A New Calculation of the In-Medium Quark Condensate at Finite Density and Temperature

The in-medium quark condensate is studied with an equivalent-mass approach in which one does not need to make assumptions on the derivatives of model parameters with respect to the quark current mass.It is shown that the condensate is generally a decreasing function of both the density and temperature with the decreasing speed depending on the confinement parameter.Specially,at given density,the condensate decreases on increasing temperature.The decreasing speed is comparatively small at lower temperature,and becomes very fast at higher temperature.

Pion Decay Constant and Masses of Light Quarks and In-medium Goldstone Bosons

Based on the fully dressed confining quark propagator, the pion decay constant fπ, local quark vacuum condensate, and the masses of light quarks and in-medlum Goldstone bosons are investigated. The pion decay constant fπ is predicted and compared with its value of experimental measurement. A great agreement is obtained. With the predicted fπ and values of Goldstone boson masses measured by experiments in free configuration the current masses of light quarks and the masses of in-medium Goldstone bosons are obtained.

1-3 Nuclear In-medium Effects of Strange Particles in Proton-nucleus Collisions

Extraction of the in-medium properties of strange particles from heavy-ion collisions is very complicated, since he nuclear density varies in the evolution of nucleus-nucleus collisions. To avoid the uncertainties of the baryon ensities during the stage of strange particle production, one can investigate proton-nucleus collisions where the uclear density is definite around the saturation density. Dynamics of strange particles produced in the protoninduced uclear the reactions near the threshold energies has been investigated within the Lanzhou quantum olecular dynamics (LQMD) transport model. The in-medium modifications on particle production in densenuclear matter are considered through the corrections to the elementary cross sections via the effective mass and he mean-field potentials[1].

In-medium NN→NΔ cross section and its dependence on effective Lagrange parameters in isospin-asymmetric nuclear matter

The in-medium NN→N△ cross sections and its differential cross sections in isospin asymmetric nuclear medium are investigated in the framework of the one-boson exchange model by including isovector mesons, i.e., δand p mesons. Our results show that the in-medium NN→N△ cross sections are suppressed when the density increases, and the differential cross sections become isotropic with an increase in the density around the △ threshold energy. The isospin splitting on the medium correction factor, R =σ_(NN→N△)~*/σ_(NN→N△)^(free) is observed for different channels of NN→N△, especially around the threshold energy for all the effective Lagrangian parameters. By analyzing the selected effective Lagrangian parameters, our results show that the larger effective mass is, the weaker medium correction R is.

Theoretical uncertainties on the extraction of in-medium NN cross sections by different Pauli blocking algorithms

Three typical Pauli blocking algorithms in quantum molecular dynamics type models are investigated in the nuclear matter,the nucleus,and heavy ion collisions.In nuclear matter,the blocking ratios obtained with the three algorithms are underestimated by 13%-25%compared to the corresponding analytical values.For a finite nucleus,spurious collisions occur around the surface of the nucleus owing to the defects of the Pauli blocking algorithms.In the simulations of heavy ion collisions,the uncertainty of stopping power arising from the different Pauli blocking algorithms is less than 5%.Furthermore,the in-medium effects of nucleon-nucleon(NN)cross sections on the nuclear stopping power are discussed.Our results show that the transport model calculations with free NN cross sections result in the stopping power decreasing with beam energy when the beam energy is less than 300 MeV/u.To increase or decrease the values of the stopping power,the transport model calculations need enhanced or suppressed model dependent in-medium NN cross sections that are expected to be smaller than the true in-medium NN cross sections.

Progress of quantum molecular dynamics model and its applications in heavy ion collisions

In this review article,we first briefty introduce the transport theory and quantum molecular dynamics model applied in the study of the heavy ion collisions from low to intermediate energies.The developments of improved quantum molecular dynamics model(ImQMD)and ultra-relativistic quantum molecular dynamics model(UrQMD),are reviewed.The reaction mechanism and phenomena related to the fusion,multinucleon transrer,fragmentation,collective flow and particle production are reviewed and discussed within the framework of the two models.The constraints on the isospin asymmetric muclear equation of state and in-medium nucleon nucleon cross sections by comparing the heavy ion collision data with transport models calculations in last decades are also discussed,and the uncertainties of these constraints are analyzed as well.Finally,we discuss the future direction of the development of the transport models for improving the understanding of the reaction mechanism,the descriptions of various observables,the constraint on the nuclear equation of state,as well as for the constraint on in-medium nucleon-nucleon cross sections.

