Opposite-parity contaminations in lattice nucleon form factors

Stokes, Finn M.; Kamleh, Waseem; Leinweber, Derek B.

doi:10.1103/physrevd.99.074506

Cited by 16 publications

(32 citation statements)

References 30 publications

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“…4, for each pion mass considered, the extracted squared charge radii for this first negative-parity excitation are consistent with the radii of the ground-state proton and neutron at the same mass, as obtained in Ref. [1]. This suggests that the size of this finite-volume state is similar to that of the ground-state nucleon.…”

Section: Source Momentum Psupporting

confidence: 88%

“…These charge radii are similar to the charge radii of the individual quark sectors in the ground state examined in Ref. [1], (0.662(12) fm for the doubly represented quark flavour and 0.633(12) fm for the singly represented quark flavour). The doubly represented quark sector agrees to within one standard deviation.…”

Section: A Ge For the First Negative-parity Excitationsupporting

confidence: 82%

“…At all five masses, the electric form factor for the second negative-parity excitation of the neutron is approximately zero. At the heaviest three pion masses, the linear combinations of the quark-sector dipole fits once again provide charge radii consistent with the ground-state nucleon at the same quark mass [1]. This suggests that this finitevolume excitation is also of similar size to the groundstate nucleon, as seen in Fig.…”

Section: Ge For the Second Negative-parity Excitationsupporting

confidence: 63%

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Elastic Form Factors of Nucleon Excitations

Stokes

2019

Structure of Nucleon Excited States From Lattice QCD

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The recent development of the parity-expanded variational analysis (PEVA) technique makes lattice QCD studies of the form factors of baryon excitations possible. In this paper, we present Sachs electromagnetic form factors for excitations of the proton and neutron. We study the two lowestlying odd-parity excitations and demonstrate that at heavier pion masses, these states are dominated by behaviour consistent with constituent quark models for the N * (1535) and N * (1650), respectively. At pion masses approaching the physical point, meson-baryon contributions are observed to play an increasing role. We also study the lowest-lying localised even-parity excitation, and find that its form factors are consistent with a radial excitation of the ground state nucleon. A comparison of the results from the PEVA analysis with those from a conventional variational analysis exposes the necessity of the PEVA approach in baryon excited-state studies.

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Section: Source Momentum Psupporting

confidence: 88%

Section: A Ge For the First Negative-parity Excitationsupporting

confidence: 82%

Section: Ge For the Second Negative-parity Excitationsupporting

confidence: 63%

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Elastic Form Factors of Nucleon Excitations

Stokes

2019

Structure of Nucleon Excited States From Lattice QCD

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“…Variational approaches have been used to study nucleon structure in Refs. [5][6][7][8][9], which used bases of interpolators with different smearing widths and different site-local spin structures, and Ref. [10], which used the distillation method to enable the use of interpolators with a variety of local structures including covariant derivatives.…”

Section: Introductionmentioning

confidence: 99%

Excited-state effects in nucleon structure on the lattice using hybrid interpolators

et al. 2019

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It would be very useful to find a way of reducing excited-state effects in lattice QCD calculations of nucleon structure that has a low computational cost. We explore the use of hybrid interpolators, which contain a nontrivial gluonic excitation, in a variational basis together with the standard interpolator with tuned smearing width. Using the clover discretization of the field strength tensor, a calculation using a fixed linear combination of standard and hybrid interpolators can be done using the same number of quark propagators as a standard calculation, making this a cost-effective option. We find that such an interpolator, optimized by solving a generalized eigenvalue problem, reduces excited-state contributions in two-point correlators. However, the effect in three-point correlators, which are needed for computing nucleon matrix elements, is mixed: for some matrix elements such as the tensor charge, excited-state effects are suppressed, whereas for others such as the axial charge, they are enhanced. The results illustrate that the variational method is not guaranteed to reduce the net contribution from excited states except in its asymptotic regime, and suggest that it may be important to use a large basis of interpolators capable of isolating all of the relevant low-lying states. * jeremy.green@desy.de 1 The comparison is more difficult when using the distillation method, which uses timeslice sources rather than the point sources used in standard calculations. 2 The resulting basis of interpolators is similar to the one called B 3 in Ref. [10].

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“…The computational cost increases with each operator insertion and with each value of τ. This approach has been used recently in some variational studies by the CSSM group [21,22].…”

Section: Numerical Studiesmentioning

confidence: 99%

Systematics in nucleon matrix element calculations

Green¹

2019

Proceedings of the 36th Annual International Symposium on Lattice Field Theory — PoS(LATTICE2018)

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Opposite-parity contaminations in lattice nucleon form factors

Cited by 16 publications

References 30 publications

Elastic Form Factors of Nucleon Excitations

Elastic Form Factors of Nucleon Excitations

Excited-state effects in nucleon structure on the lattice using hybrid interpolators

Systematics in nucleon matrix element calculations

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