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Diquark formation across a short-range nucleon-nucleon pair is proposed as the underlying QCD physics of short-range correlations (SRC) in nuclei. SRC pairs have been proposed as the cause of distorted quark behavior in nuclei; experimentally observed quark momentum distribution distortions termed the EMC effect. The strong spatial overlap of SRC pairs brings nucleon constituents within range of inter-nucleon QCD potentials and any bonds formed - such as the diquark bond - affects their distributions. In this SRC model, diquarks form in the 3C⊗3C→3¯C channel of SU(3)C acting on valence quarks from highly overlapping nucleon wavefunctions. The most energetically favorable diquark is a valence u quark from one nucleon with a valence d quark from the other in a spin-0 state bound together via continual single gluon exchange and an attractive quantum chromodynamics short-range potential. Formation of a new scalar isospin-singlet [ud] diquark across a NN pair is proposed as the primary QCD-level theoretical foundation for SRC models of distorted structure functions in A≥3 nuclei. Contributions from the higher mass spin-1 isospin triplet states (ud), (uu) and (dd) are possible, with the spin-1 (ud) diquark proposed as a higher mass but viable structure function distortion mechanism for the spin-1 ground state deuteron. Predictions are made for lepton scattering experiments on H3 and He3 nuclear targets, with implications for the coefficients of the 3-valence quark Fock states in the nucleon wavefunction.

We describe nuclear effects in structure functions of nuclei in DIS by means of a multiplicative factor β A (x) which differentiates the structure function of the bound nucleons from that of the free nucleons. Our analysis determines that β A (x) establishes a relation between the quark-gluon dynamics expressed by the bound nucleon structure functions and the nuclear dynamics as described by the well-known semi-empirical Bethe-Weizsäcker mass formula. This relation corroborates a connection between the underlying quark-gluon dynamics and the phenomenological nuclear dynamics. [ABSTRACT FROM AUTHOR]

The light-front formalism for a covariant description of the European Muon Collaboration (EMC) effect, already applied to He3, is formally extended to any nucleus, and used for actually calculating the 3H and He4 cases. The realistic and accurate nuclear description of few-nucleon bound systems, obtained with both phenomenological and chiral potentials, has been properly combined with the Poincaré covariance and macroscopic locality, automatically satisfying both number of particles and momentum sum rule. While retaining the on-mass-shell nucleon structure functions, one is then able to predict a sizable EMC effect for He4, as already observed for He3. Moreover, the impact on the EMC effect of both i) the short-range correlations, such as those generated by modern nuclear interactions, and ii) the ratio between the neutron and proton structure functions has been studied. The short-range correlations generated by retaining only the standard nuclear degrees of freedom act on the depth of the minimum in the EMC ratio, while the uncertainties linked to the ratio of neutron to proton structure functions are found to be very small. These light-front results facilitate ascribing deviations from experimental data due to genuine QCD effects, not included in a standard nuclear description, and initiating unbiased investigations.

Analytical expressions for the Transverse Momentum Dependent (TMD, or unintegrated) gluon and sea quark densities in nuclei are derived at leading order of QCD running coupling. The calculations are performed in the framework of the rescaling model and Kimber-Martin-Ryskin (KMR) prescription, where the Bessel-inspired behavior of parton densities at small Bjorken x values, obtained in the case of flat initial conditions in the double scaling QCD approximation, is applied. The derived expressions are used to evaluate the inclusive heavy flavor production in proton-lead collisions at the LHC. We find a good agreement of our results with latest experimental data collected by the CMS and ALICE Collaborations at s=5.02 GeV.

