermion action are employed. We discuss finite size scaling analysis including mixings of magnetization-like and energy-like observables. Preliminary results are shown of the continuum limit of the critical point using newly generated data at Nt=8,10, including estimates of the critical pseudo-scalar meson mass and critical temperature.
We present results for excited meson spectra from $N_f=2$ clover-Wilson configurations provided by the CP-PACS Collaboration. In our study we investigate both low and high spin mesons. For spin-0 and spin-1 mesons, we are especially interested in the excited states. To access these states we construct several different interpolators from quark sources of different spatial smearings and calculate a matrix of correlators. For this matrix we then solve a generalized eigenvalue problem. For spin-2 and spin-3, we extract only the lowest lying states.
We present a preliminary study of the pion, kaon and D-meson masses and decay constants in isosymmetric QCD, as well as a preliminary result for the light-quark renormalized mass. The analysis is based on the gauge ensembles produced by ETMC with $N_f=2+1+1$ flavours of Wilson-clover twisted mass quarks, spanning a range of lattice spacings from $\sim0.10$ to $0.07$ fm and include configurations at the physical pion point on lattices with linear size up to $L~\sim~5.6$~fm
We present results on the nucleon electromagnetic form factors from Lattice QCD at momentum transfer up to about $12$~GeV$^2$. We analyze two gauge ensembles with the Wilson-clover fermion action, a lattice spacing of $a\approx 0.09$~fm and pion masses $m_π\approx 170$~MeV and $m_π\approx 280$~MeV. In our analysis we employ momentum smearing as well as a set of techniques to investigate excited state effects. Good agreement with experiment and phenomenology is found for the ratios $G_E/G_M$ and $F_2/F_1$, whereas discrepancies are observed for the individual form factors $F_1$ and $F_2$. We di…
We report our study on the critical endpoint of the finite temperature phase transition in 4-flavor QCD with Wilson-Clover fermions. Using the kurtosis intersection method, we determined the critical endpoint on lattices with $N_t$ = 4, 6 and 8. Our continuum extrapolated results show that the pseudo-scalar meson mass at the critical endpoint, $m_\mathrm{PS,E}$, for 4-flavor is clearly larger than that for 3-flavor. We also compared our results to those with staggered fermions and found that $m_\mathrm{PS,E}/T_E$ for 4-flavor with Wilson fermions might remain finite even in the continuum limit…
Using an ensemble of 535 gauge configurations (on the $24^4 \times 48 $ lattice with $ a \simeq 0.06 $~fm and $ M_π \simeq 260 $~MeV) which are generated by hybrid Monte Carlo (HMC) simulation of $N_f=2$ lattice QCD with the optimal domain-wall quark, we compute the index of the overlap-Dirac operator, and also measure the clover topological charge in the Wilson flow, $Q_{\text{clover}}(t) $, by integrating the flow equation from $ t = 0 $ to $ t = 128 $ with $δt = 0.01 $. We observe that $Q_{\text{clover}}(t) $ of each configuration converges to a value close to an integer, and its nearest in…
The QCD phase diagram is studied in the lattice QCD simulation with the imaginary chemical potential approach. We employ a clover-improved Wilson fermion action of two-flavors and a renormalization-group improved gauge action, and perform the simulation at an intermediate quark mass on a $8^3\times 4$ lattice. The QCD phase diagram in the imaginary chemical potential $μ_I$ region is investigated by performing the simulation for more than 150 points on the $(β,μ_I)$ plane. We find that the Roberge-Weiss phase transition at $μ_I/T=π/3$ is first order and its endpoint is second order, which are i…
We investigate the phase structure of 3-flavor QCD in the presence of finite quark chemical potential by using Wilson-Clover fermions. To deal with the complex action with finite density, we adopt the phase reweighting method. In order to survey a wide parameter region, we employ the multi-parameter reweighting method as well as the multi-ensemble reweighting method. Especially, we focus on locating the critical end point that characterizes the phase structure. It is estimated by the kurtosis intersection method for the quark condensate. For Wilson-type fermions, the correspondence between bar…
We present a determination of the gradient flow scales $w_0$, $\sqrt{t_0}$ and $t_0/w_0$ in isosymmetric QCD, making use of the gauge ensembles produced by the Extended Twisted Mass Collaboration (ETMC) with $N_f=2+1+1$ flavours of Wilson-clover twisted-mass quarks including configurations close to the physical point for all dynamical flavours. The simulations are carried out at three values of the lattice spacing and the scale is set through the PDG value of the pion decay constant, yielding $w_0=0.17383(63)$ fm, $\sqrt{t_0}=0.14436(61)$ fm and $t_0/w_0=0.11969(62)$ fm. Finally, fixing the ka…
We report on a two-flavour lattice QCD determination of the $B_s\to D_s$ and $B_s\to D_s^*$ transitions, which in the heavy quark limit can be parameterised by the form factors $\mathcal{G}$, and $h_{\text A_1}$, $h_{\text A_2}$ and $h_{\text A_3}$. In the search of New Physics through tests of lepton-flavour universality, $B_s$ decay channels are complementary to $B$ decays and widely studied at $B$ factories and LHCb. The purpose of our study is to explore a suitable method to extract form factors associated with $b\to c$ currents from lattice QCD. In particular, we present numerical results…
With the ever-growing number of computing architectures, performance portability is an important aspect of (Lattice QCD) software. The Grid library provides a good framework for writing such code, as it thoroughly separates hardware-specific code from algorithmic functionality and already supports many modern architectures. We describe the implementation of a multigrid solver for Wilson clover fermions in Grid by the RQCD group. We present the features included in our implementation, discuss initial optimization efforts, and compare the performance with another multigrid implementation.
