In the framework of the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model, effect of the momentum dependence of nuclear symmetry potential on pion-/pion+ ratio in the neutron-rich reaction 132Sn+124Sn at a beam energy of 400 MeV/nucleon is studied. We find that the momentum dependence of nuclear symmetry potential affects the compressed density of colliding nuclei, numbers of produced pion- and pion+, as well as the value of pion-/pion+ ratio. The momentum dependent nuclear symmetry potential increases the compressed density of colliding nuclei, numbers of produced resonances delta(1232), N*(1440), pion- and pion+, as well as the value of pion-/pion+ ratio.
Nuclear modification factor ($R_{cp}$) of protons and pions are investigated by simulating Au + Au collisions from 0.8 to 1.8$A$ GeV in a framework of an isospin-dependent quantum molecular dynamics (IQMD) model. $R_{cp}$ of protons rises with the increase of \pt~ at different beam energies owing to radial flow and Cronin effect. The rate of increase of \rcp~ is suppressed at higher beam energies. The significant difference of $R_{cp}$ between protons and pions indicates different medium effects between protons and pions. By changing the in-medium nucleon-nucleon cross section, the $R_{cp}$ of…
In this paper we presented a short review of radioactive halos as from the perspective of their interpretation as integral record in time of different kind of known or unknown radioactivities. A special attention is paid for the unified interpretation of the supergiant halos (SGH), discovered by Grady, Walker and Laemlein, as integral record of pion emission during fission.
Generalized mesonic Super-Čerenkov Radiations (SČR) are investigated. The energy behavior of the pionic refractive index in the low energy pionic SCR-sector is presented. We estimated that the true coherent SCR-pion emission is possible mainly in the SCRS-energy bands 190-315 MeV for all pions; 910-960 MeV only for positive pions, and 80-1000 GeV for all pions, in certain nuclear reactions. We predicted that SČR-pionic band will be enlarged for the pion energies higher than 80 GeV. The strong correlations between angle of SCR-pion emission and (meson and projectile)-energies are evidentiated. …
Within the framework of the isospin-dependent Boltzmann-Uehling-Uhlenbeck(IBUU) transport model, we studied the effects of the pion potential and the symmetry energy on the pion production in the central $^{197}Au+^{197}Au$ collisions around the pion production threshold. It is found that the pion potential has opposite effects on the value of $π^-/π^+$ ratio at low and high pion energies. The effect of the pion potential on the total $π^-/π^+$ ratio becomes larger in heavy-ion collisions at beam energies below the pion production threshold. And at beam energies below the pion production thres…
Using the light-front pion wave function based on a Bethe-Salpeter amplitude model, we study the properties of the pion in symmetric nuclear matter. The pion model we adopt is well constrained by previous studies to explain the pion properties in vacuum. In order to consistently incorporate the constituent up and down quarks of the pion immersed in symmetric nuclear matter, we use the quark-meson coupling model, which has been widely applied to various hadronic and nuclear phenomena in a nuclear medium with success. We predict the in-medium modifications of the pion lectromagnetic form factor,…
Resonance states below pion-nucleon threshold and their consequences for nuclear systems
在π介子产生阈值以下的pp--> p pi ^+ X和pd--> ppX_1反应中，在丢失的质谱中观察到了有规律的窄峰序列。它们在文献中被解释为超窄轻双重子，或核子共振，或轻介子与处于基态的核子形成共振态的表现。我们讨论了这种奇异态的存在如何影响核系统的性质。我们表明，中子星的结构是急剧变化的所有三种情况。我们发现，在存在重子或核子共振时，中子星的最大可能质量将小于观测极限。轻π介子的存在与观测到的中子星质量并不矛盾。轻π介子允许存在任意大小的扩展核物体，由强电磁力约束。
The saturation properties of the nuclear matter taking pion correlations into account is studied. We construct a Bogoliubov transformations for the pion pair operators and calculate the energy associated with the pion pairs. The pion dispersion relation is investigated. We next study the correlation energy due to one pion exchange in nuclear matter and neutron matter at random phase approximation using the generator coordinate method. The techniques of the charged pion correlations are discussed in the neutron matter calculations. We observe that there is no sign of the pion condensation in th…
