Mass In Nuclear Matter Research Articles

Bayesian inference on isospin splitting of nucleon effective mass from giant resonances in 208Pb * *Supported in part by the National Natural Science Foundation of China (11905302, 11625521) and National SKA Program of China (2020SKA0120300)

From a Bayesian analysis of the electric dipole polarizability, the constrained energy of isovector giant dipole resonance, the peak energy of isocalar giant quadrupole resonance, and the constrained energy of isocalar giant monopole resonance in 208Pb, we extract the isoscalar and isovector effective masses in nuclear matter at saturation density as and , respectively, at 90% confidence level. The constraints obtained on and lead to a positive isospin splitting of nucleon effective mass in asymmetric nuclear matter of isospin asymmetry at as . In addition, the symmetry energy at the subsaturation density is determined to be MeV at 90% confidence level.

Near-threshold J/ψ-meson photoproduction on nuclei

On the basis of the first-collision model that relies on the nuclear spectral function and which includes incoherent processes involving charmonium production in proton–nucleon collisions, the photoproduction of J/ψ mesons on nuclei is considered at energies close to the threshold for their production on a nucleon. The absorption of final J/ψ mesons, their formation length, and the binding and Fermi motion of target nucleons are taken into account in this model along with the effect of the nuclear potential on these processes. The A dependences of the absolute and relative charmonium yields are calculated together with absolute and relative excitation functions under various assumptions on the magnitude of the cross section for J/ψN absorption, the J/ψ-meson formation length, and their inmedium modification. It is shown that, at energies above the threshold, these features are virtually independent of the formation length and the change in the J/ψ-meson mass in nuclear matter but are rather highly sensitive to the cross section for J/ψN interaction. The calculations performed in the present study can be used to determine the unknown cross section for J/ψ-meson absorption in nuclei from a comparison of their results with data expected from experiments in the Hall C of the CEBAF (USA) facility upgraded to the energy of 12 GeV. It is also shown that the absolute and relative excitation functions for J/ψ mesons in photon–nucleus reactions at subthreshold energies are sensitive to the change in the meson mass and, hence, carry information about the properties of charmonium in nuclear matter.

Isospin splitting of the nucleon effective mass from giant resonances inPb208

Based on mean field calculations with Skyrme interactions, we extract a constraint on the isovector effective mass in nuclear matter at saturation density $\rho_0$, i.e., $m_{v}^{\ast}(\rho_0)=(0.77\pm0.03) m$ by combining the experimental data of the centroid energy of the isovector giant dipole resonance (IVGDR) and the electric dipole polarizability $\alpha_{\mathrm{D}}$ in $^{208}$Pb. Meanwhile, the isoscalar effective mass at $\rho_0$ is determined to be $m_{s}^{\ast}(\rho_0)=(0.91\pm0.05) m$ by analyzing the measured excitation energy of the isoscalar giant quadrupole resonance (ISGQR) in $^{208}$Pb. From the constrained $m_{s}^{\ast}(\rho_0)$ and $m_{v}^{\ast}(\rho_0)$, we obtain the isospin splitting of nucleon effective mass in asymmetric nuclear matter of isospin asymmetry $\delta$ at $\rho_0$ as $[m_n^{\ast}(\rho_0,\delta)-m_p^{\ast}(\rho_0,\delta)]/m = \Delta m^*_1(\rho_0) \delta + O(\delta^3)$ with the linear isospin splitting coefficient $\Delta m^*_1(\rho_0) = 0.33\pm0.16$. We notice that using the recently corrected data on the $\alpha_{\mathrm{D}}$ in $^{208}$Pb with the contribution of the quasideuteron effect subtracted slightly enhances the isovector effective mass to $m_{v}^{\ast}(\rho_0)=(0.80\pm0.03) m$ and reduces the linear isospin splitting coefficient to $\Delta m^*_1(\rho_0) = 0.27\pm0.15$. Furthermore, the constraints on $m_{v}^{\ast}(\rho)$, $m_{s}^{\ast}(\rho)$ and $\Delta m^*_1(\rho)$ at other densities are obtained from the similar analyses and we find that the $\Delta m^*_1(\rho)$ increases with the density.

