Nucleon Correlations Research Articles

Single-particle strength from nucleon transfer in oxygen isotopes: Sensitivity to model parameters

In the analysis of transfer reaction data to extract nuclear structure information the choice of input parameters to the reaction model such as distorting potentials and overlap functions has a significant impact. In this paper we consider a set of data for the ($d,t$) and ($d,^{3}\mathrm{He}$) reactions on $^{14,16,18}\mathrm{O}$ as a well-delimited subject for a study of the sensitivity of such analyses to different choices of distorting potentials and overlap functions with particular reference to a previous investigation of the variation of valence nucleon correlations as a function of the difference in nucleon separation energy $\mathrm{\ensuremath{\Delta}}S=|{S}_{p}\ensuremath{-}{S}_{n}|$ [Phys. Rev. Lett. 110, 122503 (2013)].

Background field Landau mode operators for the nucleon

The introduction of a uniform background magnetic field breaks threedimensional spatial symmetry for a charged particle and introduces Landau mode effects. Standard quark operators are inefficient at isolating the nucleon correlation function at nontrivial field strengths. We introduce novel quark operators constructed from the twodimensional Laplacian eigenmodes that describe a charged particle on a finite lattice. These eigenmode-projected quark operators provide enhanced precision for calculating nucleon energy shifts in a magnetic field. Preliminary results are obtained for the neutron and proton magnetic polarisabilities using these methods.

Dp breakup reaction investigation using polarized and unpolarized deuteron beam

Deuteron Spin Structure (DSS) collaboration program is aimed on few nucleon correlations investigation using unpolarized and polarized deuteron beam at intermediate energy range. Data of the dp breakup reaction have been obtained at energy range from 300 - 500 MeV of deuteron energy for various detector configurations in region where few nucleon correlations and relativistic effects can play significant role. Results are obtained in the form of S-curve and T20 and iT11 tensor analyzing powers in case of unpolarized and polarized data, respectively. Future plans on extracted deuteron beam of Nuclotron are concerned to tensor analyzing power T20 and spin correlation Cyy of 3He(d, p)4He reaction in the kinetic energy range between 1.0 and 1.75 GeV.

Study of nucleon correlations in nuclei by (p, p’) inelastic reaction at 1 GeV

The secondary proton polarization, differential cross section, and cross section ratios were measured in the (p, p’) inelastic reaction with nuclei at 1 GeV and a laboratory scattering angle of Θ = 210. The data were obtained over a wide range of the scattered proton momentum covering the pN quasielastic peak and high momentum region up to a momentum corresponding to excited level of the nucleus under investigation. Scattered protons were detected by the magnetic spectrometer equipped with a polarimeter based on multiwire proportional chambers and carbon analyzer. A structure in the polarization and cross section data, possibly related to the in-medium elastic scattering on nucleon correlations arising in nuclei, and a scaling of the scattering cross section ratios of the nuclei were observed in the high momentum range.

Nucleon correlations and the structure of [formula omitted

The structure of 71Zn was investigated by one-neutron transfer and heavy-ion induced complex (deep-inelastic) reactions using the GRETINA-CHICO2 and the Gammasphere setups, respectively. The observed inversion between the 9/2+ and 1/2− states is explained in terms of the role of neutron pairing correlations. Non-collective sequences of levels were delineated above the 9/2+ isomeric state. These are interpreted as being associated with a modest oblate deformation in the framework of Monte-Carlo shell-model calculations carried out with the A3DA-m Hamiltonian in the pfg9/2d5/2 valence space. Similarities with the structure of Ni402868 were observed and the shape-coexistence mechanism in the N=40 region of neutron-rich nuclei is discussed in terms of the so-called Type-II shell evolution, with an emphasis on proton–neutron correlations between valence nucleons, especially those involving the shape-driving g9/2 neutron orbital.

