Towards a unified picture of constituent and current quarks

Scopetta, Sergio; Vento, V.; Traini, M.

doi:10.1016/s0370-2693(97)01599-2

Cited by 48 publications

(92 citation statements)

References 34 publications

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“…The experimental parton distributions however, unveil the structure of the pion in terms of fundamental partons. How to relate the constituent quarks and the fundamental partons is an old problem analyzed by Altarelli, Cabibbo, Maiani and Petronzio [27], and applied more recently to the pion [30] and to the nucleon [28,29]. Let us recall the main features of this development.…”

Section: Experimental Analysis Of Pdfsmentioning

confidence: 99%

“…[28] for the proton case A = 0.435, B = 0.378, C = 0.05, D = 2.778, and G = 0.135, since these functions should in principle be independent of the hadron under scrutiny. Once the convolution defined by Altarelli et al is performed, we proceed to look for the evolution of the parton distribution under the Renormalization Group.…”

Section: Experimental Analysis Of Pdfsmentioning

confidence: 99%

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Pion parton distributions in a nonlocal Lagrangian

Noguera

Vento

2006

Eur. Phys. J. A

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We use phenomenological nonlocal Lagrangians, which lead to non trivial forms for the quark propagator, to describe the pion. We define a procedure based on previous studies on non local lagrangians for the calculation of the pion parton distributions at low Q 2 . The obtained parton distributions fulfill all the wishful properties. Using a convolution approach we incorporate the composite character of the constituent quarks. We evolve, using the Renormalization Group, the calculated parton distributions to the experimental scale and compare favorably with the data and draw conclusions.PACS numbers: 11.10. St, 12.38.Lg, 13.60.Fz, 24.10.Jv I. INTRODUCTIONParton Distributions Functions (PDFs) and Generalized Parton Distributions (GPDs) [1,2,3], relating PDFs and electromagnetic form factors, encode unique information on the non perturbative hadron structure (for a recent review, see [4]). Any realistic model of hadron structure should be able to calculate them. We shall proceed in here to study the parton distribution functions of the pion in a previous developed formalism [5].From the experimental point of view the PDFs and GPDs of the pion are difficult to determine. Pions decay into muons or photons and therefore the pion distribution functions can not be obtained from direct DIS experiments. The pion parton distribution has been inferred from the Drell-Yang process [6,7,8] and direct photon production [9] in pion-nucleon and pion-nucleus collisions. These set of experiments have been analyzed in ref. [10] obtaining that the fraction of moment of each valence (anti)quark in the pion is about 0.23 for Q 2 = 4 GeV 2 . The parton distribution functions of the pion has been a subject of much discussion in the literature. In [11,12] calculations using quenched lattice QCD, for their lowest moments, were performed. The lack of sea quarks in the approximation implies a greater presence of valence quarks. Its PDFs [13,15] and GPDs [16] have been also calculated in the Nambu-Jona Lasinio (NJL) model [17]. In the chiral limit, its quark valence distribution is as simple as q (x) = θ (x) θ (1 − x) . Once evolution is taken into account, good agreement is reached between the calculated PDFs and the experimental results [13]. The pion PDFs and GPDs have also been calculated in a model with the simplest pseudoscalar coupling between the pion and the constituent quark fields [14], and in the instanton model, [19,20]. In ref.[19] the chiral limit result of the NJL model for PDFs changes such that q (x) goes to zero for x → 0 and x → 1. The pion PDFs have also been calculated in a spectral quark model [18]. Also, the pion PDFs have been calculated in a statistical model, without any dynamical assumption, obtaining quite reasonable results [21] . In [22] the GPDs of the pion are calculated in the bag model. A relevant contribution to the calculation of the pion GPDs on the light-front has been given by Tiburzi and Miller [23], and some remarks on the use of the light-front for calculating GPDs can be found in [24]. Looking f...

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Section: Experimental Analysis Of Pdfsmentioning

confidence: 99%

Section: Experimental Analysis Of Pdfsmentioning

confidence: 99%

Pion parton distributions in a nonlocal Lagrangian

Noguera

Vento

2006

Eur. Phys. J. A

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“…[ 11], convoluted with the GPDS of the constituent quarks themselves. The latter are modeled by using the structure functions of the constituent quark, obtained generalizing to the GPDs case the approach of [ 12] which is, in turn, built following the idea of Ref [ 13], the double distribution representation on GPDs (see, i.e., [ 2,14]), and a recently proposed phenomenological constituent quark form factor [ 15]. Results have been discussed in Ref.…”