Measurement of neutral-meson masses in meson-nucleus interactions at a momentum of 7 GeV/c at the Hyperon-M setup

The π 0, η, K 0, ω, and f 2(1270) masses were measured at the HYPERON-Msetup in meson-nucleus interactions at a momentum of 7 GeV/c by using six nuclear targets: Be, C, Al, Cu, Sn, and Pb. The experiment in question proved to be insensitive to the expected effects of a modification to the omega-meson mass in nuclear matter. As for the f 2(1270) meson, its mass and width values averaged over all experimental data, $$m_{f_2 }$$ = 1275.8 ± 1.0(stat.) ± 0.4(syst.) MeV/c 2 and $$\Gamma _{f_2 }$$ = 190.3 ± 1.9(stat.) ± 1.8(syst.) MeV/c 2, agree well with the world-average values. At the same time, our experimental data do not rule out the possible effect of an in-medium modification to the f 2(1270)-meson mass for heavy nuclei at a level better than 0.4%.

η' meson under partial restoration of chiral symmetry in nuclear medium

We shed light upon the η' mass in nuclear matter in the context of partial restoration of chiral symmetry, pointing out that the UA(1) anomaly effects causes the η'-η mass difference necessarily through the chiral symmetry breaking. As a consequence, it is expected that the η' mass is reduced by order of 100 MeV in nuclear matter where partial restoration of chiral symmetry takes place. The discussion given here is based on Ref. [1]

Momentum dependence of the symmetry potential and its influence on nuclear reactions

A Skyrme-type momentum-dependent nucleon-nucleon force distinguishing isospin effect is parameterized and further implemented in the Lanzhou Quantum Molecular Dynamics (LQMD) model for the first time, which leads to a splitting of nucleon effective mass in nuclear matter. Based on the isospin- and momentum-dependent transport model, we investigate the influence of momentum-dependent symmetry potential on several isospin-sensitive observables in heavy-ion collisions. It is found that symmetry potentials with and without the momentum dependence but corresponding to the same density dependence of the symmetry energy result in different distributions of the observables. The mid-rapidity neutron/proton ratios at high transverse momenta and the excitation functions of the total $\pi^{-}/\pi^{+}$ and $K^{0}/K^{+}$ yields are particularly sensitive to the momentum dependence of the symmetry potential.

A study of Λ hypernuclei within the Skyrme–Hartree–Fock model

We investigate the properties of the single Lambda hypernuclei within a Skyrme-Hartree-Fock (SHF) model. The parameters of the Skyrme type effective lambda-nucleon (Lambda N) interaction are obtained by fitting to the experimental Lambda binding energies of hypernuclei with masses spanning a wide range of the periodic table. Alternative parameter sets are also obtained by omitting nuclei below mass number 16 from the fitting procedure. The SHF calculations are performed for the binding energies of the Lambda single-particle states over a full mass range using the best fit parameter sets obtained in these fitting procedures and the results are compared with the available experimental data. The data show some sensitivity to the parameter sets obtained with or without including the nuclei below mass 16. The radii of the Lambda orbits in the hypernuclear ground states and the Lambda effective mass in nuclear matter show some dependence on different parameter sets. We present results for the total binding energy per baryon of the hypernuclei over a large mass region to elucidate their stability as a function of the baryon number. We have also employed the our best fit Lambda N parameter sets to investigate the role of hyperons in some key properties of neutron stars.

