Disconnected contributions to the spin of the nucleon

Chambers, A. J.; Horsley, R.; Schiller, A.; Stüben, H.; Pleiter, D.; Zanotti, J. M.; Perlt, H.; Nakamura, Y.; Rakow, P. E. L.; Schierholz, G.; Young, R.

doi:10.1103/physrevd.92.114517

Cited by 58 publications

(61 citation statements)

References 33 publications

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“…We compare this with lattice QCD results from other OðaÞ-improved actions from Ref. [41] (the filled magenta triangle) by the QCDSF Collaboration [42] (the light blue cross), and by the CSSM/ QCDSF Collaboration [43] (the yellow filled right triangle). We also show results using a hybrid action from the PNDME Collaboration [44] (the open blue triangles).…”

Section: -Ptmentioning

confidence: 92%

Nucleon Spin and Momentum Decomposition Using Lattice QCD Simulations

et al. 2017

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We determine within lattice QCD the nucleon spin carried by valence and sea quarks and gluons. The calculation is performed using an ensemble of gauge configurations with two degenerate light quarks with mass fixed to approximately reproduce the physical pion mass. We find that the total angular momentum carried by the quarks in the nucleon is J uþdþs ¼ 0.408ð61Þ stat ð48Þ syst and the gluon contribution is J g ¼ 0.133ð11Þ stat ð14Þ syst , giving a total of J N ¼ 0.54ð6Þ stat ð5Þ syst that is consistent with the spin sum. For the quark intrinsic spin contribution, we obtain 1 2 ΔΣ uþdþs ¼ 0.201ð17Þ stat ð5Þ syst . All quantities are given in the modified minimal subtraction scheme at 2 GeV. The quark and gluon momentum fractions are also computed and add up to hxi uþdþs þ hxi g ¼ 0.804ð121Þ stat ð95Þ syst þ 0.267ð12Þ stat ð10Þ syst ¼ 1.07ð12Þ stat ð10Þ syst , thus satisfying the momentum sum. DOI: 10.1103/PhysRevLett.119.142002 Introduction.-The distribution of the proton spin among its constituent quarks and gluons has been a long-standing puzzle ever since the European Muon Collaboration showed in 1987 that only a fraction of the proton spin is carried by the quarks [1,2]. This was in sharp contrast to what one expected based on the quark model. This socalled proton spin crisis triggered rich experimental and theoretical activity. Recent experiments show that only 30% of the proton spin is carried by the quarks [3], while experiments at RHIC [4,5] on the determination of the gluon polarization in the proton point to a nonzero contribution [6]. A global fit to the most recent experimental data that includes the combined set of inclusive deep-inelastic scattering data from HERA and Drell-Yan data from Tevatron and LHC led to an improved determination of the valence quark distributions and the flavor separation of the up and down quarks [7]. The combined HERA data also provide improved constraints on the gluon distributions, but large uncertainties remain [7]. Obtaining the quark and gluon contributions to the nucleon spin and momentum fraction within lattice quantum chromodynamics (QCD) provides an independent input that is extremely crucial, but the computation is very challenging. This is because a complete determination must include, besides the valence, sea quark and gluon contributions that exhibit a large noise-to-signal ratio and are computationally very demanding. A first computation of the gluon spin was performed recently via the evaluation of the gluon helicity in a mixed action approach of overlap valence quarks on N f ¼ 2 þ 1 domain wall fermions that included an ensemble with pion mass 139 MeV [8]. In this Letter, we evaluate

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Section: -Ptmentioning

confidence: 92%

Nucleon Spin and Momentum Decomposition Using Lattice QCD Simulations

et al. 2017

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“…It is worth mentioning that the phenomenological value extracted from different analyses (see Refs. [56][57][58][59][60][61] of Ref. [24]) shows a spread, which, however, is significantly smaller than the discrepancy shown by the lattice data.…”

Section: Quark Momentum Fractionmentioning

confidence: 99%

“…Non-perturbatively these are unknown (for a recent study using the Feynman-Hellmann approach, see Ref. [56]), but are expected to be small since in perturbation theory they first appear to two loops. Recent results by the Cyprus group [57] show that only the scalar and axial contributions survive to two loops.…”

Section: Nucleon Spinmentioning

confidence: 99%

Hadron Structure

Constantinou¹

2015

Proceedings of the 32nd International Symposium on Lattice Field Theory — PoS(LATTICE2014)

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This is a review of recent developments in hadron structure within the framework of Lattice QCD. The main focus is on recent achievements in the evaluation of nucleon quantities, such as the axial charge, electromagnetic form factors, the Dirac and Pauli radii, the quark momentum fraction and the spin content of the nucleon, in view of simulations at pion masses very close to their physical value. A discussion of the systematic uncertainties and the computation of the disconnected contributions using dynamical simulations is also included. Results emerging the propetries of particles other than the nucleon are summarized, highlighting selected hyperon and meson form factors.

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“…Matrix elements of such operators are notoriously difficult to study via numerical simulations, due to the presence of (fermion line) disconnected diagrams, which in principle require evaluation of the full fermion propagator. In recent years there has been some progress in the numerical study of flavor singlet operators; furthermore, for some of them, a nonperturbative estimate of their renormalization has been obtained using the Feynman-Hellmann relation [2]. Perturbation theory can give an important cross check for these estimates, and provide a prototype for other operators which are more difficult to renormalize nonperturbatively.…”

Section: Introductionmentioning

confidence: 99%

Singlet versus nonsinglet perturbative renormalization of fermion bilinears

et al. 2016

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address : Department of P hysics, T emple U niversity, P hiladelphia, P A 19122 − 1801, U SA c P resent address : Department of P hysics, U niversity of M ichigan, Ann Arbor, M I 48109, U SA In this paper we present the perturbative evaluation of the difference between the renormalization functions of flavor singlet and nonsinglet bilinear quark operators on the lattice. The computation is performed to two loops and to lowest order in the lattice spacing, for a class of improved lattice actions, including Wilson, tree-level (TL) Symanzik and Iwasaki gluons, twisted mass and SLiNC Wilson fermions, as well as staggered fermions with twice stout-smeared links. In the staggered formalism, the stout smearing procedure is also applied to the definition of bilinear operators.

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Disconnected contributions to the spin of the nucleon

Cited by 58 publications

References 33 publications

Nucleon Spin and Momentum Decomposition Using Lattice QCD Simulations

Nucleon Spin and Momentum Decomposition Using Lattice QCD Simulations

Hadron Structure

Singlet versus nonsinglet perturbative renormalization of fermion bilinears

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