Nucleon Contribution Research Articles

Systematic investigation of trace anomaly contribution in nucleon mass

In this work, under the framework of the vector meson dominance model, the trace anomaly contribution value inside neutrons is extracted for the first time based on vector meson photoproduction data. Furthermore, we systematically compare and analyze the trace anomaly contributions of protons and neutrons. The results show that the trace anomaly contributions of protons and neutrons are close, which indirectly confirms that their internal structures and dynamic properties may have certain similarities. In addition, the main factors affecting the extraction of the trace anomaly contribution of nucleons are discussed in detail. This study not only provides a theoretical basis for us to better understand the source of nucleon mass but also makes a useful exploration and discussion on how to extract the trace anomaly contribution of nucleons more accurately in the future. Published by the American Physical Society 2024

Chiral crossover versus chiral density wave in dense nuclear matter

We employ a model based on nucleonic and mesonic degrees of freedom to discuss the competition between isotropic and anisotropic phases in cold and dense matter. Assuming isotropy, the model exhibits a chiral phase transition which is of second order in the chiral limit and becomes a crossover in the case of a realistic pion mass. This observation crucially depends on the presence of the nucleonic vacuum contribution. Allowing for an anisotropic phase in the form of a chiral density wave can disrupt the smooth crossover. We identify the regions in the parameter space of the model where a chiral density wave is energetically preferred. A high-density reappearance of the chiral density wave with unphysical behavior, as seen in previous studies, is avoided by a suitable renormalization scheme. A nonzero pion mass tends to disfavor the anisotropic phase compared to the chiral limit and we find that, within our model, the chiral density wave is only realized for baryon densities of at least about 6 times nuclear saturation density. Published by the American Physical Society 2024

Parity-doublet bands in the odd- A isotones U237 and Pu239 investigated by a particle-number-conserving method based on the cranked shell model

Based on the reflection-asymmetric Nilsson potential, the parity-doublet rotational bands in odd-$A$ isotones \element{237}U and \element{239}Pu have been investigated by using the particle-number-conserving (PNC) method in the framework of the cranked shell model (CSM). The experimental kinematic moments of inertia (MOIs) and angular momentum alignments are reproduced very well by the PNC-CSM calculations. The significant differences of rotational properties between \element{237}U and \element{239}Pu are explained with the contribution of nucleons occupying proton octupole-correlation pairs of $\pi ^{2} i_{13/2}f_{7/2}$. The upbendings of moments of inertia of the parity-doublet bands in \element{237}U are due to the interference terms of alignments of protons occupying $\pi f_{7/2}$ (${1/2}$) and the high-$j$ intruder $\pi i_{13/2}$ $(1/2, 3/2)$ orbitals. The splittings between the simplex partner bands of the parity-doublet bands in both \element{237}U and \element{239}Pu result from the contribution of alignment of neutron occupying the $\nu d_{5/2}$ ($1/2$) orbital.

Multimessenger Implications of Sub-PeV Diffuse Galactic Gamma-Ray Emission

Abstract The diffuse Galactic gamma-ray flux between 0.1 and 1 PeV has recently been measured by the Tibet ASγ Collaboration. The flux and spectrum are consistent with the decay of neutral pions from hadronuclear interactions between Galactic cosmic rays and the interstellar medium (ISM). We derive the flux of the Galactic diffuse neutrino emission from the same interaction process that produces the gamma rays. Our calculation accounts for the effect of gamma-ray attenuation inside the Milky Way and uncertainties due to the spectrum and distribution of cosmic rays, gas density, and infrared emission of the ISM. We find that the contribution from the Galactic plane (GP) to the all-sky neutrino flux is ≲5%–10% around 100 TeV. The Galactic and extragalactic neutrino intensities are comparable in the GP region. Our results are consistent with the upper limit reported by the IceCube and ANTARES Collaborations, and predict that next-generation neutrino experiments may observe the Galactic component. We also show that the Tibet ASγ data imply either an additional component in the cosmic-ray nucleon spectrum or contribution from discrete sources, including PeVatrons such as superbubbles and hypernova remnants, and PeV electron accelerators. Future multimessenger observations between 1 TeV and 1 PeV are crucial to decomposing the origin of sub-PeV gamma-rays.

Measurement of the tensor analyzing power T20 for the reaction γd → pnπ0

This paper presents new results for the [Formula: see text]-component of the tensor analyzing power of the reaction [Formula: see text] in the photon energy range of [Formula: see text]. The experimental statistics accumulated in 2013 at the VEPP-3 accelerator-storage complex is used. The reaction events are identified by the coincidence registration of the proton and two [Formula: see text]-quanta from the decay of the neutral pion. To determine the [Formula: see text]-component, the asymmetry of the yields with respect to the change of sign of the tensor polarization of the deuterium target is measured. The experimental results are compared with the theoretical calculations in which the MAID 2007 model is used as the elementary pion–nucleon photoproduction amplitude and contributions from the pion–nucleon and nucleon–nucleon rescattering are taken into account.