Hidden-color configurations are a key prediction of QCD with important physical consequences. In this work we examine a QCD color-singlet configuration in nuclei formed by combining six scalar [ud] diquarks in a strongly bound SU(3)C channel. The resulting hexadiquark state is a charge-2, spin-0, baryon number-4, isospin-0, color-singlet state. It contributes to alpha clustering in light nuclei and to the additional binding energy not saturated by ordinary nuclear forces in He4 as well as the alpha-nuclei sequence of interest for nuclear astrophysics. We show that the strongly bound combination of six scalar isospin-0 [ud] diquarks within the nuclear wave function - relative to free nucleons - provides a natural explanation of the EMC effect measured by the CLAS collaboration's comparison of nuclear parton distribution function ratios for a large range of nuclei. These experiments confirmed that the EMC effect; i.e., the distortion of quark distributions within nuclei, is dominantly identified with the dynamics of neutron-proton (“isophobic”) short-range correlations within the nuclear wave function rather than proton-proton or neutron-neutron correlations.

The fundamental theory of the strong interaction-quantum chromodynamics (QCD) - provides the foundational framework with which to describe and understand the key properties of atomic nuclei. A deep understanding of the explicit role of quarks and gluons in nuclei remains elusive however, as these effects have thus far been well-disguised by confinement effects in QCD which are encapsulated by a successful description in terms of effective hadronic degrees of freedom. The observation of the EMC effect has provided an enduring indication for explicit QCD effects in nuclei, and points to the medium modification of the bound protons and neutrons in the nuclear medium. Understanding the EMC effect is a major challenge for modern nuclear physics, and several key questions remain, such as understanding its flavor, spin, and momentum dependence. This manuscript provides a contemporary snapshot of our understanding of the role of QCD in nuclei and outlines possible pathways in experiment and theory that will help deepen our understanding of nuclei in the context of QCD.

A new and rigorous light-front formalism for electron deep inelastic scattering on unpolarized nuclei, in Bjorken limit, is proposed. It preserves Poincaré covariance, macroscopic locality, both number of particles and momentum sum rules. The approach is applied to the A=3 iso-doublet, very relevant for the flavor decomposition of the parton distribution functions and in view of the planned operation with unpolarized and polarized beams at the Electron-Ion Collider. At variance with previous light-front estimates, our procedure, including a realistic nuclear description and free-nucleon structure functions, predicts a sizable European Muon Collaboration effect for 3He. This will allow to analyze deviations from the proposed baseline in terms of genuine QCD effects. The extension to heavier nuclei is straightforward, although numerically challenging.

The behavior of the gluon density in nuclei is investigated in the framework of the rescaling model. [ABSTRACT FROM AUTHOR]

The light-front formalism for a covariant description of the European Muon Collaboration (EMC) effect, already applied to He 3 , is formally extended to any nucleus, and used for actually calculating the 3H and He 4 cases. The realistic and accurate nuclear description of few-nucleon bound systems, obtained with both phenomenological and chiral potentials, has been properly combined with the Poincaré covariance and macroscopic locality, automatically satisfying both number of particles and momentum sum rule. While retaining the on-mass-shell nucleon structure functions, one is then able to predict a sizable EMC effect for He 4 , as already observed for He 3. Moreover, the impact on the EMC effect of both i) the short-range correlations, such as those generated by modern nuclear interactions, and ii) the ratio between the neutron and proton structure functions has been studied. The short-range correlations generated by retaining only the standard nuclear degrees of freedom act on the depth of the minimum in the EMC ratio, while the uncertainties linked to the ratio of neutron to proton structure functions are found to be very small. These light-front results facilitate ascribing deviations from experimental data due to genuine QCD effects, not included in a standard nuclear description, and initiating unbiased investigations. [ABSTRACT FROM AUTHOR]

Analytical expressions for the Transverse Momentum Dependent (TMD, or unintegrated) gluon and sea quark densities in nuclei are derived at leading order of QCD running coupling. The calculations are performed in the framework of the rescaling model and Kimber-Martin-Ryskin (KMR) prescription, where the Bessel-inspired behavior of parton densities at small Bjorken x values, obtained in the case of flat initial conditions in the double scaling QCD approximation, is applied. The derived expressions are used to evaluate the inclusive heavy flavor production in proton-lead collisions at the LHC. We find a good agreement of our results with latest experimental data collected by the CMS and ALICE Collaborations at s = 5.02 GeV. [ABSTRACT FROM AUTHOR]