Effective Photon Mass in Nuclear Matter and Finite Nuclei

Electromagnetic field in nuclear matter and nuclei are studied. In the nuclear matter, because the expectation value of the electric charge density operator is not zero, different in vacuum, the U(1) local gauge symmetry of electric charge is spontaneously broken, and consequently, the photon gains an effective mass through the Higgs mechanism. An alternative way to study the effective mass of photon is to calculate the self-energy of photon perturbatively. It shows that the effective mass of photon is about 5.42 MeV in the symmetric nuclear matter at the saturation density ρ0 = 0.16 fm -3 and about 2.0 MeV at the surface of 238U. It seems that the two-body decay of a massive photon causes the sharp lines of electron–positron pairs in the low energy heavy ion collision experiments of 238 U + 232 Th .

The ( π−, γγ) reaction in nuclei and the σ meson in the medium

A theoretical analysis of the ( π −, γγ) reaction in nuclei is made in order to find the viability of this reaction to test modifications of the σ meson mass in nuclear matter. The ππ correlation in the scalar–isoscalar channel in nuclear matter could, in principle, manifest itself in this reaction since it plays an important role in the ππ→ γγ mechanism. But we conclude that this effect is hardly visible in this reaction due to the strong background of the pion-bremsstrahlung terms. Only with some special cuts and for some polarization states are the effect visible at the cost of a strong reduction in the cross section.

Charmonium mass in nuclear matter

The mass shift of charmonium states in nuclear matter is studied in the perturbative QCD approach. The leading-order effect due to the change of gluon condensate in nuclear matter is evaluated using the leading-order QCD formula, while the higher-twist effect due to the partial restoration of chiral symmetry is estimated using a hadronic model. We find that while the mass of $J/\ensuremath{\psi}$ in nuclear matter decreases only slightly, those of $\ensuremath{\psi}(3686)$ and $\ensuremath{\psi}(3770)$ states are reduced appreciably. Experimental study of the mass shift of charmonium states in nuclear matter can thus provide valuable information on the changes of the QCD vacuum in nuclear medium.

Pionic decay of a possible dibaryon d’ and quark models of πB and πd’ couplings

The pionic decay of a possible dibaryon, d’ → πNN, is studied in the model assuming the production of 3P0 quark-antiquark pairs and in other models of effective quark-pion coupling. The vertex constants and the form factors for pion-baryon and pion-dibaryon couplings are calculated. The effect of the internal pion structure on decay widths is investigated. It is shown that the quark structure of the nucleon-nucleon wave function in the overlap region plays an important role in dibaryon decays, and known models of nucleon-nucleon interaction are analyzed with allowance for this circumstance. The decay width of a dibaryon is estimated as a function of its effective mass in nuclear matter.

On the determination of the pion effective mass in nuclei from pionic atoms

The binding energies of the deeply bound 1s and 2p states in pionic atoms of $^{207}$Pb, recently established experimentally in the $^{208}$Pb(d,$^3$He) reaction, have been used by several groups to derive the pion effective mass in nuclear matter. We show that these binding energies are fully consistent with `normal' pionic atoms and that the real part of the pion-nucleus potential at the center of $^{207}$Pb is 28$\pm$3 MeV and not 20 MeV as suggested previously.

Skyrme-Hartree-Fock treatment ofΛandΛΛhypernuclei withG-matrix motivated interactions

Skyrme-like hyperon-nucleon potentials are derived from $G$-matrix calculations and shown to reproduce well the $\ensuremath{\Lambda}$ single-particle spectra of hypernuclei measured at BNL and KEK. Previously known potentials are reexamined systematically. The fit of the spectra can restrict the radii of $\ensuremath{\Lambda}$ orbits in hypernuclear ground states, $\ensuremath{\Lambda}$ well depth and effective mass in nuclear matter, and polarization of nuclear cores caused by hyperon rather tightly. The implications of the $\ensuremath{\Lambda}N$ spin-orbit force to the spectra are considered. Hartree-Fock calculations of binding energies of ${}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}^{13}$B with density-dependent $G$-matrix $\ensuremath{\Lambda}\ensuremath{\Lambda}$ potentials are presented, taking note of the core-rearrangement effects induced by $\ensuremath{\Lambda}N$ interactions.