Equation of State Effects in Core-Collapse Supernovae.

We investigate the impact of different properties of the nuclear equation of state in core-collapse supernovae, with a focus on the proto-neutron-star contraction and its impact on the shock evolution. To this end, we introduce a range of equations of state that vary the nucleon effective mass, incompressibility, symmetry energy, and nuclear saturation point. This allows us to point to the different effects in changing these properties from the Lattimer and Swesty to the Shen etal. equations of state, the two most commonly used equations of state in simulations. In particular, we trace the contraction behavior to the effective mass, which determines the thermal nucleonic contributions to the equation of state. Larger effective masses lead to lower pressures at nuclear densities and a lower thermal index. This results in a more rapid contraction of the proto-neutron star and consequently higher neutrino energies, which aids the shock evolution to a faster explosion.

Sub-threshold J/ψ and ϒ production in γA collisions

We study sub-threshold heavy quarkonium (J/ψ and ϒ) photo-productions in γA collisions as an independent test of the universality of the nucleon-nucleon short range correlation (SRC) in nuclear scattering processes. Just below the γp threshold, the cross section is dominated by the mean field contribution of nucleons inside the nucleus. The SRC contributions start to dominate at lower photon energies, depending on the fraction of the SRC pairs in the target nucleus. We give an estimate of the cross sections in the sub-threshold region both for J/ψ and ϒ. This may be helpful for future measurements at JLab as well as at the Electron-Ion Collider in the U.S., and especially in China.

Role of magic numbers in thermodynamic quantities of 206Pb and 138Ba using BCS and Lipkin-Nogami models

The level density is calculated using the Barden-Cooper-Schriefer (BCS) and Lipkin-Nogami (LN) models for 206Pb and 138Ba nuclei and compared with the experimental data. It has been shown that the calculated level densities using both models are highly matched with the experimental data. The spin cut off factor, moment of inertia, excitation energy, and entropy were calculated using the above mentioned models. The protons in the 206Pb nucleus occupy a closed shell and the 138Ba nucleus has a closed neutron shell. It was revealed that the contribution of the nucleons with magic number to the mentioned thermodynamic quantities is less than that of the nucleons from open shells at low temperature.

Equilibrium of nuclear matter in QCD sum rules

We calculate the nucleon parameters in symmetric nuclear matter employing the QCD sum rules approach. We focus on the average energy per nucleon and study the equilibrium states of the matter. We treat the matter as a relativistic system of interacting nucleons. Assuming the dependence of the nucleon mass on the light quark mass $m_q$ to be more important than that of nucleon interactions we find that the contribution of the relativistic nucleons to the scalar quark condensate can be expressed as that caused by free nucleons at rest multiplied by the density dependent factor $F(\rho)$. We demonstrate that there are no equilibrium states while we include only the condensates with dimension $d \leq 3$. There are equilibrium states if we include the lowest order radiative corrections and the condensates with $d \leq 4$. They manifest themselves for the nucleon sigma term $\sigma_N >60$ MeV. Including the condensates with $ d \leq 6$ we find equilibrium states of nuclear matter for $\sigma_N> 41$ MeV. In all cases the equilibrium states are due to influence of the relativistic motion of the nucleons composing the matter on the scalar quark condensate.

Transport coefficients in neutron star cores in BHF approach. Comparison of different nucleon potentials

Thermal conductivity and shear viscosity of npeµ matter in non-superfluid neutron star cores are considered in the framework of Brueckner-Hartree-Fock many-body theory. We extend our previous work (Shternin et al 2013 PRC 88 065803) by analysing different nucleon-nucleon potentials and different three-body forces. We find that the use of different potentials leads up to one order of magnitude variations in the values of the nucleon contribution to transport coefficients. The nucleon contribution dominates the thermal conductivity, but for all considered models the shear viscosity is dominated by leptons.

Efektyvnyj yaderno-yadernyj potencial z uraxuvannyam vnesku kinetychnoyi enerhiyi nukloniv ta pererizy pruzhnoho rozsiyannya i pidbar’yernoho zlyttya

The microscopic double-folding approach to the calculation of the nucleus-nucleus interaction has been discussed in detail. The nucleus-nucleus interaction potentials for the 16O+208Pb system with and without the contribution of the kinetic energy of nucleons in the nuclei are constructed, and the cross-sections of elastic scattering and subbarrier fusion are calculated. The experimental values of those cross-sections are shown to be described well, if the contribution of nucleons’ kinetic energy is taken into account.

