Spin Dependence of High-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>P</mml:mi></mml:mrow><mml:mrow><mml:mi>⊥</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>Elastic<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>p</mml:mi><mml:mo>−</mml:mo><mml:mi>p</mml:mi></mml:math>Scattering

Crabb, D.; Fernow, R.; Hansen, P. H.; Krisch, A. D.; Salthouse, A. J.; Sandler, B.; Terwilliger, K. M.; O’Fallon, J. R.; Crosbie, E.; Ratner, L. G.; Schultz, P. F.

doi:10.1103/physrevlett.41.1257

Cited by 135 publications

(38 citation statements)

References 14 publications

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“…The ratio of (dσ/dt) ↑↑ /(dσ/dt) ↑↓ with spin normal to the scattering plane can reach 4 at θ cm = 90 • [14]; the differential cross section dσ/dt oscillates around the scaling value [15]. The interference between the short-distance and long-distance (Landshoff) subprocesses due to soft gluon radiation [16] can explain the above spin-spin correlation and oscillatory scaling behavior [17,18].…”

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confidence: 95%

Cross-Section Measurement of Charged-Pion Photoproduction from Hydrogen and Deuterium

Zhu¹,

Arrington²,

Averett³

et al. 2003

Phys. Rev. Lett.

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We have measured the differential cross section for the γn → π − p and γp → π + n reactions at θcm = 90 • in the photon energy range from 1.1 to 5.5 GeV at Jefferson Lab (JLab). The data at Eγ 3.3 GeV exhibit a global scaling behavior for both π − and π + photoproduction, consistent with the constituent counting rule and the existing π + photoproduction data. Possible oscillations around the scaling value are suggested by these new data. The data show enhancement in the scaled cross section at a center-of-mass energy near 2.2 GeV. The cross section ratio of exclusive π − to π + photoproduction at high energy is consistent with the prediction based on one-hard-gluon-exchange diagrams.PACS numbers: 13.60. Le, 24.85.+p, 25.10.+s, The study of the transition region from nucleon-meson degrees of freedom to quark-gluon degrees of freedom in quantum chromodynamics (QCD) for exclusive processes is one of the most interesting subjects in nuclear physics. Scaling in the differential cross section dσ/dt, and hadron helicity conservation have been pursued experimentally as signatures of this transition for years. While global scaling behavior has been observed in many exclusive processes, no experimental evidence supports hadron helicity conservation. Furthermore, the exact nature governing the onset of the scaling behavior is not clear. The relatively large cross section of pion photoproduction allows the search for additional possible signatures: QCD oscillations and the charged pion cross section ratio. In this experiment, three signatures (scaling, QCD oscillations, charged pion ratio) for the transition are investigated.For an exclusive two-body reaction AB → CD at high energy and large momentum transfer, the constituent counting rule (or the dimensional scaling law) predicts [1]where s and t are the Mandelstam variables. The quantity n is the total number of interacting elementary fields in the reaction, and f (θ cm ) is the angular dependence of the differential cross section. This rule was originally derived from dimensional analysis [1], and later confirmed within the framework of a perturbative QCD (pQCD) analysis up to a logarithmic factor of the strong coupling constant α s [2]. Many exclusive measurements at

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confidence: 95%

Cross-Section Measurement of Charged-Pion Photoproduction from Hydrogen and Deuterium

Zhu¹,

Arrington²,

Averett³

et al. 2003

Phys. Rev. Lett.

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“…Oscillations are not restricted to the pp elastic scattering channel; they are seen in elastic πp fixed angle scattering [14] and hints of oscillation about the s −7 scaling have also been reported in the recent data [5] from Jefferson Lab (JLab) on photo-pion production above the resonance region. In addition to violations of the scaling laws, spin correlations in polarized pp elastic scattering also show significant deviations from perturbative QCD (pQCD) expectations [15,16]. Several sets of arguments have been put forward to account for these deviations from scaling laws and the unexpected spin correlations.…”