Exploring the nuclear pion dispersion relation through the anomalous coupling of photon to photon and neutral pion
本文研究了通过γ- γ' π_0反应中的反常耦合测量核物质中π色散关系的可能性。结果表明，这种反应允许研究类空动量的π介子模式。如果π介子在核物质中由于与δ-空穴态的混合而软化，则这种反应的显著强度预计将移动到类空间区域。竞争的背景过程进行了评估，并得出结论，可以通过实验获得有用的见解，但只有通过一个困难的独家测量。
The charge form factor and weak decay constant of the pion as well as the pion-quark coupling constant in symmetric nuclear matter are explored in the framework of the Nambu--Jona-Lasinio model, where the pion is described as a bound state of dressed quark-antiquark pair obtained by the Bethe-Salpeter equation. For the in-medium current quark properties, we adopt the quark-meson coupling model, which describes successfully many hadron properties in a nuclear medium. The pion decay constant and the pion-quark coupling constant are found to decrease with increasing density as well as the magnitu…
The structure and electroweak properties of the pion in symmetric nuclear matter are presented in the framework of the Nambu--Jona-Lasinio model. The pion is described as a bound state of a dressed quark-antiquark pair governed by the Bethe-Salpeter equation. For the in-medium current-light-quark properties we use the quark-meson coupling model, which describes successfully the properties of hadron in a nuclear medium. We found that the light-quark condensates, the pion decay constant and pion-quark coupling constant decrease with increasing nuclear matter density. We then predict the modifica…
Based on the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model and the scaling model according to nucleon effective mass, effects of elastic and inelastic NN scattering cross sections on pion-/pion+ in the neutron-rich reaction of Ca48+Ca48 at a beam energy of 400 MeV/nucleon are studied. It is found that cross-section effects of both NN elastic and inelastic scatterings affect Delta_1232, pion- and pion+ production, as well as the value of pion-/pion+.
Using results from the chiral perturbation theory for the s-wave interaction and the delta-resonance model for the p-wave interaction of pions with nucleons, we have evaluated the spectral functions of pions in asymmetric nuclear matter with unequal proton and neutron densities. We find that in hot dense neutron-rich matter the strength of the spectral function of positively charged pion at low energies is somewhat larger than that of negatively charged pion. In a thermal model, this isospin-dependent effect slightly reduces the ratio of negatively charged to positively charged pions that are …
Using the relativistic Vlasov-Uehling-Uhlenbeck (RVUU) equation based on mean fields from the nonlinear relativistic models, we study the effect of medium modification of pion production threshold on the total pion yield and the $π^-/π^+$ ratio in Au+Au collisions. We find that the in-medium threshold effect enhances both the total pion yield and the $π^-/π^+$ ratio, compared to those without this effect. Furthermore, including the medium modification of the pion production threshold in asymmetric nuclear matter leads to a larger $π^-/π^+$ ratio for the $NLρδ$ model with a stiffer symmetry ene…
Three instances are discussed in which results produced by chiral perturbation theory can be reliably pushed to high space-like values of transferred momenta: 1. nuclear interactions, 2. nucleon sigma-term and 3. space-like structure of the pion
The high-density behavior of nuclear symmetry energy is among the most uncertain properties of dense neutron-rich matter. Its accurate determination has significant ramifications in understanding not only the reaction dynamics of heavy-ion reactions especially those induced by radioactive beams but also many interesting phenomena in astrophysics, such as the explosion mechanism of supernova and the properties of neutron stars. The heavy-ion physics community has devoted much effort during the last few years to constrain the high-density symmetry using various probes. In particular, the pion-/p…
Within a transport model, we study effects of the momentum dependence of nuclear symmetry potential on pion observables in central Sn + Sn collisions at 270 MeV/nucleon. To this end, a quantity $U_{sym}^{\infty}(ρ_{0})$, i.e., the value of nuclear symmetry potential at the saturation density $ρ_{0}$ and infinitely large nucleon momentum, is used to characterise the momentum dependence of nuclear symmetry potential. It is shown that with a certain $L$ (i.e., slope of nuclear symmetry energy at $ρ_{0}$) the characteristic parameter $U_{sym}^{\infty}(ρ_{0})$ of symmetry potential affects signific…
