Nucleons In Nucleus Research Articles

Isovector Pair Correlations of Nucleons in Nuclei

A finite boson representation of fermion operators is obtained. The collective Hamiltonian for a description of the pair excitation is constructed and the collective potential energy is analyzed. The collective modes related to the addition and removal of pair of particles are partitioned off the variety of nuclear degrees of freedom.

GEOMETRICAL STRUCTURE OF LEAD NUCLEI AND OF SOME OTHER CHEMICAL ELEMENTS

The interior structure of nucleus of the chemical element lead is given in the form of shell sequence of polyhedrons. This sequence represented with the help of some arithmetic progression of positive numbers, which connects with hypothesis of α-particles synthesis of nuclei. Other chemical elements also are considering with this point of view. On the graph of abundance of chemical elements in Solar system picks correspond to these elements. In the work the Table of numbers of nucleons in nuclei of these elements is proposed and we obtain combinatoric type of polyhedrons, which considering as shells of these chemical elements.

SIDES: Nucleon–nucleus elastic scattering code for nonlocal potential

We introduce the package SIDES (Schrödinger Integro-Differential Equation Solver) that solves the integro-differential Schrödinger equation for elastic scattering of a nonlocal optical potential in coordinate space. The code is capable of treating the Coulomb interaction without restrictions. The method is based on previous developments by Jacques Raynal in the DWBA07 code. Elastic scattering observables such as differential and integral cross sections, as well as analyzing power and spin rotation functions for both neutron and proton projectiles are evaluated, with no restriction on the type of nonlocality of the potential nor on the beam energy. The corresponding distorted wavefunctions are calculated as well. The SIDES package includes a Perey–Buck potential generator with two parametrizations. It includes as well local potential parametrizations and allows for mixing local and nonlocal contributions. Benchmarks are performed and discussed. Program summaryProgram Title: SIDESProgram Files doi:http://dx.doi.org/10.17632/cmpjgyrngr.1Licensing provisions: GNU General Public License, Version 2Programming language: FORTRAN-90Nature of problem: The description of nucleon elastic scattering off a target nucleus involves solving the Schrödinger’s wave equation for positive incident energy. The determination of scattering observables calls for accurate treatments of the continuum. The effective coupling between the projectile and the target is accounted for by an optical potential, an operator which is by nature complex, energy-dependent and nonlocal. The coupling becomes long-range in the case of charged projectiles. In a general scenario under nonlocal potentials, Schrödinger’s equation becomes an integro-differential equation.Solution method: SIDES solves the Schrödinger integro-differential equation numerically by matrix inversion using Gibbs, Numerov or a modified Numerov method with a uniform radial mesh in a box. The solution is refined by an iterative procedure until a specified precision is achieved. To obtain elastic scattering observables, the associated phase-shifts are calculated via matching of the numerical solution with its analytic asymptotic behavior.

Diffractive deeply virtual Compton scattering

Diffractive deeply virtual Compton scattering (DiDVCS) is the process $\gamma^*(- Q^2) + N \rightarrow \rho^0 + \gamma^* (Q'^2)+ N'$, where N is a nucleon or light nucleus, in the kinematical regime of large rapidity gap between the $\rho^0$ and the final photon-nucleus system, and in the generalized Bjorken regime where both photon virtualities $Q^2$ and $ Q'^2$ are large. We show that this process has the unique virtue of combining the large diffractive cross sections at high energy with the tomographic ability of deeply virtual Compton scattering to scrutinize the quark and gluon content of nucleons and light nuclei. Its study at an electron-ion collider would enlighten the internal structure of hadrons.

Microscopic optical potentials including breakup effects for elastic scattering

Abstract We construct a microscopic optical potential including breakup effects for the elastic scattering of weakly binding projectiles within the Glauber model, in which a nucleon–nucleus potential is derived using the $g$-matrix folding model. The derived microscopic optical potential is referred to as the eikonal potential. For $d$ scattering, calculation with the eikonal potential, i.e., the EP model, reasonably reproduces the result of the exact calculation with the continuum-discretized coupled-channels method at intermediate energies. From the properties of the EP model, the inaccuracy of the eikonal approximation used in the Glauber model is partially excluded. Also analyzed with the eikonal potential is the scattering of $^6$He from $^{12}$C, and its applicability to scattering with many-body projectiles is shown.