Nuclear medium effects in Drell–Yan process

We study the nuclear medium effects in Drell–Yan process using quark parton distribution functions calculated in a microscopic nuclear model which takes into account the effects of Fermi motion, nuclear binding and nucleon correlations through a relativistic nucleon spectral function. The contributions of π and ρ mesons as well as shadowing effects are also included. The beam energy loss is calculated using a phenomenological approach. The present theoretical results are compared with the experimental results of the E772 and E866 experiments. These results are applicable to the forthcoming experimental analysis of E906 Sea Quest experiment at the Fermi Lab.

Structure effects in polarization and cross sections for A(p, p’)X inelastic reactions on 40Ca and 12C nuclei at 1 GeV

The polarization of the secondary protons in inelastic (p,p') reaction on the 40Ca and 12C nuclei at the initial proton energy 1 GeV was measured in the wide range of the scattered proton momenta at a laboratory angle 21 degree. The cross section of the reactions were measured as well. The outgoing protons from the reaction were detected using a magnetic spectrometer equipped with a multiwire-proportional chambers polarimeter. A structure in the polarization and cross section data, related probably to scattering of the nucleon correlation in the nuclei, was observed.

Investigation of the dp Breakup and dp Elastic Reactions at Intermediate Energies at Nuclotron

The main goal of the deuteron spin structure project is to investigate the spin structure of nucleon–nucleon and three nucleon short-range correlations via the measurements of the polarization observables in the deuteron induced reactions at intermediate energies at Nuclotron (Dubna, Russia). In this framework, dp nonmesonic breakup and dp elastic reactions are investigated using internal target station. The dp breakup data are obtained with the detection of two outgoing protons at the angles of $$19^{\circ }$$ – $$54^{\circ }$$ in lab. frame at the deuteron energies of 300–500 MeV. The data of dp elastic scattering for the deuteron energies up to 2000 MeV are obtained in angular range $$70^{\circ }$$ – $$120^{\circ }$$ in cm. The further perspectives of the investigations using polarized deuteron beam as well as the studies of the $${}^3{\mathrm{He}}(d,p){}^4{\mathrm{He}}$$ reaction are discussed.

Nucleon--Nucleon Correlations and the Isospin and Spin Symmetry Energy

Nucleon--Nucleon Correlations and the Isospin and Spin Symmetry Energy

Probing the low and high density nuclear matter by hadron scattering

The subject of this report is connected with the widely discussed manifestation of in-medium effect in nuclear collisions. At present, the medium modification of hadron properties in the normal and in a dense nuclear matter is one of the fundamental questions of strong interaction physics. A new Glauber Monte Carlo model for hadron–nuclei interaction at intermediate energy is proposed. We utilized the principal assumptions as in the approaches of other authors describing nuclear collisions at high energy in the framework of the models without QGP. Yet, a number of new ingredients (noneikonal corrections, correlations of nucleons, in the nuclei, the nuclear Fermi motion, etc.) are introduced.

Investigation of the reaction 4Нe(γ, pn)d at energies below the meson-production threshold

Themomentum distributions of deuterons and nucleons from the reaction 4Не(γ, pn)d induced by bremsstrahlung photons whose spectrum extends up to the endpoint energy of 150 MeV weremeasured by means of a diffusion chamber placed in a magnetic field. These measurements were performed in four photon-energy intervals for deuterons and in the energy range between 100 and 150 MeV for nucleons. Angular and energy correlations of nucleons were measured at photon energies in the interval between 50 and 70 MeV. The results obtained in this way were analyzed on the basis of the quasideuteron model. The probability for final-state nucleon–deuteron interaction was estimated.