In the valon model a nucleon is assumed to be a bound state of three valence quark clusters (valons). On this base the nucleus structure function which are made from nucleons are analysed. Here in the frame work of perturbative quantum chromodynamics (pQCD) the structure of the valons are described at next to leading-order (NLO) approximation. Using the constituent-quark model, structure function of nucleon is largely investigated in the nuclear medium. For a series of nuclei with the nuclear mass A such that 2 ≤ A ≤ 40 within the kinetic region 0.0001 ≤ x ≤ 0.9 which covers a wide range of x Bjorken variable, the theoretical predications are in good agreement with the existing lepton-nucleus data. A better and fair description of experimental data can be done, considering the shadowing effect for small values of x i.e. x < 0.01. Using the valon model, we do an analysis at the NLO approximation while shadowing effect is employed. A comparison between our theoretical prediction for nuclear parton distribution functions (nPDFs) and the results from recent collaborations like AT12 and HKN07 sets have been done. The results of our calculations are in good agreement with the experimental data in deep inelastic scattering (DIS) processes which covers an extended region of x-variable, including the small and also large x amounts and also with some theoretical models. [ABSTRACT FROM AUTHOR]

In the 35 years since the European Muon Collaboration announced the astonishing result that the valence structure of a nucleus was very different from that of a free nucleon, many explanations have been suggested. The first of the two most promising explanations is based upon the different effects of the strong Lorentz scalar and vector mean fields known to exist in a nucleus on the internal structure of the nucleon-like clusters which occupy shell model states. The second links the effect to the modification of the structure of nucleons involved in short-range correlations, which are far off their mass shell. We explore some of the methods which have been proposed to give complementary information on this puzzle, especially the spin-dependent EMC effect and the isovector EMC effect, both proposed by Cloët, Bentz and Thomas. It is shown that the predictions for the spin-dependent EMC effect, in particular, differ substantially within the mean-field and short-range correlation approaches. Hence, the measurement of the spin-dependent EMC effect at Jefferson Lab should give us a deeper understanding of the origin of the EMC effect and, indeed, of the structure of atomic nuclei. [ABSTRACT FROM AUTHOR]

The ratios of the in-medium to free nucleon structure functions for the unpolarized and polarized cases are obtained using the MIT bag model for the free case, along with the QMC model to incorporate the in-medium modifications of the structure functions. As discussed in earlier work, the observed nuclear EMC effect is reasonably well described. This gives us confidence to investigate the predictions of the model for the polarized EMC effect, the ratio g 1 ⁎ ( x ) / g 1 ( x ) for a bound proton to that of a free proton. This ratio is found to be substantially different from unity and very similar in shape and size to that found in the unpolarized case. This prediction of such a fundamental change in the valence structure of a bound nucleon needs to be tested experimentally at the earliest opportunity. [ABSTRACT FROM AUTHOR]

While the constituent quark model (CQM), in which the quarks are assumed to be the complex objects, is used to calculate the parton distribution functions of the iso-scalar lithium-6 ( 6 Li) nucleus, the u – d constituent quark distribution functions of the 6 Li nucleus are evaluated from the valence quark exchange formalism (VQEF) for the A = 6 iso-scalar system. After computing the valence quark, sea quark, and gluon distribution functions in the constituent quark exchange model (CQEM, i.e., CQM + VQEF ), the nucleus structure function is calculated for the 6 Li nucleus at the leading order ( LO ) and the next-to-leading-order ( NLO ) levels to extract the European muon collaboration (EMC) ratio, at different hard scales, using the standard Dokshitzer–Gribov–Lipatov–Altarelli–Parisi (DGALP) evolution equations. The outcomes are compared with those of our previous works and the available NMC experimental data, and various physical points are discussed. It is observed that the present EMC ratios are considerably improved compared with those of our previous works, in which only the valence quark distributions were considered to calculate the EMC ratio, and are closer to the NMC data. Finally, it is concluded that at a given appropriate hard scale, the LO approximation may be enough for calculating the nucleus EMC ratio. [ABSTRACT FROM AUTHOR]