We describe our implementation of a multigrid solver for Wilson-clover fermions, which increases parallelism by solving for multiple right-hand sides (MRHS) simultaneously. The solver is based on Grid and thus runs on all computing architectures supported by the Grid framework. We present detailed benchmarks of the relevant kernels, such as hopping and clover term on the various multigrid levels, intergrid operators, and reductions. The benchmarks were performed on the JUWELS Booster system at Jülich Supercomputing Centre, which is based on Nvidia A100 GPUs. For example, solving a $24^3\times1…
Stabilized Wilson fermions are a reformulation of Wilson clover fermions that incorporates several numerical stabilizing techniques, but also a local change of the fermion action - the original clover term being replaced with an exponentiated version of it. We intend to apply the stabilized Wilson fermions toolbox to the thermodynamics of QCD, starting on the $N_f=3$ symmetric line on the Columbia plot, and to compare the results with those obtained with other fermion discretizations.
We explore and compare three mixed action setups with Wilson twisted mass sea quarks and different valence quark actions: (1) Wilson twisted mass, (2) Wilson twisted mass + clover and (3) Wilson + clover. Our main goal is to reduce lattice discretization errors in mesonic spectral quantities, in particular to reduce twisted mass parity and isospin breaking.
We present the masses of singly ($B$, $B_s$, $Λ_b$, $Σ_b$, etc.), doubly ($B_c$, $η_b$, $Υ$, $Ξ_{bc}$, $Ξ_{bb}$, etc.), and triply ($Ω_{bcc}$, $Ω_{bbc}$, $Ω_{bbb}$, etc.) heavy hadrons arising from (QCDSF-UKQCD) lattices with improved clover-Wilson light quarks. For the bottom quark, we use an $O(a,v^4)$-improved version of lattice NRQCD. Part of the bottomonia spectrum is used to provide an alternative scale and to determine the physical quark mass and radiative corrections used in the heavy-quark action. Results for spin splittings, opposite parities, and, in some cases, excited states are p…
Clover improvement is the standard choice for lattice simulations of QCD, when the lattice artefacts coming from Wilson fermions have to be reduced. However, the clover improvement is not limited to QCD, but can be applied to a wider range of theories with fermions in higher representations of the gauge group SU(N), like the adjoint fermions required by supersymmetry or by technicolor theories. We present the calculation of the clover coefficient up to one loop order with standard perturbation theory for these models. Applications of clover fermions to supersymmetric Yang-Mills theory are also…
We present high statistics ($\mathcal{O}(2\times 10^5)$ measurements) preliminary results on (i) the isovector charges, $g^{u-d}_{A,S,T}$, and form factors, $G^{u-d}_E(Q^2)$, $G^{u-d}_M(Q^2)$, $G^{u-d}_A(Q^2)$, $\widetilde G^{u-d}_P(Q^2)$, $G^{u-d}_P(Q^2)$, on six 2+1-flavor Wilson-clover ensembles generated by the JLab/W&M/LANL/MIT collaboration with lattice parameters given in Table 1. Examples of the impact of using different estimates of the excited state spectra are given for the clover-on-clover data, and as discussed in [1], the biggest difference on including the lower energy (close to…
We present an adaptive multigrid Dirac solver developed for Wilson clover fermions which offers order-of-magnitude reductions in solution time compared to conventional Krylov solvers. The solver incorporates even-odd preconditioning and mixed precision to solve the Dirac equation to double precision accuracy and shows only a mild increase in time to solution for decreasing quark mass. We show actual time to solution on production lattices in comparison to conventional Krylov solvers and will also discuss the setup process and its relative cost to the total solution time.
We present a perturbative calculation of the improvement coefficients of SU(2) gauge theory with adjoint representation Wilson-clover fermions and using Schrodinger functional boundary conditions. The computation of the boundary improvement terms is necessary for the full O(a) improvement. With two flavours of adjoint representation fermions this theory is called Minimal Walking Technicolor model.
