We present results for several light hadronic quantities (f sub(pi), f sub(K), B sub(K), m sub(ud), m sub(s), t super(1/2) sub(0), w sub(0)) obtained from simulations of 2+1 flavor domain wall ...lattice QCD with large physical volumes and nearly physical pion masses at two lattice spacings. We perform a short, O(3)%, extrapolation in pion mass to the physical values by combining our new data in a simultaneous chiral/continuum "global fit" with a number of other ensembles with heavier pion masses. We use the physical values of m sub(pi), m sub(K) and m sub(Omega) to determine the two quark masses and the scale-all other quantities are outputs from our simulations. We obtain results with subpercent statistical errors and negligible chiral and finite-volume systematics for these light hadronic quantities, including f sub(pi)=130.2(9)MeV; f sub(K)=155.5(8)MeV; the average up/down quark mass and strange quark mass in the MS scheme at 3 GeV, 2.997(49) and 81.64(1.17) MeV respectively; and the neutral kaon mixing parameter, BK, in the renormalization group invariant scheme, 0.750(15) and the MS scheme at 3 GeV, 0.530(11).
We present a lattice QCD calculation of the ΔI = 1/2, K → π π decay amplitude A 0 and ϵ ′, the measure of direct C P violation in K → π π decay, improving our 2015 calculation 1 of these quantities. ...Both calculations were performed with physical kinematics on a 323 × 64 lattice with an inverse lattice spacing of a−1 = 1.3784(68) GeV . However, the current calculation includes nearly 4 times the statistics and numerous technical improvements allowing us to more reliably isolate the π π ground state and more accurately relate the lattice operators to those defined in the standard model. We find Re(A0) = 2.99(0.32)(0.59) × 10−7 GeV and Im(A0) = − 6.98(0.62)(1.44) × 10−11 GeV, where the errors are statistical and systematic, respectively. The former agrees well with the experimental result Re(A0) = 3.3201(18) × 10−7 GeV . These results for A0 can be combined with our earlier lattice calculation of A2 2 to obtain Re(ϵ′/ϵ) = 21.7(2.6)(6.2)(5.0) × 10−4, where the third error represents omitted isospin breaking effects, and Re(A0) / Re(A2) = 19.9(2.3)(4.4). The first agrees well with the experimental result of Re(ϵ′/ϵ) = 16.6(2.3) × 10−4. A comparison of the second with the observed ratio Re(A0) / Re(A2) = 22.45(6), demonstrates the standard model origin of this " ΔI = 1/2 rule" enhancement.
We report the first lattice QCD calculation of the complex kaon decay amplitude A_{0} with physical kinematics, using a 32³×64 lattice volume and a single lattice spacing a, with 1/a=1.3784(68) GeV. ...We find Re(A_{0})=4.66(1.00)(1.26)×10(-7) GeV and Im(A_{0})=-1.90(1.23)(1.08)×10(-11) GeV, where the first error is statistical and the second systematic. The first value is in approximate agreement with the experimental result: Re(A_{0})=3.3201(18)×10(-7) GeV, while the second can be used to compute the direct CP-violating ratio Re(ϵ^{'}/ϵ)=1.38(5.15)(4.59)×10^{-4}, which is 2.1σ below the experimental value 16.6(2.3)×10(-4). The real part of A_{0} is CP conserving and serves as a test of our method while the result for Re(ϵ^{'}/ϵ) provides a new test of the standard model theory of CP violation, one which can be made more accurate with increasing computer capability.
An overview of the kaon physics program of the RBC and UKQCD collaborations will be presented with a focus on the lattice calculation of K → ππ decay and the direct CP violation parameter ε′. We will ...describe substantial improvements to our earlier 2015 K → ππ calculation, including the use of three independent ππ interpolating operators and the results we obtain for I = 0 ππ scattering for energies at and below the kaon mass. While the new result for ϵ′ is not yet complete, the enhanced statistics and improved analysis that underlies our expanded calculation will be presented.
We report on the first complete calculation of the KL-KS mass difference, AMK, using lattice QCD. The calculation is performed on a 2+1 flavor, domain wall fermion ensemble with a 330 MeV pion mass ...and a 575 MeV kaon mass. We use a quenched charm quark with a 949 MeV mass to implement Glashow-Iliopoulos-Maiani cancellation. For these heavier-than-physical particle masses, we obtain Delta MK=3.19(41)(96)x10-12 MeV, quite similar to the experimental value. Here the first error is statistical, and the second is an estimate of the systematic discretization error. An interesting aspect of this calculation is the importance of the disconnected diagrams, a dramatic failure of the Okubo-Zweig-Iizuka rule.
We discuss G -parity lattice boundary conditions as a means to impose momentum on the pion ground state without breaking isospin symmetry. This technique is expected to be critical for the precision ...measurement of K → ( π π ) I = 0 matrix elements where physical kinematics demands moving pions in the final state and the statistical noise caused by disconnected contributions will make it difficult to use multiexponential fits to isolate this as an excited state. We present a formalism for computing hadronic Green's functions with G -parity boundary conditions, derive the discretized action and its symmetries, discuss how the strange quark can be introduced and detail techniques for the numerical implementation of these boundary conditions. We demonstrate and test these methods using several 1 6 3 × 32 dynamical domain wall ensembles with a 420 MeV pion mass and G -parity boundary conditions in one and two spatial directions.
There has been much speculation as to the origin of the ΔI=1/2 rule (ReA0/ReA2≃22.5). We find that the two dominant contributions to the ΔI=3/2, K→ππ correlation functions have opposite signs, ...leading to a significant cancelation. This partial cancelation occurs in our computation of ReA2 with physical quark masses and kinematics (where we reproduce the experimental value of A2) and also for heavier pions at threshold. For ReA0, although we do not have results at physical kinematics, we do have results for pions at zero momentum with mπ≃420 MeV ReA0/ReA2=9.1(2.1) and mπ≃330 MeV ReA0/ReA2=12.0(1.7). The contributions which partially cancel in ReA2 are also the largest ones in ReA0, but now they have the same sign and so enhance this amplitude. The emerging explanation of the ΔI=1/2 rule is a combination of the perturbative running to scales of O(2 GeV), a relative suppression of ReA2 through the cancelation of the two dominant contributions, and the corresponding enhancement of ReA0. QCD and electroweak penguin operators make only very small contributions at such scales.
η and η' mesons from lattice QCD Christ, N H; Dawson, C; Izubuchi, T ...
Physical review letters,
12/2010, Letnik:
105, Številka:
24
Journal Article
Recenzirano
The large mass of the ninth pseudoscalar meson, the η', is believed to arise from the combined effects of the axial anomaly and the gauge field topology present in QCD. We report a realistic, ...2+1-flavor, lattice QCD calculation of the η and η' masses and mixing which confirms this picture. The physical eigenstates show small octet-singlet mixing with a mixing angle of θ=-14.1(2.8)°. Extrapolation to the physical light quark mass gives, with statistical errors only, mη=573(6) MeV and mη'=947(142) MeV, consistent with the experimental values of 548 and 958 MeV.
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