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K, Abe; Akagi, T.; Anthony, P.L.; Antonov, R.; Arnold, R. G.; Averett, T.; Band, H. R.; Bauer, J. M.; Borel, H.; Bosted, P.; Breton, Vincent; Button‐Shafer, J.; Chen, J. P.; Chupp, T. E.; Clendenin, J. E.; Comptour, C.; Coulter, K. P.; Court, G.R.; Crabb, D.; Daoudi, M.; Day, D.; Dietrich, F. S.; Dunne, J.; Dutz, H.; Erbacher, R.; Fellbaum, J.; Feltham, A.; Fonvieille, H.; Frlež, E.; Garvey, D.; Gearhart, R.; Gómez, J.; Greniér, Philippe; Griffioen, K. A.; Høibråten, S.; Hughes, E. W.; Hyde‐Wright, C. E.; Johnson, J. R.; Kawall, D.; Klein, A.; Kuhn, S. E.; Kuriki, M.; Lindgren, R.; Liu, T. J.; Lombard-Nelsen, R. M.; Marroncle, J.; Maruyama, T.; Maruyama, X. K.; McCarthy, J.; Meyer, W.; Meziani, Z. E.; Minehart, R.; Mitchell, J.; Morgenstern, J.; Petratos, G. G.; Pitthan, R.; Počanić, D.; Prescott, C.Y.; Prepost, R.; Raines, P.; Raue, B. A.; Reyna, D.; Rijllart, A.; Roblin, Y.; Rochester, L.S.; Rock, S. E.; Rondon, O.; Sick, I.; Smith, L. C.; Smith, T. B.; Spengos, M.; Staley, F.; Steiner, P.; Lorant, S. St.; Stuart, L. M.; Suekane, F.; Szalata, Z. M.; Tang, Huan; Terrien, Y.; Usher, T.; Walz, D.; White, J. L.; Witte, K.; Young, C.; Youngman, B.; Yuta, H.; Zapalac, G.; Zihlmann, B.; Zimmermann, D.

doi:10.1103/physrevlett.74.346

Cited by 313 publications

(123 citation statements)

References 33 publications

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“…The blue data points are from Jlab [190], the green points are from Hermes [183], the black points are from Fermilab [78], the red points are from CERN [186] and the magenta points are from SLAC [179,181,182,184].…”

Section: Effective Chargesmentioning

confidence: 99%

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The QCD running coupling

Deur

Brodsky

Téramond

2016

Progress in Particle and Nuclear Physics

312

236

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We review the present theoretical and empirical knowledge for α s , the fundamental coupling underlying the interactions of quarks and gluons in Quantum Chromodynamics (QCD). The dependence of α s (Q 2 ) on momentum transfer Q encodes the underlying dynamics of hadron physics -from color confinement in the infrared domain to asymptotic freedom at short distances. We review constraints on α s (Q 2 ) at high Q 2 , as predicted by perturbative QCD, and its analytic behavior at small Q 2 , based on models of nonperturbative dynamics. In the introductory part of this review, we explain the phenomenological meaning of the coupling, the reason for its running, and the challenges facing a complete understanding of its analytic behavior in the infrared domain.In the second, more technical, part of the review, we discuss the behavior of α s (Q 2 ) in the high momentum transfer domain of QCD. We review how α s is defined, including its renormalization scheme dependence, the definition of its renormalization scale, the utility of effective charges, as well as "Commensurate Scale Relations" which connect the various definitions of the QCD coupling without renormalization-scale ambiguity. We also report recent significant measurements and advanced theoretical analyses which have led to precise QCD predictions at high energy. As an example of an important optimization procedure, we discuss the "Principle of Maximum Conformality", which enhances QCD's predictive power by removing the dependence of the predictions for physical observables on the choice of theoretical conventions such as the renormalization scheme. In the last part of the review, we discuss the challenge of understanding the analytic behavior α s (Q 2 ) in the low momentum transfer domain. We survey various theoretical models for the nonperturbative strongly coupled regime, such as the light-front holographic approach to QCD. This new framework predicts the form of the quark-confinement potential underlying hadron spectroscopy and dynamics, and it gives a remarkable connection between the perturbative QCD scale Λ and hadron masses. One can also identify a specific scale Q 0 which demarcates the division between perturbative and nonperturbative QCD. We also review other important methods for computing the QCD coupling, including lattice QCD, the Schwinger-Dyson equations and the GribovZwanziger analysis. After describing these approaches and enumerating their conflicting predictions, we discuss the origin of these discrepancies and how to remedy them. Our aim is not only to review the advances in this difficult area, but also to suggest what could be an optimal definition of α s (Q 2 ) in order to bring better unity to the subject.2