Exploring the Structure of the Bound Proton with Deeply Virtual Compton Scattering

In the past two decades, deeply virtual Compton scattering of electrons has been successfully used to advance our knowledge of the partonic structure of the free proton and investigate correlations between the transverse position and the longitudinal momentum of quarks inside the nucleon. Meanwhile, the structure of bound nucleons in nuclei has been studied in inclusive deep-inelastic lepton scattering experiments off nuclear targets, showing a significant difference in longitudinal momentum distribution of quarks inside the bound nucleon, known as the EMC effect. In this Letter, we report the first beam spin asymmetry (BSA) measurement of exclusive deeply virtual Compton scattering off a proton bound in ^{4}He. The data used here were accumulated using a 6GeV longitudinally polarized electron beam incident on a pressurized ^{4}He gaseous target placed within the CLAS spectrometer in Hall-B at the Thomas Jefferson National Accelerator Facility. The azimuthal angle (ϕ) dependence of the BSA was studied in a wide range of virtual photon and scattered proton kinematics. The Q^{2}, x_{B}, and t dependencies of the BSA on the bound proton are compared with those on the free proton. In the whole kinematical region of our measurements, the BSA on the bound proton is smaller by 20% to 40%, indicating possible medium modification of its partonic structure.

Quasi-elastic polarization-transfer measurements on the deuteron in anti-parallel kinematics

We present measurements of the polarization-transfer components in the H2(e→,e′p→) reaction, covering a previously unexplored kinematic region with large positive (anti-parallel) missing momentum, pmiss, up to 220MeV/c, and Q2=0.65(GeV/c)2. These measurements, performed at the Mainz Microtron (MAMI), were motivated by theoretical calculations which predict small final-state interaction (FSI) effects in these kinematics, making them favorable for searching for medium modifications of bound nucleons in nuclei. We find in this kinematic region that the measured polarization-transfer components Px and Pz and their ratio agree with the theoretical calculations, which use free-proton form factors. Using this, we establish upper limits on possible medium effects that modify the bound proton's form factor ratio GE/GM at the level of a few percent. We also compare the measured polarization-transfer components and their ratio for 2H to those of a free (moving) proton. We find that the universal behavior of 2H, 4He and 12C in the double ratio (Px/Pz)A(Px/Pz)H1 is maintained in the positive missing-momentum region.

Central and peripheral hadron–nucleus collisions in the Additive Quark Model

Peripheral nucleon–nucleus collisions occur at high energies mainly through the interaction with one constituent quark from the incident nucleon. The central collisions should involve all three constituent quarks and each of them can interact several times. We calculate the average number of quark–nucleus interactions for both the cases in good agreement with the experimental data on [Formula: see text]-meson, [Formula: see text] and all charged secondaries productions in [Formula: see text] collisions at LHC energy [Formula: see text] TeV.

A nucleon–nucleus optical model for A ≤ 13 nuclei at 65–75 MeV projectile energy

Small nuclei (A < 16) test the limits of optical potential theory, most recently there has been difficulty matching the helium isotopes’ analyzing powers at 71 MeV per nucleon. We provide a phenomenological optical potential that has been fit to a variety of experimental proton–nucleus and neutron–nucleus scattering data between A = 4 and A = 13 with a projectile energy between 65 and 75 MeV; the motivation being the helium isotopes. The resulting potential is dependent only on projectile isospin, neutron, and proton numbers. It fits the analyzing power of 6He satisfactorily only by including a non-traditional negative surface depth and a spin–orbit force which is significant at a distance larger than traditional models. We offer physical interpretations of our non-traditional results, suggest directions for microscopic calculations, and proffer calculations for future experiments.

Probing high-momentum protons and neutrons in neutron-rich nuclei

The atomic nucleus is one of the densest and most complex quantum-mechanical systems in nature. Nuclei account for nearly all the mass of the visible Universe. The properties of individual nucleons (protons and neutrons) in nuclei can be probed by scattering a high-energy particle from the nucleus and detecting this particle after it scatters, often also detecting an additional knocked-out proton. Analysis of electron- and proton-scattering experiments suggests that some nucleons in nuclei form close-proximity neutron-proton pairs1-12 with high nucleon momentum, greater than the nuclear Fermi momentum. However, how excess neutrons in neutron-rich nuclei form such close-proximity pairs remains unclear. Here we measure protons and, for the first time, neutrons knocked out of medium-to-heavy nuclei by high-energy electrons and show that the fraction of high-momentum protons increases markedly with the neutron excess in the nucleus, whereas the fraction of high-momentum neutrons decreases slightly. This effect is surprising because in the classical nuclear shell model, protons and neutrons obey Fermi statistics, have little correlation and mostly fill independent energy shells. These high-momentum nucleons in neutron-rich nuclei are important for understanding nuclear parton distribution functions(the partial momentum distribution of the constituents of the nucleon) and changes in the quark distributions of nucleons bound in nuclei (the EMC effect)1,13,14. They are also relevant for the interpretation of neutrino-oscillation measurements15 and understanding of neutron-rich systems such as neutron stars3,16.