Bremsstrahlung of photons emitted during the scattering of $π^{+}$-mesons off nuclei is studied for the first time. Role of interactions between $π^{+}$-mesons and nuclei in the formation of the bremsstrahlung emission is analyzed in details. We discover essential contribution of emitted photons from nuclear part of Johnson-Satchler potential to the full spectrum, in contrast to the optical Woods-Saxon potential. We observe unusual essential influence of the nuclear part of both potentials on the spectrum at high photon energies. This phenomenon opens a new experimental way to study and check …
Covariant and self consistent vertex corrections for pions and isobars in nuclear matter
我们评估的π介子和同量异位素传播子在冷核物质自洽应用同量异位素空穴模型的协变形式。Migdal的顶点校正效应被认为是系统的现象学软形状因子的情况下。饱和核物质用核子的标量和矢量平均场来模拟。结果表明，π N δ顶点的短程修整对π介子和同量异位素性质有显著影响。使用现实的参数集，我们预测约50兆电子伏的Delta共振核饱和密度的向下移动。的pionic软模式是不太明显，比以前的研究。
Pion-induced Drell-Yan processes are proposed as a potential tool to measure the flavor dependence of the EMC effect, that is, the flavor-dependent modification of quark distributions in the nuclear medium. Existing pionic Drell-Yan data are compared with calculations using a recent model for nuclear quark distributions that incorporates flavor-dependent nuclear effects. While no firm conclusions can yet be drawn, we demonstrate that existing Drell-Yan data seem to imply a flavor dependence of the EMC effect. We highlight how pion-induced Drell-Yan experiments on nuclear targets can access imp…
Despite the success of modern nuclear parton distribution functions (nPDFs) in describing nuclear hard-process data, they still suffer from large uncertainties. One of the poorly constrained features is the possible asymmetry in nuclear modifications of valence $u$ and $d$ quarks. We study the possibility of using pion-nucleus Drell-Yan dilepton data as a new constraint in the global analysis of nPDFs. We find that the nuclear cross-section ratios from the NA3, NA10 and E615 experiments can be used without imposing significant new theoretical uncertainties and, in particular, that these datase…
Two- and three-pion correlation functions are investigated for a source that is not fully chaotic. Various models are examined to describe the source. The chaoticity and weight factor are evaluated in each model as measures of the strength of correlations and compared to experimental results. A new measure of three-pion correlation is also suggested.
Dynamics of the nuclear fragmentations and the charge exchange reactions in pion-nucleus collisions near the $Δ$(1232) resonance energies has been investigated within the Lanzhou quantum molecular dynamics (LQMD) transport model. An isospin, momentum and density-dependent pion-nucleon potential is implemented in the model, which influences the pion dynamics, in particular the kinetic energy spectra, but weakly impacts the fragmentation mechanism. The absorption process in pion-nucleon collisions to form the $Δ$(1232) resonance dominates the heating mechanism of target nucleus. The excitation e…
Within the framework of a thermal model with its parameters fitted to the results from an isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model, we study the pion in-medium effect on the charged-pion ratio in heavy-ion collisions at various energies. We find that due to the cancellation between the effects from pion-nucleon s-wave and p-wave interactions in nuclear medium, the π^-/π^+ ratio generally decreases after including the pion in-medium effect. The effect is larger at lower collision energies as a result of narrower pion spectral functions at lower temperatures.
Within the framework of semiclassical Boltzmann-Uehling-Uhlenbeck (BUU) transport model, we investigated the effects of symmetry energy on the sub-threshold pion using the isospin MDI interaction with the stiff and soft symmetry energies in the central collision of $^{48}$Ca + $^{48}$Ca at the incident beam energies of 100, 150, 200, 250 and 300 MeV/nucleon, respectively. We find that the ratio of $π^{-}/π^{+}$ of sub-threshold charged pion production is greatly sensitive to the symmetry energy, particularly around 100 MeV/nucleon energies. Large sensitivity of sub-threshold charged pion produ…