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confidence: 99%

Generalized parton distributions of hadrons with composite constituents

Scopetta¹

2007

Nuclear Physics A

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A method is described for calculating the Generalized Parton Distributions (GPDs) of spin 1/2 hadrons made of composite constituents, in an Impulse Approximation framework. GPDs are obtained from the convolution between the light cone non-diagonal momentum distribution of the hadron and the GPD of the constituent. DIS structure functions and electromagnetic form factors are consistently recovered with the proposed formalism. Results are presented for the nucleon and for the 3 He nucleus. For a nucleon assumed to be made of composite constituent quarks, the proposed scheme permits to study the so-called Efremov-Radyushkin-Brodsky-Lepage (ERBL) region, difficult to access in model calculations. Results are presented for both helicity-independent and helicity-dependent GPDs. For 3 He, the calculation has been performed by evaluating a non-diagonal spectral function within the AV18 interaction. It turns out that a measurement of GPDs for 3 He could shed new light on the short-range nuclear structure at the quark level.Generalized Parton Distributions (GPDs) [ 1] represent one of the most relevant issues in nowadays hadronic Physics (for recent reviews, see, e.g., Ref.[ 2]). GPDs parameterize the long-distance dominated part of exclusive lepton Deep Inelastic Scattering (DIS) off hadrons and can be measured in Deeply Virtual Compton Scattering (DVCS), i.e. the process eH −→ e ′ H ′ γ when Q 2 ≫ m 2 H , permits to access GPDs (here and in the following, Q 2 is the momentum transfer between the leptons e and e ′ , and ∆ 2 the one between the hadrons H and H ′ ) so that relevant experimental DVCS programs are taking place. The issue of measuring GPDs for nuclei is also being addressed [ 3], following an observation firstly discussed in [ 4]. As a mater of facts, the knowledge of GPDs would permit the study of the short light-like distance structure of nuclei, and thus the interplay of nucleon and parton degrees of freedom in the nuclear wave function. In DIS off a nucleus with four-momentum P A and A nucleons of mass M, this information can be accessed in the region where Ax Bj ≃ Q 2 /(2Mν) > 1, being x Bj = Q 2 /(2P A · q) and ν the energy transfer in the laboratory system. In this kinematical region measurements are difficult, because of the vanishing of the cross-sections. As explained in Ref. [ 4], the same physics can be accessed in DVCS at lower values of x Bj , as it will be clear later [ 5].In this talk, a method is reviewed for calculating the GPDs of spin 1/2 hadrons made of composite constituents, in an Impulse Approximation (IA) framework. In this scheme, GPDs are given by the convolution between the light cone non-diagonal momentum distribution of the hadron and the GPD of the constituent. Results are presented for the

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“…We h a v e developed an approach which uses model calculations for the latter ingredients [1]. Moreover, in order to relate the constituent quark with the current partons of the theory, a procedure, hereafter called ACMP, has been applied [2,3]. Within this approach, constituent Supported in part by DGICYT-PB94-0080 and TMR programme of the European Commission ERB FMRX-CT96-008; based on two talks given at: 1) Workshop \N Physics and non perturbative QCD", Trento, Italy, M a y 18-29 1998, to be published in Few Body Systems, Suppl.…”

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confidence: 99%

“…In our picture the constituent quarks are themselves complex objects whose structure functions are described by a set of functions ab that specify the numb e r o f p o i n t-like partons of type b, which are present in the constituents of type a with fraction x of its total momentum [2,3]. In general a and b specify all the relevant quantum numbers of the partons, i.e., avor and spin.…”

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confidence: 99%

Nucleon Structure Functions in a Constituent Quark Scenario

Scopetta

Vento

Traini

1999

Few-Body Problems in Physics ’98

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Abstract. Using a simple picture of the constituent quark as a composite system of point-like partons, we construct the polarized parton distributions by a convolution between constituent quark momentum distributions and constituent quark structure functions. We achieve good agreement with experiments in the unpolarized as well as in the polarized case, though a good description of the recent polarized neutron data requires the introduction of one more parameter. When our results are compared with similar calculations using non-composite constituent quarks, the accord with the experiments of the present s c heme is impressive. We conclude that DIS data are consistent with a low energy scenario dominated by composite constituents of the nucleon.At l o w energies, the so called naive quark model accounts for a large number of experimental observations. At large energies, QCD sets the framework for an understanding of the Deep Inelastic Scattering (DIS) phenomena beyond the Parton Model. However, the perturbative approach t o QCD does not provide absolute values for the observables. The description based on the Operator Product Expansion (OPE) and the QCD evolution requires the input of non-perturbative matrix elements. We h a v e developed an approach which uses model calculations for the latter ingredients [1]. Moreover, in order to relate the constituent quark with the current partons of the theory, a procedure, hereafter called ACMP, has been applied [2,3]. Within this approach, constituent Supported in part by DGICYT-PB94-0080 and TMR programme of the European Commission ERB FMRX-CT96-008; based on two talks given at: 1) Workshop \N Physics and non perturbative QCD", Trento, Italy, M a y 18-29 1998, to be published in Few Body Systems, Suppl.; 2) Conference \Fev Body 16 th ", Autrans, France, June 1-6, 1998, to be published in Few Body Systems, Suppl.

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Towards a unified picture of constituent and current quarks

Cited by 48 publications

References 34 publications

Pion parton distributions in a nonlocal Lagrangian

Pion parton distributions in a nonlocal Lagrangian

Generalized parton distributions of hadrons with composite constituents

Nucleon Structure Functions in a Constituent Quark Scenario

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