Strangeness Contribution to the Proton Spin from Lattice QCD

Bali, Gunnar S.; Collins, Sara; Göckeler, M.; Horsley, R.; Nakamura, Y.; Nobile, Andrea; Pleiter, D.; Rakow, P. E. L.; Schäfer, Andreas; Schierholz, G.; Zanotti, J. M.

doi:10.1103/physrevlett.108.222001

Cited by 91 publications

(72 citation statements)

References 48 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: 90%

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: 90%

Nucleon Spin and Momentum Decomposition Using Lattice QCD Simulations

et al. 2017

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“…Because of the indirect nature of this estimate, the shift (25) will not be applied to the (chirally extrapolated) central value for Ás obtained in this work, but will be treated as a systematic uncertainty. It should be remarked that the considerations for the clover case [11] referred to above pertain to lattices with a substantially finer spacing than used here (0.073 vs 0.124 fm). However, adjusting for this is expected to modify (25) merely by a few percent and thus is negligible in the present context.…”

Section: B Axial Vector Matrix Elementmentioning

confidence: 97%

Strange quark contributions to nucleon mass and spin from lattice QCD

Engelhardt

2012

Phys. Rev. D

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Contributions of strange quarks to the mass and spin of the nucleon, characterized by the observables f_Ts and Delta s, respectively, are investigated within lattice QCD. The calculation employs a 2+1-flavor mixed-action lattice scheme, thus treating the strange quark degrees of freedom in dynamical fashion. Numerical results are obtained at three pion masses, m_pi = 495 MeV, 356 MeV, and 293 MeV, renormalized, and chirally extrapolated to the physical pion mass. The value extracted for Delta s at the physical pion mass in the MSbar scheme at a scale of 2 GeV is Delta s = -0.031(17), whereas the strange quark contribution to the nucleon mass amounts to f_Ts =0.046(11). In the employed mixed-action scheme, the nucleon valence quarks as well as the strange quarks entering the nucleon matrix elements which determine f_Ts and Delta s are realized as domain wall fermions, propagators of which are evaluated in MILC 2+1-flavor dynamical asqtad quark ensembles. The use of domain wall fermions leads to mild renormalization behavior which proves especially advantageous in the extraction of f_Ts.Comment: 29 pages, 5 figures; version accepted by journal. Minute reformulations, typos fixe

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“…For these quantities, we use results from a lattice QCD computation presented in [47], namely ∆ u = 0.787 ± 0.158, ∆ d = −0.319 ± 0.066, ∆ s = −0.02 ± 0.011 [47]. As above, we fix all quantities to their central values.…”

Section: Jhep09(2014)081mentioning

confidence: 99%

Profile likelihood maps of a 15-dimensional MSSM

Strege

Bertone

Besjes

et al. 2014

J. High Energ. Phys.

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We present statistically convergent profile likelihood maps obtained via global fits of a phenomenological Minimal Supersymmetric Standard Model with 15 free parameters (the MSSM-15), based on over 250M points. We derive constraints on the model parameters from direct detection limits on dark matter, the Planck relic density measurement and data from accelerator searches. We provide a detailed analysis of the rich phenomenology of this model, and determine the SUSY mass spectrum and dark matter properties that are preferred by current experimental constraints. We evaluate the impact of the measurement of the anomalous magnetic moment of the muon (g − 2) on our results, and provide an analysis of scenarios in which the lightest neutralino is a subdominant component of the dark matter. The MSSM-15 parameters are relatively weakly constrained by current data sets, with the exception of the parameters related to dark matter phenomenology (M 1 , M 2 , µ), which are restricted to the sub-TeV regime, mainly due to the relic density constraint. The mass of the lightest neutralino is found to be < 1.5 TeV at 99% C.L., but can extend up to 3 TeV when excluding the g − 2 constraint from the analysis. Low-mass bino-like neutralinos are strongly favoured, with spin-independent scattering cross-sections extending to very small values, ∼ 10 −20 pb. ATLAS SUSY null searches strongly impact on this mass range, and thus rule out a region of parameter space that is outside the reach of any current or future direct detection experiment. The best-fit point obtained after inclusion of all data corresponds to a squark mass of 2.3 TeV, a gluino mass of 2.1 TeV and a 130 GeV neutralino with a spin-independent cross-section of 2.4×10 −10 pb, which is within the reach of future multi-ton scale direct detection experiments and of the upcoming LHC run at increased centre-of-mass energy.

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Strangeness Contribution to the Proton Spin from Lattice QCD

Cited by 91 publications

References 48 publications

Nucleon Spin and Momentum Decomposition Using Lattice QCD Simulations

Nucleon Spin and Momentum Decomposition Using Lattice QCD Simulations

Strange quark contributions to nucleon mass and spin from lattice QCD

Profile likelihood maps of a 15-dimensional MSSM

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