1,721,008 research outputs found
The axial charge of the nucleon on the lattice and in chiral perturbation theory
No full textWe present recent Monte Carlo data for the axial charge of the nucleon obtained by the QCDSF-UKQCD collaboration for Nf=2 dynamical quarks. We compare them with formulae from chiral perturbation theory in finite and infinite volume and find a remarkably consistent picture
Baryon axial charges and momentum fractions with Nf=2+1 dynamical fermions
Full text linkWe report on recent results of the QCDSF/UKQCD Collaboration on investigations of baryon structure using configurations generated with Nf=2+1 dynamical flavours of O(a) improved Wilson fermions. With the strange quark mass as an additional dynamical degree of freedom in our simulations we avoid the need for a partially quenched approximation when investigating the properties of particles containing a strange quark, e.g. the hyperons. In particular, we will focus on the nucleon and hyperon axial coupling constants and quark momentum fractions.M. Göckeler, Ph. Hägler, R. Horsley, Y. Nakamura, D. Pleiter, P.E.L. Rakow, A. Schäfer, G. Schierholz, H. Stüben, F. Winter and J.M. Zanotti (QCDSF/UKQCD Collaboration
Hyperon form factors from Nf=2+1 QCD
Full text linkWe present results from the QCDSF/UKQCD collaboration for the electromagnetic and semi-leptonic form factors for the hyperons. The simulations are performed on our new ensembles generated with 2+1 flavours of dynamical (a)-improved Wilson fermions. A unique feature of these configurations is the quark masses are tuned so that the singlet quark mass is held fixed as its physical value. We use 5 such choices of the individual quark masses on 24 3 x 48 lattices with a lattice spacing of about 0.078 fm.M. Göckeler, Ph. Hägler, R. Horsley, Y. Nakamura, D. Pleiter, P.E.L. Rakow, A. Schäfer, G. Schierholz, H. Stüben, F. Winter and J.M. Zanotti (QCDSF/UKQCD Collaboration)http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=10
Nucleon structure from lattice QCD
No full textAlso published as a book chapter: The IX International Conference on Quark Confinement and the Hadron Spectrum – QCHS IX: Madrid, Spain 30 August - 3 September 2010 / F.J. Llanes-Estrada, J.R. Peláez (eds.): pp.281-283Lattice simulations of hadronic structure are now reaching a level where they are able to not only complement, but also provide guidance to current and forthcoming experimental programmes.By considering new simulations at low quark masses and on large volumes, we review the recent progress that has been made in this area by the QCDSF/UKQCD collaboration. In particular, results obtained close to the physical point for several quantities, including electromagnetic form factors and moments of parton distribution functions, show some indication of approaching their phenomenological values. © 2011 American Institute of Physics.J.M. Zanotti [QCDSF/UKQCD Collaboration
Probing Nucleon Structure on the Lattice.
No full textThe QCDSF/UKQCD Collaboration has an ongoing program to calculate nucleon matrix elements with two flavours of dynamical O (a) improved Wilson fermions. Here we present recent results on the electromagnetic form factors, the quark momentum fraction and the first three moments of the nucleon’s spin-averaged and spin-dependent generalised parton distributions, including preliminary results with pion masses as low as 320MeV
Transverse spin densities of octet baryons using Lattice QCD
No full text© Copyright owned by the author(s). We present results from the QCDSF/UKQCD collaboration for the transverse spin densities of octet baryons obtained from simulations using Nf = 2+1 flavours of O(a)-improved Wilson fermions. These densities are revealed through an analysis of the electromagnetic and tensor form factors of the octet baryons at two different lattice spacings with pion masses as low as 220 MeV. We find SU(3) flavour-breaking effects of the form factors and use these to extrapolate to the physical mass. Constructing combinations of Fourier transformed form factors reveal non-trivial spin densities in the transverse plane, with similar deformations across the baryon octet
Nonperturbative improvement of stout-smeared three-flavor clover fermions
Full text linkWe discuss a three-flavor lattice QCD action with clover improvement in which the fermion matrix has single level stout smearing for the hopping terms together with unsmeared links for the clover term. With the (tree-level) Symanzik improved gluon action this constitutes the stout link nonperturbative clover or SLiNC action. To cancel O(a) terms the clover term coefficient has to be tuned. We present here results of a nonperturbative determination of this coefficient using the Schrödinger functional and as a by-product a determination of the critical hopping parameter. Comparisons of the results are made with lowest order perturbation theory.N. Cundy, M. Göckeler, R. Horsley, T. Kaltenbrunner, A. D. Kennedy, Y. Nakamura, H. Perlt, D. Pleiter, P. E. L. Rakow, A. Schäfer, G. Schierholz, A. Schiller, H. Stüben, and J. M. Zanotti (QCDSF-UKQCD Collaboration
SU(3) flavour breaking and baryon structure
No full textWe present results from the QCDSF/UKQCD collaboration for hyperon electromagnetic form factors and axial charges obtained from simulations using Nf=2+1 flavours of O(a)-improved Wilson fermions. We also consider matrix elements relevant for hyperon semileptonic decays. We find flavour-breaking effects in hyperon magnetic moments which are consistent with experiment, while our results for the connected quark spin content indicates that quarks contribute more to the spin of the Xi baryon than they do to the proton
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