Evolution of the nucleon structure in the lightest nuclei (original) (raw)
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Structure functions of bound nucleons: From the EMC effect to nuclear shadowing
Zeitschrift f�r Physik C Particles and Fields, 1993
We describe the nuclear structure functions in the whole range of the Bjorken variable x, by combining various effects in a many-step procedure. First, we present a QCD motivated model of nucleons, treated, in the limit of vanishing Q2, as bound states of three relativistic constituent quarks. Gluons and sea quarks are generated radiatively from the input valence quarks. All parton distributions are described in terms of the confinement (or nucleon's) radius. The results for free nucleons are in agreement with the experimental determinations. The structure functions of bound nucleons are calculated by assuming that the main effect of nucleon binding is stretching of nucleons. The larger size of bound nucleons lowers the valence momentum and enhances the radiatively generated glue and sea densities. In the small-x region the competitive mechanism of nuclear shadowing takes place. It also depends on the size of the nucleons. By combining stretching, shadowing and Fermi motion effects (the latter confined to very large x), the structure function ratio is well reproduced. Results are also presented for the A-dependence of the momentum integral of charged partons, the nuclear gluon distribution and the hadron-nuelei cross sections.
The Dynamical Origin of Nuclear Mass Number Dependence in EMC-Effect
Progress of Theoretical Physics, 1986
A new method to extract the absolute probability of the exotic component in the nucleon structure function of the deep inelastic lepton• nucleus scattering is proposed. Then it is found that the mass number dependence of the probability determined is consistent with the probability of exotic components in multi•nucleon overlap. This suggests that the deformation of the nucleon structure function is caused by the interaction among nucleons during their overlap.
Measurement of the nucleon structure function in the nuclear medium and evaluation of its moments
Nuclear Physics A, 2010
We report on the measurement of inclusive electron scattering off a carbon target performed with CLAS at Jefferson Laboratory. A combination of three different beam energies 1.161, 2.261 and 4.461 GeV allowed us to reach an invariant mass of the final-state hadronic system W ≈ 2.4 GeV with four-momentum transfers Q 2 ranging from 0.2 to 5 (GeV/c) 2 . These data, together with previous measurements of the inclusive electron scattering off proton and deuteron, which cover a similar continuous two-dimensional region of Q 2 and Bjorken variable x, permit the study of nuclear modifications of the nucleon structure. By using these, as well as other world data, we evaluated the F 2 structure function and its moments. Using an OPE-based twist expansion, we studied the Q 2 -evolution of the moments, obtaining a separation of the leading-twist and the total higher-twist terms. The carbon-to-deuteron ratio of the leading-twist contributions to the F 2 moments exhibits the well-known EMC effect, compatible with that discovered previously in x-space. The total higher-twist term in the carbon nucleus appears, although with large systematic uncertainties, to be smaller with respect to the deuteron case for n < 7, suggesting partial parton deconfinement in nuclear matter. We speculate that the spatial extension of the nucleon is changed when it is immersed in the nuclear medium.
A QCD-based explanation for changes in nucleon properties in nuclei
Physics Letters B, 1988
it is inferred from QCD sum rules that f~, g~NN and A decrease with nuclear matter density, leading to an increase of the nucleon radius but little change in its magnetic moment. All model dependent calculations in heavier nuclei should take these changes into account.
Structure of proton and nuclei
Arxiv preprint hep-ph/9407210, 1994
We discuss in this set of lectures the structure of proton/neutron as revealed through a study of form-factors. This is followed by a discussion of the structure functions of proton/nuclear targets as measured in the deep inelastic scattering (DIS) of leptons off these targets. We discuss the parton model in DIS as well as outline the usage of parton model in processes other than the DIS. We then go on to dicsuss the EMC effect: the nuclear dependence of the structure functions. After a discussion of different models of the EMC effect we end by pointing out the possibility of distinguishing between these different models by studying the correlation between the A-dependence of different hard processes and the EMC effect.