Strong absorption model with antisymmetric S-matrix

We present a strong absorption model with an [Formula: see text]-matrix in a new form of an antisymmetrized Fermi distribution for describing diffraction patterns of neutron–nucleus scattering at intermediate energies. The proposed antisymmetric [Formula: see text]-matrix has a form close to the conventional one and allows to obtain exact analytical expressions for the damping factor that determines the elastic scattering amplitude and the total cross-sections for interaction, reactions and elastic scattering. The use of an antisymmetrized Fermi function instead of the usual Fermi function in successful strong absorption models basically does not notably affect the calculated nucleon–nucleus elastic scattering differential cross-sections in the intermediate energy region.

Neutrino Energy Reconstruction Methods Using Electron Scattering Data

The precise measurement of neutrino properties is among the highest priorities in fundamental particle physics, involving many experiments worldwide. Since the experiments rely on the interactions of neutrinos with bound nucleons inside atomic nuclei, the planned advances in the scope and precision of these experiments requires a commensurate effort in the understanding and modeling of the hadronic and nuclear physics of these interactions, which is incorporated as a nuclear model in neutrino event generators. This model is essential to every phase of experimental analyses and its theoretical uncertainties play an important role in interpreting every result.Any nuclear model used to describe neutrino-nucleus scattering should first be validated against these data. Since the vector part of the weak response is related to the electro-magnetic response through CVC, such a test is necessary, but not sufficient, to ensure the validity of a model for given kinematics, namely given values of the transferred energy ω(= ν for neutrinos) and momentum q. The main challenges in connecting electron and neutrino reactions:• matching models used to predict neutrino-nucleus observables to electron scattering data.• expanding theory to include more semi-inclusive predictions.• provide semi-inclusive neutron, proton and pion data sets with broad angular range.The cross section for neutrino scattering from nuclei is sensitive to the same underlying structure determined by QCD, and as probed with pure electromagnetic processes, such as charged lepton scattering from nucleons and nuclei. As such, there are a number of ways that electron scattering data inform ν - A cross section modeling, as well as providing a test-bed for model validation. In contrast to past and current neutrino beams, charged lepton scattering has the distinct advantage of nearly monochromatic beams with well determined energies, allowing for a significantly cleaner kinematic separation of the various production mechanisms in inclusive scattering, such as reso- nance production and nucleon elastic scattering. In addition to providing important experimental input such as nucleon isovector elastic form factors and resonance transition form factors, electron scattering data provide critical information on the distributions of initial state momentum and energy for nucleons in nuclei, the importance of 2-body currents and final state interaction effects. In this analysis, we will give a brief overview of the experimental input provided by electron scattering data.

On the Production of J/ψ-Mesons in Pion–Nucleus Collisions

The processes of J/ψ-mesons production in pion–nucleus collisions are considered. For the determination of the inclusive spectra πA → J/ψX, the model was used which takes into account the energy losses of hard gluons in the interactions of hadron states with the nucleus nucleons. The results of calculations are presented together with the experimental data of NA3 Collaboration on π–Pt195 → J/ψX spectra at the incident pions energies of 150 and 280 GeV.

Search for three-nucleon short-range correlations in light nuclei

We present new data probing short-range correlations (SRCs) in nuclei through the measurement of electron scattering off high-momentum nucleons in nuclei. The inclusive 4He/3He cross section ratio is observed to be both x and Q2 independent for 1.5 < x < 2, confirming the dominance of two- nucleon (2N) short-range correlations (SRCs). For x > 2, our data do not support a previous claim of three-nucleon (3N) correlation dominance. While contributions beyond those from stationary 2N- SRCs are observed, our data show that isolating 3N-SRCs is more complicated than for 2N-SRCs.