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Section: Effective Chargesmentioning

confidence: 99%

“…4.1 by the dashed red line. The range between the low and high Q 2 constraints is densely filled by experimental data [190], mostly coming from the Bjorken integral data [75,179,180,181,182,183,184,185,186]. Other data come from the CCFR measurement [78] of the Gross-Llewellyn Smith sum rule [74], Eq.…”

Section: Effective Chargesmentioning

confidence: 99%

The QCD running coupling

Deur

Brodsky

Téramond

2016

Progress in Particle and Nuclear Physics

312

236

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“…The experimental results reported in [2][3][4] suggest that the gluon spin and orbital interaction contribute significantly to the proton spin. Naturally, these experimental results require a theoretical explanation.…”

Section: Introductionmentioning

confidence: 91%

Contribution of superstring Z′ boson on the polarization effects in proton proton collisions

Muradov

Ahmadov

2005

Open Physics

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In this work we investigate the single-and the double-spin asymmetries at the collisions of polarized protons pp → (γ * , Z 0 , Z ′ ) + X within the scope of QCD, the electroweak interaction and superstring E 6 theory. The helicity amplitude method is used. Analytical expressions for the single-and the double-spin asymmetries are obtained and their dependence on the transverse momentum of the lepton pair is investigated at the three different values of invariant masses of the lepton pair. The pure contribution coming from the superstring Z ′ boson on the single-and double-spin asymmetries has been extracted. The results obtained allow investigation of the spin structure of the proton.

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“…In the naive quark parton model, the quarks are 'free' and the spin of a nucleon can be considered as arising from the spin of its quarks, 29) where only the three lightest quarks have been considered . It is helpful to examine the SU(3) flavor combinations:…”

Section: The Quark Parton Modelmentioning

confidence: 99%

“…SMC was run at CERN in 1993 [24,25,261, E142 was run at SLAC in 1993 [27, 281, and E143 was run at SLAC in 1994 [29,301. The experiments at CERN were at a higher energy and able to reach a lower x, while the experiments at SLAC collected significantly more data and have much smaller statistical errors.…”

Section: 5mentioning

confidence: 99%

A Precision Measurement of the Neutron Spin Structure Functions Using a Polarized HE-3 Target

Smith¹

2003

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This thesis describes a precision measurement of the neutron spin dependent structure function, g r ( x ) . The measurement was made by the E154 collaboration at SLAC using a longitudinally polarized, 48.3 GeV electron beam, and a 3He target polarized by spin exchange with optically pumped rubidium. A target polarization as high as 50% was achieved. The elements of the experiment which pertain to the polarized 3He target will be described in detail in this thesis. To achieve a precision measurement, it has been necessary to minimize the systematic error from the uncertainty in the target parameters. All of the parameters of the target have been carefully measured, and the most important parameters of the target have been measured using multiple techniques. The polarization of the target was measured using nuclear magnetic resonance techniques, and has been calibrated using both proton NMR and by measuring the shift of the Rb Zeeman resonance frequency due t o the 3He polarization. The fraction of events which originated in the 3He, as measured by the spectrometers, has been determined using a physical model of the target and the spectrometers. It was also measured during the experiment using a variable pressure 3He reference cell in place of the polarized 3He target. " .The spin dependent structure function g;"(z) was measured in the Bjorken 2 range of 0.014 < 2 < 0.7 with an average Q2 of 5 (GeV/c)2. One of the primary motivations for this experiment was t o test the Bjorken sum rule. Because the experiment had smaller statistical errors and a broader kinematic coverage than previous experiments, the behavior of the spin structure function g;(z) could be studied in detail at low values of the Bjorken scaling variable 5 . It was found that g;"(x) has a strongly divergent behavior at low values of 2, calling into question the methods commonly used t o extrapolate the value of g;(z) t o low 2. The precision of the measurement made by the E154 collaboration at SLAC puts a tighter constraint on the extrapolation of g;"(x) t o low 2, which is necessary t o evaluate the Bjorken sum rule.T . ACKNOWLEDGEMENTS

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Precision Measurement of the Proton Spin Structure Functiong1p

Cited by 313 publications

References 33 publications

The QCD running coupling

The QCD running coupling

Contribution of superstring Z′ boson on the polarization effects in proton proton collisions

A Precision Measurement of the Neutron Spin Structure Functions Using a Polarized HE-3 Target

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