Investigation Of The Short-range Correlation And Its Induced High-momentum Tail By Using Heavy-ion Reactions

The nucleon-nucleon short-range correlations(SRCs)in nuclei and its influence on the momentum distribution of nucleons are hot issues,which have been studied extensively in recent years.The traditional shell model holds that the nucleons in a nu-clear system move independently in the mean-field created by their mutually interac-tions,thus the momentum of a nucleon cannot exceed the Fermi momentum(k<kp).However,the subsequent proton knocking experiments indicate that only 60-70%of the nucleons obey this independent particle motion,which is obviously not consistent with the shell model picture.The high-energy electron-scattering experiment has re-cently pointed out that the isospin-dependent nucleon-nucleon SRC pairs are universal in nuclei.The form of the SRC pairs are proton-neutron correlation,proton-proton cor-relation and neutron-neutron correlation,where proton-neutron correlation is in domi-nant(np-dominance).These SRC pairs induced by the tensor force have large relative momentum and small centre-of-mass momentum,which push some nucleons from low momenta(k<kF)to high momenta(k>kF),creating a high-momentum tail(HMT)in nucleon momentum distribution.The SRC and its induced HMT have significant effects on many problems in nuclear structure and nuclear astrophysics,such as the nu-clear symmetric energy,the structure and equation of state of neutron stars,where the related subjects are being studied.Based on the current experimental and theoretical progress in SRC physics,within the framework of IBUU model,we shall study the SR-C and its induced HMT by using heavy-ion reactions.Via comparing and analyzing the calculated results of the model with and without incorporation of the HMT,we acquire the sensitive observable of the SRC-induced HMT.The specific work is as follows:Firstly,we introduce the microcosmic transport models that descript the intermediate energy heavy-ion collision in chapter 2.In chapter 3,according to the experimental facts and theoretical researches,such as the protons have larger probability than neutrons to have momenta higher than the Fermi momentum due to the SRC in neutron-rich nuclei,recent theories and experi-ments have suggested that the HMT of nuclear momentum distribution decreases as C/k4 and the approximately linear-relationship beween high-momentum component of nuclear momentum distribution and isospin asymmetry calculated by microscopic approaches and phenomenological models.We thus obtain the parameterized form of the nucleon momentum distribution of nuclear matter with the nucleon-nucleon S-RC effect considered.Then the nucleon momentum distribution in finite nuclei has been calculated based on the local density approximation,we further add the high-momentum distribution into the IBUU model.The calculated results show that an obvious high-momentum component appeared in the nuclear momentum distribution when taking the SRC effect into account.In chapter 4,based on the IBUU model with incorporation of the HMT,we have simulated the reactions of symmetric system 12C+12C and asymmetric one 124Sn+124Sn at beam energies of 50 MeV/nucleon and 140 MeV/nucleon.We show that the effect of HMT can lead to an obvious increase of both high-energy free proton and neutron emission,the probability of high-energy nucleon emission increases with the growth of incident beam energy,but the effect of HMT on the high-energy nucleon emission becomes weaker at higher incident beam energy due to the fact that the S-RC of nucleons in the nucleus becomes less important in nucleon-nucleon collisions with the beam energy increasing.To study the effect of HMT on the proton-neutron bremsstrahlung photon emission,we also simulate the reactions of 124Sn+124Sn,112Sn+112Sn and 197Au+197Au based on the IBUU transport model.We found the proton-neutron bremsstrahlung photons are sensitive to the high-momentum component in nucleon momentum distribution,and the HMT can lead to an obvious increase of hard photon production of neutron-rich nuclei.It is also seen that the difference about the effect of HMT on the bremsstrahlung photon production is relatively obvious for the different mean-field potentials,because the nucleons would subject to different forces under different mean-fields potentials,thus their momenta in different mean-fields are naturally different.Since photon production results mainly from the n-p collisions,so the photon production is different for the different mean-fields potentials.To reduce the uncertainties such as the photon production probability and NN scattering cross sec-tion as well as the systematic error,the ratios of double differential photon production for same systems with different beam energies Rp and for different systems with same beam energies Rp' are proposed as possible probes to study the SRC and its induced HMT of nuclei.The nuclear symmetric energy is also a hot topic,because of its important influ-ence on the heavy-ion nuclear reaction,the equation of state of asymmetric nuclear matter as well as the nuclide synthesis and the structure and evolution of neutron stars in the field of astrophysics.Based on the IBUU model with incorporation of the HMT,we also discuss and analyze the possibility of using proton-neutron bremsstrahlung photon as the sensitive probe of symmetric energy.In chapter 5,we simulate the re-actions of 132Sn+124Sn and 40Ca+40Ca at beam energy of 50 MeV/nucleon,the production of bremsstrahlung photons and its sensitivity to the nuclear balance energy are studied in the cases of with and without HMT considered.From the small differ-ence of spectra of bremsstrahlung photons between stiffer(x=0)and softer(x=1)symmetry energies in both FFG and HMT cases,we conclude that the photon yield may be not a sensitive probe of the nuclear symmetry energy,regardless of whether or not the HMT of nucleon momentum distribution is taken into account.However,the ratio of two reactions is not only sensitive to the HMT but also the symmetry energy,and the effect of HMT can even enhance the relative sensitivity of hard photon on the symmetry energy.This is possible because the ratio reduces the influence of the medi-um effect and the difference caused by the photon production probability,which makes the effect of symmetry energy of photon production appear.In addition,we notice that the ratio R in the HMT case is smaller than that in FFG case.This is because the HMT is predominantly induced by the proton-neutron correlations,which leads to the effect of HMT on the photons emission become weaker with the increase of isospin asymmetry ?.Finally,in last chapter,we summarize the work,and some outlooks on possible working directions in the future are present.