A new and rigorous light-front formalism for electron deep inelastic scattering on unpolarized nuclei, in Bjorken limit, is proposed. It preserves Poincaré covariance, macroscopic locality, both number of particles and momentum sum rules. The approach is applied to the A=3 iso-doublet, very relevant for the flavor decomposition of the parton distribution functions and in view of the planned operation with unpolarized and polarized beams at the Electron-Ion Collider. At variance with previous light-front estimates, our procedure, including a realistic nuclear description and free-nucleon structure functions, predicts a sizable European Muon Collaboration effect for 3He. This will allow to analyze deviations from the proposed baseline in terms of genuine QCD effects. The extension to heavier nuclei is straightforward, although numerically challenging. [ABSTRACT FROM AUTHOR]

In this paper, we calculate nuclear structure function and EMC effect of 40Ca and 56Fe nuclei. To achive the goals, we consider Fermi motion and binding energy contrbiution in the harmonic oscillator model. In this model, harmonic oscillator parameter ħω related to shells root mean square radius and for free nucleon structure functions, is obtained from GRV’s free nucleon structure functions. Then, we calculate differential cross section of lepton scattering from those nuclei at the E=4.8 GeV and E=4.032 GeV. The obtained results show good agreement with available experimental data.

Diquark formation across a short-range nucleon-nucleon pair is proposed as the underlying QCD physics of short-range correlations (SRC) in nuclei. SRC pairs have been proposed as the cause of distorted quark behavior in nuclei; experimentally observed quark momentum distribution distortions termed the EMC effect. The strong spatial overlap of SRC pairs brings nucleon constituents within range of inter-nucleon QCD potentials and any bonds formed - such as the diquark bond - affects their distributions. In this SRC model, diquarks form in the 3 C ⊗ 3 C → 3 ¯ C channel of SU (3) C acting on valence quarks from highly overlapping nucleon wavefunctions. The most energetically favorable diquark is a valence u quark from one nucleon with a valence d quark from the other in a spin-0 state bound together via continual single gluon exchange and an attractive quantum chromodynamics short-range potential. Formation of a new scalar isospin-singlet [ u d ] diquark across a NN pair is proposed as the primary QCD-level theoretical foundation for SRC models of distorted structure functions in A ≥ 3 nuclei. Contributions from the higher mass spin-1 isospin triplet states (u d) , (u u) and (d d) are possible, with the spin-1 (u d) diquark proposed as a higher mass but viable structure function distortion mechanism for the spin-1 ground state deuteron. Predictions are made for lepton scattering experiments on H 3 and He 3 nuclear targets, with implications for the coefficients of the 3-valence quark Fock states in the nucleon wavefunction. [ABSTRACT FROM AUTHOR]

By using the convolution formalism which consists of Fermi motion and binding effect, we investigate the deep inelastic electron scattering from A=3 mirror in the deep-valence region. The initial valence quark input is taken from the GRVs (Gluck, Reya and Vogt) fitting procedure and the next-to-leading order QCD evolution on FP2 (x,Q2) which gives very good fit to the available data in the (x,Q2)-plane. It is shown that the free neutron to proton structure function ratios can be extracted from the corresponding EMC ratios for 3He and 3H mirror nuclei using the self - consistent iteration procedure and the results are in good agreement with other theoretical models as well as the current available experimental data and especially the projected data expected from the proposed 11GeV Jefferson Laboratory in near future.