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doi:10.1103/physrevd.90.012007

Cited by 76 publications

(51 citation statements)

References 52 publications

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“…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].…”

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confidence: 99%

Nucleon Spin and Momentum Decomposition Using Lattice QCD Simulations

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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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Nucleon Spin and Momentum Decomposition Using Lattice QCD Simulations

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“…In an effort to search for the missing proton spin, recent analyses [4,5] of the high-statistics 2009 STAR [6] and PHENIX [7] experiments at RHIC showed evidence of non-zero glue helicity ∆G in the proton. For Q 2 = 10 GeV 2 , the glue helicity distribution ∆g(x, Q 2 ) is found to be positive and away from zero in the momentum fraction region x < 0.05.…”

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Glue Spin and Helicity in the Proton from Lattice QCD

et al. 2017

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We report the first lattice QCD calculation of the glue spin in the nucleon. The lattice calculation is carried out with valence overlap fermions on 2+1 flavor DWF gauge configurations on four lattice spacings and four volumes including an ensemble with physical values for the quark masses. The glue spin SG in the Coulomb gauge in the MS scheme is obtained with the 1-loop perturbative matching. We find the results fairly insensitive to lattice spacing and quark masses. We also find that the proton momentum dependence of SG in the range 0 ≤ | p| < 1.5 GeV is very mild, and we determine it in the large momentum limit to be SG = 0.251(47)(16) at the physical pion mass in the MS scheme at µ 2 = 10 GeV 2 . If the matching procedure in large momentum effective theory is neglected, SG is equal to the glue helicity measured in high-energy scattering experiments.Introduction: Deep-inelastic scattering experiments reveal that contrary to the naive quark model, the quark spin contribution to the proton spin is quite small, about 30% [1][2][3]. In an effort to search for the missing proton spin, recent analyses [4,5] of the high-statistics 2009 STAR [6] and PHENIX [7] experiments at RHIC showed evidence of non-zero glue helicity ∆G in the proton. For Q 2 = 10 GeV 2 , the glue helicity distribution ∆g(x, Q 2 ) is found to be positive and away from zero in the momentum fraction region x < 0.05. However, the results are limited by very large uncertainty in this region.The recent COMPASS analysis explored ∆g(x) from the scaling violation of ∆q(x), and the highly distinct solutions of ∆g(x) can be obtained with different parameterizations of ∆q(x) [8]. Therefore, it hints that if a high precision ∆g(x) can be obtained directly, it will benefit our understanding of the parameterizations of ∆q(x) and provide more information about the role of quark spin in the proton.Given the importance of ∆g(x) to explain the origin of the proton spin, and the fact that significant efforts are devoted to its precise experimental determination, a theoretical understanding and calculation of ∆G is highly desired. ∆G is defined as the first moment of the glue helicity distribution ∆g(x) [9],where the light front coordinates areThe proton plane wave state is written as |P S , with momentum P µ = (P, 0, 0, P ) and polarization S. The light-cone gauge-link L(ξ − , 0) =is defined in the adjoint representation. It connects the gauge field tensor and its dual,F αβ = 1 2 αβµν F µν , to construct a gauge invariant operator. After integrating over x, one can define the gauge-invariant gluon helicity operator in a non-local form [10,11],where ∇ + = ∂/∂ξ − . It is the gauge-invariant extension (GIE) of the operator E × A in the light-cone gauge A + = 0, but one cannot evaluate this expression on the lattice directly due to its real-time dependence.On the other hand,S g is equal to the infinite momentum frame (IMF) limit of a universality class of operators [12] whose matrix elements can be matched to ∆G through a factorization formula in large momentum effect...

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“…The central π 0 asymmetries at 200 [1] and 510 GeV [3] are displayed in Fig. 1 as a function of x T = p T / √ s. One clearly sees the increasingly nonzero asymmetries with increasing x T .…”

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“…Therefore, in principle the ordering of the three asymmetries directly shows the sign of the gluon helicity probed. PHENIX has measured all charges at 200 GeV [1,2] but due to trigger limitations the precision is not sufficient so far. At 510 GeV the charged pion analysis is ongoing while the neutral pion analysis will be discussed below.…”

Section: Introductionmentioning

confidence: 99%

Measurement of double helicity asymmetries ($A_{LL}$) at mid- and forward rapidities in longitudinally polarized $p+p$ collisions at $\sqrt{s}$ = 510 GeV with PHENIX experiment

Seidl¹,

Moon²

2016

Proceedings of XXIV International Workshop on Deep-Inelastic Scattering and Related Subjects — PoS(DIS2016)

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One of the main goals of the RHIC spin program as well as the PHENIX experiment is to determine the gluon spin contribution to the total spin of the nucleon. Recent longitudinally polarized proton-proton collision results at RHIC at a center-of-mass energy of 200 GeV have indicated a nonzero gluon spin contribution at x above 0.05. In recent years RHIC has been operating at a higher center-of-mass energy which allows to extend the covered range. PHENIX has published neutral pion asymmetries at central rapidities which clearly confirm the nonzero gluon contributions and extend the measured range to 0.01. Another measurement of J/ψ asymmetries at forward rapidities extends the sensitivity until 0.001.

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Inclusive double-helicity asymmetries in neutral-pion and eta-meson production inp→+p→collisions at<

Cited by 76 publications

References 52 publications

Nucleon Spin and Momentum Decomposition Using Lattice QCD Simulations

Nucleon Spin and Momentum Decomposition Using Lattice QCD Simulations

Glue Spin and Helicity in the Proton from Lattice QCD

Measurement of double helicity asymmetries ($A_{LL}$) at mid- and forward rapidities in longitudinally polarized $p+p$ collisions at $\sqrt{s}$ = 510 GeV with PHENIX experiment

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