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confidence: 99%

Generalized counting rule and oscillatory scaling

Dutta

Gao

2005

Phys. Rev. C

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We have studied the energy dependence of the pp elastic scattering data and the pionphotoproduction data at 90• c.m. angle in light of the new generalized counting rule derived for exclusive processes. We show that by including the helicity-nonconserving amplitudes and their interference with the Landshoff amplitude, we are able to reproduce the energy dependence of all the pp elastic cross-section and spin-correlation (ANN ) data available above the resonance region. The pion-photoproduction data can also be described by this approach, however, data with much finer energy spacing is needed to confirm the oscillations about the scaling behavior. This study strongly suggests an important role for helicity-nonconserving amplitudes related to quark orbital angular momentum and for the interference of these amplitudes with the Landshoff amplitude at GeV energies.PACS numbers: 13.75. Cs, 24.85.+p, 25.10.+s, The transition between perturbative and nonperturbative regimes of Quantum Chromo Dynamics (QCD) is of long-standing interest in nuclear and particle physics. Exclusive processes play a central role in studies trying to map out this transition. The differential cross sections for many exclusive reactions [1] at high energies and large momentum transfers appear to obey dimensional scaling laws [2] (also called quark counting rules). In recent years, the onset of this scaling behavior has been observed at a hadron transverse momentum of ∼ 1.2 (GeV/c) in deuteron photo-disintegration [3,4] and in pion photoproduction from nucleon [5]. On the other hand, these models also predict hadron helicity conservation in exclusive processes [6], and experimental data in similar energy and momentum regions tend not to agree with these helicity conservation selection rules [7]. Although contributions from non-zero parton orbital angular momenta are power suppressed, as shown by Lepage and Brodsky [8], they could break hadron helicity conservation rule [9]. Interestingly recent re-analysis of quark orbital angular momenta seems to contradict the notion of power suppression [10]. Furthermore, Ref [11] argues that non-perturbative processes could still be important in some kinematic regions even at high energies. Thus the transition between the perturbative and nonperturbative regimes remains obscure and makes it essential to understand the exact mechanism governing the early onset of scaling behavior.Towards this goal, it is important to look closely at claims of agreement between the differential cross section data and the quark counting rule prediction. Deviations from the quark counting rules have been found in exclusive reactions such as elastic proton-proton (pp) scattering [12,13]. In fact, the re-scaled 90• center-ofmass pp elastic scattering data, s 10 dσ dt show substantial oscillations about the power law behavior. Oscillations are not restricted to the pp elastic scattering channel; they are seen in elastic πp fixed angle scattering [14] and hints of oscillation about the s −7 scaling have also been reported in the recen...

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“…With the advent of QCD, the current wisdom based on perturbative contributions was that spin effects should generally be small as energy increases. However, a measurement by Krisch et al [107][108][109], indicated a large value of the spin-spin correlation A nn at 90…”

Section: Proton-proton Scattering and Other Similar Reactionsmentioning

confidence: 99%

“…This striking result of [107][108][109] motivated interesting studies on the underlying mechanisms. See, e.g., [65].…”

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confidence: 99%

Spin observables and spin structure functions: Inequalities and dynamics

et al. 2009

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Model-independent identities and inequalities which relate the various spin observables of collisions in nuclear and particle physics are reviewed in a unified formalism. Their physical interpretation and their implications for dynamical models are also discussed. These constraints between observables can be obtained in several ways: from the explicit expression of the observables in terms of a set of helicity or transversity amplitudes, a non-trivial algebraic exercise which can be preceded by numerical simulation with randomly chosen amplitudes, from anticommutation relations, or from the requirement that any polarisation vector is less than unity. The most powerful tool is the positivity of the density matrices describing the spins in the initial or final state of the reaction or its crossed channels. The inequalities resulting from positivity need to be projected to single out correlations between two or three observables. The quantum aspects of the information carried by spins, in particular entanglement, are considered when deriving and discussing the constraints Several examples are given, with a comparison with experimental data in some cases. For the exclusive reactions, the cases of the strangeness-exchange proton-antiproton scattering and the photoproduction of pseudoscalar mesons are treated in some detail: all triples of observables are constrained, and new results are presented for the allowed domains. The positivity constraints for total cross-sections and for the simplest observables of single-particle inclusive reactions are reviewed. They also apply to spin-dependent structure functions and parton distributions, both integrated or transverse-momentum dependent. The corresponding inequalities are shown to be preserved by the evolution equations of quantum chromodynamics.Inequalities on spin observables 3

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Spin Dependence of High-P⊥2Elasticp−pScattering

Cited by 135 publications

References 14 publications

Cross-Section Measurement of Charged-Pion Photoproduction from Hydrogen and Deuterium

Cross-Section Measurement of Charged-Pion Photoproduction from Hydrogen and Deuterium

Generalized counting rule and oscillatory scaling

Spin observables and spin structure functions: Inequalities and dynamics

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