A new approach to physics of nuclei
Physics of Atomic Nuclei, 2012
We employ the QCD sum rules method for description of nucleons in nuclear matter. We show that this approach provides a consistent formalism for solving various problems of nuclear physics. Such nucleon characteristics as the Dirac effective mass m * and the vector self-energy Σ V are expressed in terms of the in-medium values of QCD condensates. The values of these parameters at saturation density and the dependence on the baryon density and on the neutron-to-proton density ratio is in agreement with the results, obtained by conventional nuclear physics method. The contributions to m * and Σ V are related to observables and do not require phenomenological parameters. The scalar interaction is shown to be determined by the pion-nucleon σ-term. The nonlinear behavior of the scalar condensate may appear to provide a possible mechanism of the saturation. The approach provided reasonable results for renormalization of the axial coupling constant, for the contribution of the strong interactions to the neutron-proton mass difference and for the behavior of the structure functions of the in-medium nucleon. The approach enables to solve the problems which are difficult or unaccessible for conventional nuclear physics methods. The method provides guide-lines for building the nuclear forces. The threebody interactions emerge within the method in a natural way. There rigorous calculation will be possible in framework of self-consistent calculation in nuclear matter of the scalar condensate and of the nucleon effective mass m * .
Physical Review C, 2019
By using the valence quark exchange model, the up-and down-quark distribution functions as the distributions of three constituent quark inside the bound nucleons have been extracted and will be used in the context of the Altarelli, Cabibbo, Maiani, and Petronzio (ACMP) constituent quark model formalism to calculate the different pointlike parton distribution functions of the bound nucleons and the structure functions of 3 He and 3 H mirror nuclei at the energy scale of Q 2 = 4 GeV 2. In the latter picture the constituent quarks are assumed to be complex objects, made of pointlike partons which can be pointlike valence quarks, pointlike sea quarks, and pointlike neutral gluons. The sea quark and the gluon contributions to the structure functions of the helium-3 and the tritium nuclei have been analyzed in this scale of energy by reparameterizing the ACMP constituent quark model formalism. Unlike our previous works, where the parton densities inside the nucleon have been computed at the hadronic scale of energy, i.e., Q 2 0 = 0.34 GeV 2 , and then those distributions have been evolved to the high-energy scales by using the Dokshitzer, Gribove, Lipatov, Altarelli, and Parisi evolution equations, in the present study the parton distribution functions have been calculated at the energy scale of Q 2 = 4 GeV 2 directly by using the new parameters in the context of the dressed-quark scenario. Thus, at the first step, the extracted partonic distributions have been considered to calculate the nucleons and the nuclei structure functions and then the ratios of the neutron to the proton and 3 He to 3 H nuclei structure functions as well as the European Muon Collaboration ratios for the valence quark distributions, 3 He and 3 H nuclei, are calculated. The results are in a good agreement with both theoretical and available experimental data.
Nucleon parton distributions and nuclear structure
Nuclear Physics A, 1991
' ' ••^.T he current experimental status of measurements of nucleon structure funcSid' fi.' S.vind eep inelastic lepton scattering is presented. Recent BCDMS and SLAG results provide " " •-.. a consistent data set for charged lepton scattering. New probes of parton distributions: direct photons, Drell Yan di-muon production, W, Z and heavy quark production are providing information on the gluon and antiquark distributions. The implications of these data on our understanding of the structure of the nucleon, and the structure of the nucleon in the nucleus are discussed.
The evolution of nuclear structure: the scheme and related correlations
Journal of Physics G: Nuclear and Particle Physics, 1996
The evolution of collective nuclear structure is discussed from a horizontal perspective, that is, as a function of the number of valence protons and neutrons. Starting from an explicit recognition of the importance of the valence residual p-n interaction in the equilibrium shape and structure of nuclei, the phenomenological N p N n scheme is presented, and validated via an analysis of empirical p-n interaction strengths. Applications of the N p N n scheme are presented which exploit this paradigm of structural evolution. The physics underlying occasional deviations from the N p N n scheme is extracted and new signatures of structure and of nuclear shape components are developed which will be useful for the study of exotic nuclei with radioactive beams. Finally, the smooth correlations of many observables with N p N n leads to a study of the correlations between different collective observables themselves. The remarkable results stemming from this approach are summarized.