About the validity of complex mass scheme for the Δ resonance and higher energy region approaches

It is a well known fact that when a resonance (R) is produced and decays, its unperturbed propagator will be singular at when it appears in an s-type Feynman pole graph. Nevertheless this is not a problem, since it must be dressed by the successive re-interactions of the resonance with itself to all orders through the non-pole T-matrix, which we include in this work for the self-energy one-loop pion–nucleon contributions. Recently, we have shown that within the one-loop approximation for the absorptive part it is possible to justify the use of the complex-mass description over the unperturbed propagator, adopted in previous calculations to treat pion–nucleon elastic and radiative scattering, and photo and weak pion production in the resonance region. Here we discuss the limits of the validity of this approximation, since in actual calculations we must go over this range. We show that, when the resonance energy is increased above , this approach becomes invalid and an alternative approximation should be considered. In addition, we discuss the usual energy dependent width approximation, present in several actual isobar models used to analyze the last neutrino scattering experiments, and show that also it could be unappropriate.

Viscosity of neutron star matter andr-modes in rotating pulsars

We study viscosity of the neutron star matter and $r$-mode instability in rotating neutron stars. Contributions to the shear and bulk viscosities from various processes are calculated with account of in-medium modifications of the nucleon-nucleon interaction. A softening of the pion mode and a possibility of the pion condensation are included. The nucleon pairing is incorporated. In the shear viscosity we include the lepton contribution calculated with account of the Landau damping in the photon exchange, the nucleon contribution described by the medium-modified one pion exchange, and other terms, such as the novel phonon contribution in the 1S$_0$ superfluid neutron phase, and the neutrino term in the neutrino opacity region. The nucleon shear viscosity depends on the density rather moderately and proves to be much less than the lepton term. Among the terms contributing to the bulk viscosity, the term from the medium modified Urca reactions possesses strongest density dependence because of the pion softening. Contributions to the bulk viscosity arising from other reactions induced by charged weak currents are included. The radiative bulk viscosity induced by charged and neutral weak currents in the region of the neutrino transparency of the star is also calculated with account for in-medium effects. The computed frequency boundary of the $r$-mode stability for the stars with the mass $\ge 1.8 M_{\odot}$ proves to be above the frequencies of all rotating young pulsars. To explain the stability of rapid rotation of old pulsars in X-ray binaries we propose a novel efficient mechanism associated with appearance of condensates of low-lying modes of bosonic excitations with finite momentum and/or with an enhancement of the inhomogeneous pion/kaon condensates in some parts of the star, if the angular velocity exceeds a critical value.

Final-state interactions in deep-inelastic scattering from a tensor polarized deuteron target

Deep-inelastic scattering (DIS) from a tensor polarized deuteron is sensitive to possible non-nucleonic components of the deuteron wave function. To accurately estimate the size of the nucleonic contribution, final-state interactions (FSIs) need to be accounted for in calculations. We outline a model that, based on the diffractive nature of the effective hadron-nucleon interaction, uses the generalized eikonal approximation to model the FSIs in the resonance region, taking into account the proton-neutron component of the deuteron. The calculation uses a factorized model with a basis of three resonances with mass W < 2 GeV as the relevant set of effective hadron states entering the final-state interaction amplitude for inclusive DIS. We present results for the tensor asymmetry observable Azz for kinematics accessible in experiments at Jefferson Lab and Hermes. For inclusive DIS, sizeable effects are found when including FSIs for Bjorken x > 0.2, but the overall size of Azz remains small. For tagged spectator DIS, FSIs effects are largest at spectator momenta around 300 MeV and for forward spectator angles.

Muon capture on the deuteron and3He

We plan to investigate the role of meson exchange currents in the description of the μ − + d → νμ + n + n and μ − + 3 He → νμ + 3 H reactions. They both are treated as the decay of the corresponding muonic atoms, with the muon initially on the lowest K shell. The muon binding energy in these atoms can be safely neglected and in the initial state we deal essentially with the deuteron (or 3 He) and muon at rest. These two reactions are interesting for several reasons. First of all, they offer a testing ground for the nuclear wave functions, which for any nucleon-nucleon (NN) and three-nucleon (3N) forces can be constructed for such light systems with great accuracy. In these reactions few-nucleon weak current operators are an important dynamical ingredient. In the current operators apart from the relatively well known single nucleon contributions, two-nucleon parts (generated by various meson exchanges) play an important role. Their details are not well known and several models should be considered. We present our formalism for dealing with these reactions and a simple method for partial wave decomposition of the two-nucleon operators. The crucial nuclear matrix elements of the corresponding weak current operators will be calculated in the momentum space and using partial wave decomposition. The effect of meson exchanges will be investigated in the energy spectrum of the emitted neutrinos (in the deuteron case) and in the total decay rates for the two reactions. We will employ various models of NN and 3N forces, such as the Bonn B or chiral NNLO potentials. Our results with the single nucleon currents look already very promising and we hope for the improvement in the description of the experimental data, when dominant two-nucleon current operators are included in our framework.