The interacting quasiparticle–phonon picture and odd–even nuclei. Overview and perspectives

The role of the nucleon correlations in the ground states of even–even nuclei on the properties of low-lying states in odd–even spherical and transitional nuclei is studied. We reason about this subject using the language of the quasiparticle–phonon model which we extend to take account of the existence of quasiparticle⊗phonon configurations in the wave functions of the ground states of the even–even cores. Of paramount importance to the structure of the low-lying states happens to be the quasiparticle–phonon interaction in the ground states which we evaluated using both the standard and the extended random phase approximations. Numerical calculations for nuclei in the barium and cadmium regions are performed using pairing and quadrupole–quadrupole interaction modes which have the dominant impact on the lowest-lying states’ structure. It is found that states with same angular momentum and parity become closer in energy as compared to the predictions of models disregarding the backward amplitudes, which turns out to be in accord with the experimental data. In addition we found that the interaction between the last quasiparticle and the ground-state phonon admixtures produces configurations which contribute significantly to the magnetic dipolemoment of odd-A nuclei. It also reveals a potential for reproducing their experimental values which proves impossible if this interaction is neglected.

Nuclear medium effects in [formula omitted] and [formula omitted] structure functions

Recent phenomenological analysis of experimental data on DIS processes induced by charged leptons and neutrinos/antineutrinos beams on nuclear targets by CTEQ collaboration has confirmed the observation of CCFR and NuTeV collaborations, that weak structure function F2AWeak(x,Q2) is different from electromagnetic structure function F2AEM(x,Q2) in a nucleus like iron, specially in the region of low x and Q2. In view of this observation we have made a study of nuclear medium effects on F2AWeak(x,Q2) and F2AEM(x,Q2) for a wide range of x and Q2 using a microscopic nuclear model. We have considered Fermi motion, binding energy, nucleon correlations, mesonic contributions from pion and rho mesons and shadowing effects to incorporate nuclear medium effects. The calculations are performed in a local density approximation using a relativistic nucleon spectral function which includes nucleon correlations. The numerical results in the case of iron nucleus are compared with the experimental data.

Identification of Nuclear Effects in Neutrino-Carbon Interactions at Low Three-Momentum Transfer.

Two different nuclear-medium effects are isolated using a low three-momentum transfer subsample of neutrino-carbon scattering data from the MINERvA neutrino experiment. The observed hadronic energy in charged-current ν_{μ} interactions is combined with muon kinematics to permit separation of the quasielastic and Δ(1232) resonance processes. First, we observe a small cross section at very low energy transfer that matches the expected screening effect of long-range nucleon correlations. Second, additions to the event rate in the kinematic region between the quasielastic and Δ resonance processes are needed to describe the data. The data in this kinematic region also have an enhanced population of multiproton final states. Contributions predicted for scattering from a nucleon pair have both properties; the model tested in this analysis is a significant improvement but does not fully describe the data. We present the results as a double-differential cross section to enable further investigation of nuclear models. Improved description of the effects of the nuclear environment are required by current and future neutrino oscillation experiments.

Pion–nucleon correlations in finite nuclei in a relativistic framework: Effects on the shell structure

The relativistic particle-vibration coupling (RPVC) model is extended by the inclusion of spin- and isospin-flip excitation modes into the phonon space, introducing a new mechanism of dynamical interaction between nucleons with different isospin in the nuclear medium. Protons and neutrons exchange by collective modes which are formed by isovector $\pi$ and $\rho$-mesons, in turn, softened considerably because of coupling to nucleons of the medium. These modes are investigated within the proton-neutron relativistic random phase approximation (pn-RRPA) and relativistic proton-neutron time blocking approximation (pn-RTBA). The appearance of isospin-flip states with sizable transition probabilities at low energies points out that they are likely to couple to the single-particle degrees of freedom and, in addition to isoscalar low-lying phonons, to modify their spectroscopic characteristics. Such a coupling is quantified for the shell structure of $^{100,132}$Sn and found significant for the location of the dominant single-particle states.