Pauli Nonlocality in Heavy-Ion Rainbow Scattering: A Further Test of the Folding Model

Nonlocal interactions are an intrinsically quantum phenomenon. In this work we point out that, in the context of heavy ions, such interactions can be studied through the refractive elastic scattering of these systems at intermediate energies. We show that most of the observed energy dependence of the local equivalent bare potential arises from the exchange nonlocality. The nonlocality parameter extracted from the data was found to be very close to the one obtained from folding models. The effective mass of the colliding, heavy-ion, system was found to be close to the nucleon effective mass in nuclear matter.

Composite nucleons in scalar and vector mean fields.

We emphasize that the composite structure of the nucleon may play quite an important role in nuclear physics. It is shown that the momentum-dependent repulsive force of second order in the scalar field, which plays an important role in Dirac phenomenology, can be found in the quark-meson coupling (QMC) model, and that the properties of nuclear matter are well described through the quark-scalar density in a nucleon and a self-consistency condition for the scalar field. The difference between theories of point-like nucleons and composite ones may be seen in the change of the $\omega$-meson mass in nuclear matter if the composite nature of the nucleon suppresses contributions from nucleon-antinucleon pair creation.

-Meson in Nuclear Matter

$\phi$-meson mass in nuclear matter ($m_{\phi}^*$) is investigated using an effective Lagrangian of $\phi$ interacting with octet baryons. $m_{\phi}^*$ decreases by a few \% in nuclear matter due to the current conservation and effective nucleon/hyperon masses. Its implication to the p-A and A-A collisions are briefly discussed.

S-wave meson-nucleon interactions and the meson mass in nuclear matter from chiral effective lagrangians

Chiral effective lagrangians may differ in their prediction of meson-nucleon scattering amplitudes off-meson-mass-shell, but must yield identical S-matrix elements. We argue that the effective meson mass in nuclear matter obtained from chiral effective lagrangians is also unique. Off-mass-shell amplitudes obtained using the PCAC choice of pion field must therefore not be viewed as fundamental constraints on the dynamics, the determination of the effective meson mass in nuclear matter or the possible existence of meson condensates in the ground state of nuclear matter. This hypothesis is borne out by a calculation of the effective mass in two commonly employed formulations of chiral perturbation theory which yield different meson-nucleon scattering amplitudes off-meson-mass-shell.

The omega -meson mass in nuclear matter with a density-dependent relativistic NN interaction

The omega -meson mass in nuclear matter has been deduced from the omega propagator in which the coupling to the polarization of the Fermi and Dirac seas has been taken into account. This polarization has been calculated in the RPA approximation. For this calculation a density-dependent relativistic NN interaction reproducing the saturation curve of a Dirac-Brueckner calculation providing a good description of nuclear matter has been used.

Medium effects on subthreshold kaon production in heavy-ion collisions.

The relativistic transport model is extended to include the kaon degree of freedom. We also take into account the density dependence of the kaon effective mass in nuclear matter and the rescattering of kaons by nucleons. We find that the inclusion of kaon self-energy due to the attractive scalar mean field leads to an enhanced kaon yield in heavy-ion collisions at subthreshold energies. Also, kaon rescatterings are found to affect significantly the final kaon momentum spectra. We compare the theoretical results with recent experimental data from the Heavy-Ion Synchrotron (SIS) at GSI.

LOCV calculations of pressure in nuclear matter at finite temperature

The lowest-order constrained variational method is used to calculate the equation of state of hot nuclear matter. The calculations are performed for a wide range of densities of interest in heavy-ion collisions and astrophysics. A realistic nuclear Hamiltonian that contains N-N and N- Delta interactions and fits N-N scattering as well as nuclear matter saturation data is used. Besides spin, isospin, total angular momentum and density dependence, the correlation functions are also arranged to depend on the temperature of the system. The liquid-vapour phase equilibrium, as well as the behaviour of the effective mass in nuclear matter, is discussed.