A
bstract
By matching Wilson twisted mass lattice QCD determinations of pseudoscalar meson masses to Wilson Chiral Perturbation Theory we determine the low-energy constants
,
and their linear ...combination
c
2
. We explore the dependence of these low-energy constants on the choice of the lattice action and on the number of dynamical flavours.
We present a lattice calculation of the leading-order electromagnetic and strong isospin-breaking corrections to the hadronic vacuum polarization (HVP) contribution to the anomalous magnetic moment ...of the muon. We employ the gauge configurations generated by the European Twisted Mass Collaboration with Nf = 2 + 1 + 1 dynamical quarks at three values of the lattice spacing (a≃0.062,0.082,0.089 fm) with pion masses between ≃210 and ≃450 MeV. The results are obtained by adopting the RM123 approach in the quenched-QED approximation, which neglects the charges of the sea quarks. Quark disconnected diagrams are not included. After the extrapolations to the physical pion mass and to the continuum and infinite-volume limits the contributions of the light, strange, and charm quarks are, respectively, equal to δaμHVP(ud)=7.1(2.5)×10−10, δaμHVP(s)=−0.0053(33)×10−10, and δaμHVP(c)=0.0182(36)×10−10. At leading order in αem and (md−mu)/ΛQCD we obtain δaμHVP(udsc)=7.1(2.9)×10−10, which is currently the most accurate determination of the isospin-breaking corrections to aμHVP.
We present results of lattice QCD simulations with mass-degenerate up and down and mass-split strange and charm (
N
f
= 2 + 1 + 1) dynamical quarks using Wilson twisted mass fermions at maximal ...twist. The tuning of the strange and charm quark masses is performed at two values of the lattice spacing
a
≈ 0:078 fm and
a
≈ 0:086 fm with lattice sizes ranging from
L
≈ 1:9 fm to
L
≈ 2:8 fm. We measure with high statistical precision the light pseudoscalar mass
m
PS
and decay constant
f
PS
in a range 270 ≲
m
PS
≲ 510 MeV and determine the low energy parameters
f
0
and
of SU(2) chiral perturbation theory. We use the two values of the lattice spacing, several lattice sizes as well as different values of the light, strange and charm quark masses to explore the systematic effects. A first study of discretisation effects in light-quark observables and a comparison to
N
f
= 2 results are performed.
We present an investigation of the electromagnetic pion form factor, Fπ(Q2), at small values of the four-momentum transfer Q2 (≲0.25 GeV2), based on the gauge configurations generated by the ...European Twisted Mass Collaboration with Nf=2 twisted-mass quarks at maximal twist including a clover term. Momentum is injected using nonperiodic boundary conditions and the calculations are carried out at a fixed lattice spacing (a≃0.09 fm) and with pion masses equal to its physical value, 240 MeV and 340 MeV. Our data are successfully analyzed using chiral perturbation theory at next-to-leading order in the light-quark mass. For each pion mass two different lattice volumes are used to take care of finite size effects. Our final result for the squared charge radius is ⟨r2⟩π=0.443(29) fm2, where the error includes several sources of systematic errors except the uncertainty related to discretization effects. The corresponding value of the SU(2) chiral low-energy constant ℓ¯6 is equal to ℓ¯6=16.2(1.0).
η and η' mixing from lattice QCD Michael, C; Ottnad, K; Urbach, C
Physical review letters,
2013-Nov-01, Letnik:
111, Številka:
18
Journal Article
Recenzirano
We present a lattice QCD computation of η and η' masses and mixing angles, for the first time controlling continuum and quark mass extrapolations. The results for M(η) = 551(8)(stat) (6)(yst) MeV and ...M(η') = 1006(54)(stat)(38)(syst)(+61)(ex) MeV are in excellent agreement with experiment. Our data show that the mixing in the quark flavor basis can be described by a single mixing angle of Ø = 46(1)(stat)(3)(syst)° indicating that the η' is mainly a flavor singlet state.
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