Study of polarization effects at Nuclotron

The major goal of the upgraded Nuclotron facility is to obtain the information on the equation-of-state for dense nuclear matter playing a key role in the under standing of the collapse supernovae and neutron stars stability. These studies can be performed either in heavy ion collisions or via the short-range few nucleon correlations. The obtained experimental results and future program with the use of polarized deuteron beam and the internal target station are discussed. The polarization studies for the NN, NA and dA reactions with the extracted deuteron beam at the BM@N setup are proposed. The further extension of the polarization program at BM@N is related with the study of the in-medium modification of the polarization for the strange and multi-strange baryons and the spin alignment for vector mesons decaying in hadronic modes.

Magnetic HexadecapoleγTransitions and Neutrino-Nuclear Responses in Medium-Heavy Nuclei

Neutrino-nuclear responses in the form of squares of nuclear matrix elements, NMEs, are crucial for studies of neutrino-induced processes in nuclei. In this work we investigate magnetic hexadecapole (M4) NMEs in medium-heavy nuclei. The experimentally derived NMEs,MEXP(M4), deduced from observed M4γtransition half-lives are compared with the single-quasiparticle (QP) NMEs,MQP(M4), and the microscopic quasiparticle-phonon model (MQPM) NMEsMMQPM(M4). The experimentally derived M4 NMEs are found to be reduced by a coefficientk≈0.29with respect toMQP(M4) and byk≈0.33with respect toMMQPM(M4). The M4 NMEs are reduced a little by the quasiparticle-phonon correlations of the MQPM wave functions but mainly by other nucleonic and nonnucleonic correlations which are not explicitly included in the MQPM. The found reduction rates are of the same order of magnitude as those for magnetic quadrupoleγtransitions and Gamow-Teller (GT) and spin-dipole (SD)βtransitions. The impacts of the found reduction coefficients on the magnitudes of the NMEs involved in astroneutrino interactions and neutrinoless double beta decays are discussed.

Nuclear medium effects in structure functions of nucleon at moderate [formula omitted

Recent experiments performed on inclusive electron scattering from nuclear targets have measured the nucleon electromagnetic structure functions F1(x,Q2), F2(x,Q2) and FL(x,Q2) in 12C, 27Al, 56Fe and 64Cu nuclei. The measurements have been done in the energy region of 1 GeV2<W2<4 GeV2 and Q2 region of 0.5 GeV2<Q2<4.5 GeV2. We have calculated nuclear medium effects in these structure functions arising due to the Fermi motion, binding energy, nucleon correlations, mesonic contributions from pion and rho mesons and shadowing effects. The calculations are performed in a local density approximation using a relativistic nucleon spectral function which includes nucleon correlations. The numerical results are compared with the recent experimental data from JLab and also with some earlier experiments.

Observation of a polarization structure in the 40Ca(p, p')X reaction at 1 GeV

The polarization of the secondary protons in the inelastic (p, p') reaction on the 40Ca nucleus at the initial proton energy 1 GeV was measured in a wide range of the scattered proton momenta at a laboratory angle Θ = 21°. The final protons from the reaction have been detected using the magnetic spectrometer equipped with multiwire-proportional chambers polarimeter. A structure of the polarization data, related probably to scattering off the nucleon correlations in the nucleus, has been observed.

Parity violating asymmetry with nuclear medium effects in deep inelastic [formula omitted] scattering

Recently parity violating asymmetry (APV) in the Deep Inelastic Scattering (DIS) of polarized electrons (e→) from deuterons has been measured at JLab and there exist future plans to measure this asymmetry from nuclear targets. In view of this we study nuclear medium effects in APV in the DIS of e→ from some nuclear targets like 12C, 56Fe and 208Pb. The effects of Fermi motion, binding energy and nucleon correlations are taken into account through the nucleon spectral function calculated in a local density approximation for nuclei. The pion and rho cloud contributions have also been taken into account. This model has been earlier used to study nuclear medium effects in the electromagnetic and weak interaction induced processes. The results are presented and discussed in view of the future JLab experiments.