Yong-Chull Jang

BK using HYP-smeared staggered fermions in Nf = 2 + 1 unquenched QCD

We present results for kaon mixing parameter BK calculated using HYP-smeared improved staggered fermions on the MILC asqtad lattices. We use three lattice spacings (a ≈ 0.12, 0.09 and 0.06 fm), ten different valence quark masses (m ≈ ms/10 − ms), and several light sea-quark masses in order to control the continuum and chiral extrapolations. We derive the next-to-leading order staggered chiral perturbation theory (SChPT) results necessary to fit our data, and use these results to do extrapolations based both on SU(2) and SU(3) SChPT. The SU(2) fitting is particularly straightforward because parameters related to taste-breaking and matching errors appear only at next-to-next-to-leading order. We match to the continuum renormalization scheme (NDR) using one-loop perturbation theory. Our final result is from the SU(2) analysis, with the SU(3) result providing a (less accurate) cross check. We find BK(NDR,µ = 2 GeV) = 0.529 ± 0.009 ± 0.032 and b BK = BK(RGI) = 0.724 ± 0.012 ± 0.043, where the first error is statistical and the second systematic. The error is dominated by the truncation error in the matching factor. Our results are consistent with those obtained using valence domain-wall fermions on lattices generated with asqtad or domain-wall sea quarks.

Kaon B parameter from improved staggered fermions in N(f)=2+1 QCD.

We present a calculation of the kaon B parameter B(K) using lattice QCD. We use improved staggered valence and sea fermions, the latter generated by the MILC Collaboration with N(f)=2+1 light flavors. To control discretization errors, we use four different lattice spacings ranging down to a≈0.045 fm. The chiral and continuum extrapolations are done using SU(2) staggered chiral perturbation theory. Our final result is B(K)=0.727±0.004(stat)±0.038(syst), where the dominant systematic error is from our use of truncated (one-loop) matching factors.

Neutral kaon mixing from new physics: matrix elements in

We present results for matrix elements of

N_f=2+1

\Delta S=2

lattice QCD

four-fermion operators arising generically in models of new physics. These are needed to constrain such models using the measured values of

Axial-vector form factors of the nucleon from lattice QCD

\varepsilon_K

Isovector charges of the nucleon from 2 + 1 -flavor QCD with clover fermions

and

Standard Model evaluation of

\Delta M_K

\varepsilon_K

. We use lattice QCD with 2+1 flavors of improved staggered fermions on lattices generated by the MILC collaboration. We extrapolate to the continuum from three lattice spacings ranging down to

using lattice QCD inputs for

a\approx 0.045\;