Highly improved staggered quarks on the lattice with applications to charm physics

Abstract

We use perturbative Symanzik improvement to create a new staggered-quark action (HISQ) that has greatly reduced one-loop taste-exchange errors, no tree-level order a 2 errors, and no tree-level order (am) 4 errors to leading order in the quark's velocity v/c. We demonstrate with simulations that the resulting action has taste-exchange interactions that are at least 3-4 times smaller than the widely used ASQTAD action. We show how to estimate errors due to taste exchange by comparing ASQTAD and HISQ simulations, and demonstrate with simulations that such errors are no more than 1% when HISQ is used for light quarks at lattice spacings of 1/10 fm or less. The suppression of (am) 4 errors also makes HISQ the most accurate discretization currently available for simulating c quarks. We demonstrate this in a new analysis of the ψ − ηc mass splitting using the HISQ action on lattices where amc = 0.43 and 0.66, with full-QCD gluon configurations (from MILC). We obtain a result of 111(5) MeV which compares well with experiment. We discuss applications of this formalism to D physics and present our first high-precision results for Ds mesons.

Lattice QCD study of the radiative decays J/ψ → η c γ and h c → η c γ

“…[40], ∆ = (111 ± 5) MeV. Once more, this implicitly suggests that the contribution of the OZI breaking JHEP01(2013)028 diagrams in the charmonia, neglected in our computations, are very small (c.f.…”

Fluctuations of conserved charges at finite temperature from lattice QCD

“…[17] for details). The stout-smearing [18] yields an improved discretization of the fermion-gauge vertex and reduces a staggered artefact, the so-called taste violation (analogously to ours, an alternative link-smearing scheme, the HISQ action [19] suppresses the taste breaking in a similar way. The latter is used by the hotQCD collaboration in their latest studies [2]).…”

Pseudoscalar meson electromagnetic form factor at high Q2 from full lattice QCD

“…These are implemented by using the 'twisted boundary condition' method [41] and are chosen to be in the (1,1,1) direction to minimise discretisation effects. We use η s mesons made with the local γ 5 (Goldstone) operator; in staggered quark parlance this corresponds to spin-taste γ 5 ⊗ γ 5 [34]. For our 3-point correlation functions we use a 1-link temporal vector current with spin-taste γ 0 ⊗ 1.…”

“…D i accounts for the heavier-than-physical quark masses in the sea, using δm = u,d,s (m q − m tuned q )/m tuned s [30] and dividing by a factor of 10 to convert this to a suitable chiral perturbation theory expansion parameter. We take priors on the B i , C i and D i of 0.0(1.0) but on B 1 of 0.0(5), because leading a 2 errors are suppressed by α s in the HISQ formalism [34]. For the A i , the coefficients of the z-expansion in the continuum and chiral limits, we take priors of 0.0(2.0), twice as conservative as the Bayesian probability function would suggest.…”

“…We use the Highly Improved Staggered Quark (HISQ) formalism designed [34], and shown [31,[35][36][37], to have very small discretisation errors from the lattice spacing. We work on gluon field configurations generated by the MILC collaboration [38,39] that include HISQ u, d, s and c quarks in the sea and also have a highly-improved gluon action [40].…”