Importance of Lorentz structure in the parton model: Target mass corrections, transverse momentum dependence, positivity bounds (original) (raw)
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A new combined next to leading order QCD analysis of the polarized inclusive and semi-inclusive deep inelastic lepton-hadron scattering (DIS) data is presented. In contrast to previous combined analyses, the 1/Q2 terms (kinematic—target mass corrections, and dynamic—higher twist corrections) in the expression for the nucleon spin structure function g1 are taken into account. The new COMPASS data are included in the analysis. The impact of the semi-inclusive data on the polarized parton densities (PDFs) and on the higher twist corrections is discussed. The new results for the PDFs are compared to our (Leader, Sidorov, Stamenov) LSS’06 PDFs, obtained from the fit to the inclusive DIS data alone, and to those obtained from the de Florian, Sassot, Stratmann, and Vogelsang global analysis.
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International Journal of Modern Physics A, 2014
This is a review of the program we started in 1968 to understand and generalize Bjorken scaling and Feynman's parton model in a canonical quantum field theory. It is shown that the parton model proposed for deep inelastic electron scatterings can be derived if a transverse momentum cutoff is imposed on all particles in the theory so that the impulse approximation holds. The deep inelastic electron-positron annihilation into a nucleon plus anything else is related by the crossing symmetry of quantum field theory to the deep inelastic electron-nucleon scattering. We have investigated the implication of crossing symmetry and found that the structure functions satisfy a scaling behavior analogous to the Bjorken limit for deep inelastic electron scattering. We then find that massive lepton pair production in collisions of two high energy hadrons can be treated by the parton model with an interesting scaling behavior for the differential cross sections. This turns out to be the first example of a class of hard processes involving two initial hadrons.
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Large-Momentum Effective Theory (or LaMET) advocated by the present authors provides a direct approach to simulate parton physics in Euclidean lattice QCD theory. Recently, there has been much interest in this theory in the literature, with some questioning its validity and effectiveness. Here we provide some discussions aiming at a further exposition of this approach. In particular, we explain why it does not have the usual power divergence problem in lattice QCD calculations for the moments of parton distributions. The only power divergence in the LaMET approach comes from the self-energy of the Wilson lines which can be properly factorized. We show that although the Ioffe-time distribution provides an alternative way to extract the parton distribution from the same lattice observables, it also requires the same large momentum (or short distance) limit as in LaMET to obtain a precision calculation. With a proper quantification of errors, both extraction methods shall be compared with the same lattice data.
Arxiv preprint arXiv:1106.1145, 2011
Unintegrated parton density functions (uPDFs) of Quantum Chromodynamics (QCD), also known as TMDPDFs, are generally used to study details of hadronic final states in high energy lepton-hadron and hadron-hadron collisions; while the integrated parton density functions (PDFs) are used for conventional deep inelastic inclusive processes. The self-similarity based Model of proton structure function F 2 (x, Q 2) suggested in recent years are however based on specific uPDFs with self-similarity at small x. In this work, we study large x limit of such a Model and modify the defining uPDFs to make them compatible with theoretical expectations in such limit. Possibility of saturation of Froissart bound in this Model is discussed. We also reanalyze the PDFs in this approach using its conventional relation with TMDPDFs.
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Zeitschrift für Physik C Particles and Fields, 1988
We give several sets of parton densities derived from recent measurements of structure functions in deep inelastic scattering. The difference among these densities reflects the uncertainties from deep inelastic data of different experiments, allowing an estimate of the error band for the predictions one may obtain for any given hadronic process at higher energy. The densities are available at any scale Q2< 5.109GeV 2 and x>5.10 -5 and include next-toleading corrections as well as threshold effects due to heavy flavours. A comparison with a large set of data in a wide range of scales (Drell-Yan, W and Z production, etc.) is also presented.
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Deep-inelastic one-particle inclusive processes in the parton model
Nuclear Physics B, 1973
We study the processes e + N ~ e' + h + anything, e + + e-~ h + anything, within the parton model of Landshoff, Polkmghorne and Short Defimte and pecuhar predletlons are obtained, also common to the Drell, Levy and Yah cutoff theory and to the h~ 3 ladder model. These predictions can be summarized as follows 0) m the photon fragmentation region the cross section factorizes after integration over transverse momentum of h, (n) m the target fragmentaUon region Regge behavlour, vahd at large to, gwes rise to double Regge exchange for small values of the Feynman variable y, but only up to y ~-l/to, (m) the structure functions vamsh at y = 0, 0v) total multiplicities in the first process mcrease hke In to for large to, and m the second reach a fmlte limit at large q~ In the case where only one SU(3) multlplet of partons is present (as m the quark parton model) umque relations, vahd m the ltmlt of exact SU(3), are found between the cross section and multipheltles m the first process and the analogous quantities for the forward reglon of the second process * For sanphclty of notation we shall suppress the dependence upon the pamcular ha&on h m all of the structure functions that we introduce
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Physical Review D, 1972
We discuss the phenomenological consequences of parton models for photon processes. In particular, the "breakdown" of vector meson dominance in Compton scattering is correlated with its failure in nuclear photoabsorption by showing that the parton model gives rise to a nonshadowed pointlike contribution which occurs only in two-photon processes. Included in this contribution is a piece which corresponds in the general Compton amplitude T PV to a term which is independent of energy and photon masses at fixed t. It is emphasized that failure to observe a contribution with such behavior would have profound consequences for conventional parton models. We predict that this contribution will have only a weak t dependence and will lead to a dominantly real spin conserving amplitude at large t values for Compton scattering. The q2 behavior of this fixed pole is most easily detected in wide angle bremsstrahlung experiments, though the same mechanism will also give rise to an s-wave enhancement independent of the photon masses in ee ee 7r7r.