Microscopic optical potential obtained from energy-density-functional approach for neutron–nucleus elastic scattering

Nucleon–nucleus (NA) optical potentials are microscopically generated from a fully self-consistent framework of the particle-vibration coupling (PVC), in which the nucleon–nucleon (NN) effective interaction of the Skyrme type is consistently used to describe the Hartree–Fock (HF) mean-field, the small amplitude collective motions of the target, and the particle-collective states coupling. For the first time, a systematic calculation of low-energy NA elastic scattering off a series of doubly closed-shell nuclei is carried out without ad hoc adjusted parameters. Angular distributions obtained using the present optical potentials are in good agreement with the experimental data. This will be a major step forward in the applications of the Skyrme energy-density-functional theory to build up the global microscopic optical potentials, which are expected to be a powerful tool for the study of unstable (exotic) nuclei at low-incident nucleon energies.

Width of fission-fragment mass yield at simple statistical approach

Simple expression for the temperature dependence of the width of fission-fragment mass yields is obtained for high excitation energies. The width depends on the number of nucleons in nuclei, the volume and surface terms of the energy level density parameter, the temperature and the stiffness parameter of the potential related to mass-asymmetric degree of freedom. The contribution of the surface term of the energy level density parameter into the width is important at temperatures [Formula: see text][Formula: see text]MeV.

First lattice QCD study of the gluonic structure of light nuclei

The role of gluons in the structure of the nucleon and light nuclei is investigated using lattice quantum chromodynamics (QCD) calculations. The first moment of the unpolarised gluon distribution is studied in nuclei up to atomic number $A=3$ at quark masses corresponding to pion masses of $m_\pi\sim 450$ and $806$ MeV. Nuclear modification of this quantity defines a gluonic analogue of the EMC effect and is constrained to be less than $\sim 10$% in these nuclei. This is consistent with expectations from phenomenological quark distributions and the momentum sum rule. In the deuteron, the combination of gluon distributions corresponding to the $b_1$ structure function is found to have a small first moment compared with the corresponding momentum fraction. The first moment of the gluon transversity structure function is also investigated in the spin-1 deuteron, where a non-zero signal is observed at $m_\pi \sim 806$ MeV. This is the first indication of gluon contributions to nuclear structure that can not be associated with an individual nucleon.

Searching for high energy cosmic-ray protons using a new way of finding and tracking particles in stratospheric X-ray emulsion chambers (According to data from the Russian–Japanese RUNJOB experiment)

An continuing search for primary particles is performed using a new means of finding and tracking particles in nuclear emulsions. Particle interactions registered in stratospheric X-ray emulsion chambers (XECs) are attributed to nucleon–nuclei interactions recorded in the Russian–Japanese RUNJOB experiment. According to the data from processing the interactions between galactic particles and matter in XECs RUNJOB-3B, 6A, and RUNJOB-11A, 11B with energy thresholds ΣE γ ≥ 3 and ΣE γ ≥ 5 TeV, respectively, around 50% of all proton tracks went unidentified, which coincides with the initial results from the RUNJOB experiment.

Active target MAIKo to investigate cluster structures in unstable nuclei

Study on clustering of nucleons in nuclei is recently focusing on unstable nuclei where new kinds of structures, namely molecular structures with excess nucleons, are predicted. The Coulomb shift of energy in the mirror system is suggested to reflect the size of these structures. Although the missing mass spectroscopy is expected to give access to these structures even beyond particle decay thresholds without any biases in excitation energy spectra but the detection of very low energy particles is challenging. To satisfy the requirement, a new active target system MAIKo has been developed at RCNP. The detector was commissioned using a 13C beam under the same kinematical condition as that of RI beam experiments.

Relativistic effects and three-nucleon forces in nuclear matter and nuclei

We review a large body of predictions obtained within the framework of relativistic meson theory together with the Dirac–Brueckner–Hartree–Fock approach to nuclear matter and finite nuclei. The success of this method has been largely related to its ability to take into account important three-body effects. Therefore, the overarching theme of this paper is the interpretation of the so-called “Dirac effects” as an effective three-nucleon force. We address the equation of state (EoS) of isospin symmetric and asymmetric nucleonic matter and related issues, ranging from proton and neutron density distributions to momentum distributions and short-range correlations. A central part of the discussion is devoted to the optical model potential for nucleon–nucleus scattering. We also take the opportunity to explore similarities and differences with predictions based on the increasingly popular chiral effective field theory.