Momentum dependence of pion-inducedφmeson production on nuclei near threshold

We study the near-threshold pion-induced production ofφmesons off nuclei in the kinematical conditions of the HADES experiment,recently performed at GSI.The calculations have been performed within a collision model based on the nuclear spectral function.The model accounts for both the primaryπ^-meson–protonπ^-p→φn and the secondary pion–nucleonπN→φNφproduction processes as well as the effects of the nuclearφand nucleon mean-field potentials.We find that the primary reaction channelπ^-p→φn dominates in theφproduction off 12C and^（184）W target nuclei in the HADES acceptance window at incident pion momentum of 1.7 Ge V/c.We calculate the momentum dependence of the absolute and relative（transparency ratio）φmeson yields from the above direct channel.The calculations have been performed for this initial pion momentum allowing for different options for theφN absorption cross sectionσ（φN ）and different scenarios for the in-medium mass shifts of theφmeson and secondary neutron,produced together withφin this channel.We demonstrate that the transparency ratio for theφmesons has,contrary to the absolute cross sections,an insignificant sensitivity to theφmeson and secondary neutron in-medium mass shifts atφmomenta studied in the HADES experiment.On the other hand,we show that there are measurable changes in the transparency ratio due to theφN absorption cross section,which means that such a relative observable can be useful to help determine this cross section from the data taken in the HADES experiment.

ηmesons in hot magnetized nuclear matter

ηN interactions are investigated in hot magnetized asymmetric nuclear matter using the chiral SU(3)model and chiral perturbation theory(ChPT).In the chiral modcl,thc in-medium properties of η-mesons are calcu-lated using medium modified scalar densities under the influence of an extermal magnetic field.Further,in a com-bined chiral model and ChPT approach,off-shell contributions of the ηN interactions are evaluated from the ChPTeffective ηN Lagrangian,and the in-medium effect of scalar densities are incorporated from the chiral SU(3)model.We find that the magnetic field has a significant effect on the in-medium mass and optical potential of η mesons,andwe observe a deeper mass-shift in the combined chiral model and ChPT approach than in the solo chiral SU(3)model.In both approaches,no additional mass-shift is observed due to the uncharged nature of η mesons in the presenceof a magnetic field.

Novel relativistic mean field Lagrangian guided by pseudo-spin symmetry restoration

The relativistic mean field(RMF)model has achieved great success in describing various nuclear phenomena.However,several serious defects are common.For instance,the pseudo-spin symmetry of high-l orbits is distinctly violated in general,leading to spurious shell closures N Z 58 and 92.This leads to problems in describing structure properties,including shell structures,nuclear masses,etc.Guided by the pseudo-spin symmetry restoration[Geng et al.,Phys.Rev.C,100:051301(2019)],a new RMF Lagrangian DD-LZ1 is developed by considering the density-dependent meson-nucleon coupling strengths.With the newly obtained RMF Lagrangian DD-LZ1,satisfactory descriptions can be obtained for the bulk properties of nuclear matter and finite nuclei.In particular,significant improvements on describing the single-particle spectra are achieved by DD-LZ1.In particular,the spurious shell closures Z 58 and 92,commonly found in previous RMF calculations,are eliminated by the new effective interaction DD-LZ1,and consistently the pseudo-spin symmetry(PSS)around the Fermi levels is reasonably restored for both low-l and high-l orbits.Moreover,the description of nuclear masses is also notably improved by DD-LZ1,as compared to the other RMF Lagrangians.

Near-threshold K^*(892)^+ meson production in the interaction of π−mesons with nuclei

We study the inclusive production of strange vector K^∗(892)^+ mesons in π−A reactions at near-threshold laboratory incident pion momenta of 1.4-2.0 GeV/c via a nuclear spectral function approach.The approach accounts for incoherent primary π−meson-proton π−p→K^∗(892)^+Σ^− production processes as well as the influence of the scalar K^∗(892)^+-nucleus potential(or the K^∗(892)^+ in-medium mass shift)on these processes.We calculate the absolute differential and total cross sections for the production of K∗(892)+mesons from carbon and tungsten nuclei at laboratory angles of 0∘-45∘and at the aforementioned momenta in five scenarios for the aforenoted shift.We show that the K^∗(892)^+ momentum distributions and their excitation functions(absolute and relative)possess a high sensitivity to changes in the in-medium K^∗(892)^+ mass shift in the low-momentum region of 0.1-0.6 GeV/c.Therefore,the measurement of such observables in a dedicated experiment at the GSI pion beam facility in the near-threshold momentum domain will allow us to get valuable information on the K^∗(892)^+ in-medium properties.