Abstract
We present the scale setting for a new set of gauge configurations generated with N_mathrm{f}=3+1 Wilson quarks with a non-perturbatively determined clover coefficient in a massive O(a) improvement scheme. The three light quarks are degenerate, with the sum of their masses being equal to its value in nature and the charm quark has its physical mass. We use open boundary conditions in time direction to avoid the problem of topological freezing at small lattice spacings and twisted-mass reweighting for improved stability of the simulations. The decoupling of charm at low energy allows us to set the scale by measuring the value of the low-energy quantity t_0^star /a^2, which is the flow scale t_0 at our mass point, and comparing it to an N_mathrm{f}=2+1 result in physical units. We present the details of the algorithmic setup and tuning procedure and give the bare parameters of ensembles with two lattice spacings a=0.054fm and a=0.043fm. We discuss finite volume effects and lattice artifacts and present physical results for the charmonium spectrum. In particular the hyperfine splitting between the eta _c and J/psi mesons agrees very well with its physical value.
Highlights
We present the scale setting for a new set of gauge configurations generated with Nf = 3+1 Wilson quarks with a non-perturbatively determined clover coefficient in a massive O(a) improvement scheme
As a first physics result, we measure the masses of the charmonium states ηc, J/ψ, χc0, χc1 and hc, which agree with their PDG values
The steps are to double the statistics of ensemble B and produce a third ensemble C on a 192 × 643 lattice at an even finer lattice spacing a = 0.032fm, in order to make more reliable continuum limit extrapolations
Summary
The ensembles were generated using the open-source (GPL v2) package openQCD version 1.6 [15] in plain C with MPI parallelization. This software has been successfully used in various large-scale projects. The simulations are performed on lattices of size Nt × Ns3. Gauge fields are periodic in spatial directions and absent on temporal links sticking out of the lattice, i.e. we have open boundaries in temporal direction imposed on time slice 0 and Nt − 1, the physical time extent is T = (Nt − 1)a with the lattice spacing a. For a general introduction to lattice QCD simulations with open boundary conditions and twisted-mass reweighting we refer to [17,18]
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