Application of Thomas–Reiche–Kuhn sum rule to construction of advanced dispersion models

The classical f-sum rule is generalized using quantum mechanical Thomas–Reiche–Kuhn sum rule to include nucleonic contribution, i.e. lattice vibrations. The sum rule is formulated for the transition strength function defined as a continuous condensed-matter equivalent of the oscillator strength known for discrete transitions in atomic spectra. The application of such formulated sum rule allows construction of dispersion models containing a fitting parameter directly related to the atomic density of material. The dielectric response expressed using the transition strength function is split into individual contributions such as direct and indirect electronic interband transitions including excitonic effect, excitations of electrons to the high-energy states existing above the conduction band, core-electron excitations and phonon absorption. The presented models reflect understanding of structure of disordered and crystalline materials on the basis of quantum theory of solids. The usual term ‘joint density of states’, that should be used only for electronic transitions in the one-electron approximation, is replaced by the more general term ‘transition density’.

Cooling of the neutron star in Cassiopeia A

We demonstrate that the high-quality cooling data observed for the young neutron star in the supernova remnant Cassiopeia A over the past 10 years--as well as all other reliably known temperature data of neutron stars--can be comfortably explained within the "nuclear medium cooling" scenario. The cooling rates of this scenario account for medium-modified one-pion exchange in dense matter and polarization effects in the pair-breaking formations of superfluid neutrons and protons. Crucial for the successful description of the observed data is a substantial reduction of the thermal conductivity, resulting from a suppression of both the electron and nucleon contributions to it by medium effects. We also find that possibly in as little as about ten years of continued observation, the data may tell whether or not fast cooling processes are active in this neutron star.

Two-boson exchange corrections to parity-violating elastic electron-proton scattering

Details of the calculation of two-boson exchange effects in parity-violating elastic $\mathit{ep}$ scattering within a simple hadronic model, including both the nucleon and the $\ensuremath{\Delta}(1232)$-resonance intermediate states, are presented. We examine the sensitivity of our results with respect to choice of form factors. We emphasize the importance of using correct relations relating $N\ensuremath{\rightarrow}\ensuremath{\Delta}$ and $\ensuremath{\Delta}\ensuremath{\rightarrow}N$ transition vertex functions. The $N\ensuremath{\Delta}$ Coulomb quadrupole transition is found to play an important role at higher ${Q}^{2}\ensuremath{\geqslant}3.0$ GeV${}^{2}$. We also elucidate the relation between our results and the well-known result on the $\ensuremath{\gamma}Z$-boson exchange effect given by Marciano and Sirlin. The effect of the nucleon contribution ${\ensuremath{\delta}}_{N}$ to parity asymmetry ${A}_{\mathrm{PV}}$ is found to be, in general, larger than the corresponding $\ensuremath{\Delta}$ contribution ${\ensuremath{\delta}}_{\ensuremath{\Delta}}$ except at extreme forward angles. Corrections to the extracted values of the strange form factors ${G}_{E}^{s}+\ensuremath{\beta}{G}_{M}^{s}$ from the HAPPEX, A4, and G0 data are also presented. The total TBE corrections to the extracted values of ${G}_{E}^{s}+\ensuremath{\beta}{G}_{M}^{s}$ in recent HAPPEX, G0, and A4 experiments are, depending on kinematics, found to be small except in a few cases where they range from $\ensuremath{-}20.6%$ to $48.3%$.

Hadro- and photo-production of η″ in quasi-free proton and neutron processes

The η″ photoproduction process on quasi-free proton and neutron and the reaction NN → η η″NN are investigated within a relativistic effective Lagrangian approach to hadronic interactions. Resonances with spins 1/2 and 3/2 are considered together with the nucleonic and t-channel meson-exchange current contributions. In photoproduction processes, the S11 resonance is found to be responsible for the sharp rise of the cross sections near threshold. In pp → η η″pp, it is found that the S11 resonance dominates the total cross section over the entire energy region considered. The spin observables, in particular the beam and target asymmetries, are shown to be very sensitive to the reaction mechanism and will help impose more stringent constraints on the model parameters.

Photoabsorption off nuclei with self-consistent vertex corrections

We study photoproduction off nuclei based on a self-consistent and covariant many-body approach for the pion and isobar propagation in infinite nuclear matter. For the first time the t-channel exchange of an in-medium pion is evaluated in the presence of vertex correction effects consistently. In particular the interference pattern with the s-channel in-medium nucleon and isobar exchange contribution is considered. Electromagnetic gauge invariance is kept as a consequence of various Ward identities obeyed by the computation. Adjusting the set of Migdal parameters to the data set we predict an attractive mass shift for the isobar of about 50 MeV at nuclear saturation density.