48 research outputs found
Reply to "Comment on `Lattice determination of Sigma - Lambda mixing' "
In this Reply, we respond to the above Comment. Our computation [Phys. Rev. D
91 (2015) 074512] only took into account pure QCD effects, arising from quark
mass differences, so it is not surprising that there are discrepancies in
isospin splittings and in the Sigma - Lambda mixing angle. We expect that these
discrepancies will be smaller in a full calculation incorporating QED effects.Comment: 5 page
QCD with light Wilson quarks on fine lattices (II): DD-HMC simulations and data analysis
In this second report on our recent numerical simulations of two-flavour QCD,
we provide further technical details on the simulations and describe the
methods we used to extract the meson masses and decay constants from the
generated ensembles of gauge fields. Among the topics covered are the choice of
the DD-HMC parameters, the issue of stability, autocorrelations and the
statistical error analysis. Extensive data tables are included as well as a
short discussion of the quark-mass dependence in partially quenched QCD,
supplementing the physics analysis that was presented in the first paper in
this series.Comment: TeX source, 35 pages, figures include
A lattice determination of Sigma - Lambda mixing
Isospin breaking effects in baryon octet (and decuplet) masses are due to a
combination of up and down quark mass differences and electromagnetic effects
and lead to small mass splittings. Between the Sigma and Lambda this mass
splitting is much larger, this being mostly due to their different
wavefunctions. However when isospin is broken, there is a mixing between
between these states. We describe the formalism necessary to determine the QCD
mixing matrix and hence find the mixing angle and mass splitting between the
Sigma and Lambda particles due to QCD effects.Comment: 40 pages, 5 figures, published versio
A Feynman-Hellmann approach to the spin structure of hadrons
We perform a Nf = 2 + 1 lattice QCD simulation to determine the quark spin
fractions of hadrons using the Feynman-Hellmann theorem. By introducing an
external spin operator to the fermion action, the matrix elements relevant for
quark spin fractions are extracted from the linear response of the hadron
energies. Simulations indicate that the Feynman-Hellmann method offers
statistical precision that is comparable to the standard three-point function
approach, with the added benefit that it is less susceptible to excited state
contamination. This suggests that the Feynman-Hellmann technique offers a
promising alternative for calculations of quark line disconnected contributions
to hadronic matrix elements. At the SU(3)-flavour symmetry point, we find that
the connected quark spin fractions are universally in the range 55-70% for
vector mesons and octet and decuplet baryons. There is an indication that the
amount of spin suppression is quite sensitive to the strength of SU(3)
breaking.Comment: 13 pages, 7 figure
Axial and tensor charge of the nucleon with dynamical fermions
We present preliminary results for the axial and tensor charge of the nucleon
obtained from simulations with N_f=2 clover fermions. A comparison with chiral
perturbation theory is attempted.Comment: Talk presented at Lattice2004(weak), Fermilab, June 21-26, 2004, 3
pages, 3 figures, v2: one reference added, v3: acknowledgement extende
QED effects in the pseudoscalar meson sector
In this paper we present results on the pseudoscalar meson masses from a fully dynamical simulation of QCD+QED, concentrating particularly on violations of isospin symmetry. We calculate the π +-π 0 splitting and also look at other isospin violating mass differences. We have presented results for these isospin splittings in [1]. In this paper we give more details of the techniques employed, discussing in particular the question of how much of the symmetry violation is due to QCD, arising from the different masses of the u and d quarks, and how much is due to QED, arising from the different charges of the quarks. This decomposition is not unique, it depends on the renormalisation scheme and scale. We suggest a renormalisation scheme in which Dashen’s theorem for neutral mesons holds, so that the electromagnetic self-energies of the neutral mesons are zero, and discuss how the self-energies change when we transform to a scheme such as M S, in which Dashen’s theorem for neutral mesons is violated
Moments of generalized parton distributions and quark angular momentum of the nucleon
The internal structure of hadrons is important for a variety of topics,
including the hadron form factors, proton spin and spin asymmetry in polarized
proton scattering.
For a systematic study generalized parton distributions (GPDs) encode
important information on hadron structure in the entire impact parameter space.
We report on a computation of nucleon GPDs based on simulations with two
dynamical non-perturbatively improved Wilson quarks with pion masses down to
350MeV. We present results for the total angular momentum of quarks with chiral
extrapolation based on covariant baryon chiral perturbation theory.Comment: Presented at 25th International Symposium on Lattice Field Theory,
Regensburg, Germany, 30 Jul - 4 Aug 200