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Register a new userEffect of energy conservation on in-medium $mbox{NN}to mbox{N}Delta$ cross section in isospin-asymmetric nuclear matter
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In this paper, the in-medium $NNrightarrow NDelta$ cross section is calculated in the framework of the one-boson exchange model by including the isovector mesons, i.e. $delta$ and $rho$ mesons. Due to the isospin exchange in the $NNrightarrow NDelta$ process, the vector self-energies of the outgoing particles are modified relative to the incoming particles in isospin asymmetric nuclear matter, and it leads to the effective energies of the incoming $NN$ pair being different from the outgoing $NDelta$ pair. This effect is investigated in the calculation of the in-medium $NNrightarrow NDelta$ cross section. With the corrected energy conservation, the cross sections of the $Delta^{++}$ and $Delta^+$ channels are suppressed, and the cross sections of the $Delta^0$ and $Delta^-$ channels are enhanced relative to the results obtained without properly considering the potential energy changes. Our results further confirm the dependence of medium correction factor, $R=sigma_{ NNrightarrow NDelta}^*/sigma_{NNrightarrow NDelta}^{text{free}}$, on the charge state of $NNrightarrow NDelta$ especially around the threshold energy, but the isospin splitting of medium correction factor $R$ becomes weak at high beam energies.
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The in-medium $NNrightarrow NDelta$ cross section and its differential cross section in isospin asymmetric nuclear medium are investigated in the framework of the one-boson exchange model by including the isovector mesons, i.e., $delta$ and $rho$ mesons. Our results show that the in-medium $NNrightarrow NDelta$ cross sections are suppressed with density increasing, and the differential cross sections become isotropic with the density increasing at the beam energy around the $Delta$ threshold energy. The isospin splitting on the medium correction factor, $R=sigma_{ NNrightarrow NDelta}^*/sigma_{NNrightarrow NDelta}^{text{free}}$ is observed for different channels of $NNto NDelta$, 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.
Within the one boson exchange model, $Delta$-mass dependent M-matrix and its influence on the calculation of $NDelta to NN$ cross sections are investigated. Our calculations show that the $m_{Delta}$ dependence of $|textbf{p}_{NDelta}|$ and $|mathcal{M}|^2$ has effects on the calculations of $sigma_{NDeltato NN}$, especially around the threshold energy. We finally provide a table of accurate $sigma_{NDeltato NN}$ which can be used in the transport models.
This paper presents measurements of production cross sections and inelastic cross sections for the following reactions: 60 GeV/$c$ protons with C, Be, Al targets and 120 GeV/$c$ protons with C and Be targets. The analysis was performed using the NA61/SHINE spectrometer at the CERN SPS. First measurements were obtained using protons at 120 GeV/$c$, while the results for protons at 60 GeV/$c$ were compared with previously published measurements. These interaction cross section measurements are critical inputs for neutrino flux prediction in current and future accelerator-based long-baseline neutrino experiments.
We explore the influence of in-medium nucleon-nucleon cross section, symmetry potential and impact parameter on isospin sensitive observables in intermediate-energy heavy-ion collisions with the ImQMD05 code, a modified version of Quantum Molecular Dynamics model. At incident velocities above the Fermi velocity, we find that the density dependence of symmetry potential plays a more important role on the double neutron to proton ratio $DR(n/p)$ and the isospin transport ratio $R_i$ than the in-medium nucleon-nucleon cross sections, provided that the latter are constrained to a fixed total NN collision rate. We also explore both $DR(n/p)$ and $R_i$ as a function of the impact parameter. Since the copious production of intermediate mass fragments is a distinguishing feature of intermediate-energy heavy-ion collisions, we examine the isospin transport ratios constructed from different groups of fragments. We find that the values of the isospin transport ratios for projectile rapidity fragments with $Zge20$ are greater than those constructed from the entire projectile rapidity source. We believe experimental investigations of this phenomenon can be performed. These may provide significant tests of fragmentation time scales predicted by ImQMD calculations.
The proton-proton momentum correlation function from different rapidity regions are systematically investigated for the Au + Au collisions at different impact parameters and different energies from 400$A$ MeV to 1500$A$ MeV in the framework of the isospin-dependent quantum molecular dynamics model complemented by the $Lednickacute{y}$ and $Lyuboshitz$ analytical method. In particular, in-medium nucleon-nucleon cross section dependence of the correlation function is brought into focus, while the impact parameter and energy dependence of the momentum correlation function are also explored. The sizes of the emission source are extracted by fitting the momentum correlation functions using the Gaussian source method. We find that the in-medium nucleon-nucleon cross section obviously influence the proton-proton momentum correlation function which is from the whole rapidity or projectile/target rapidity region at smaller impact parameters, but there is no effect on the mid-rapidity proton-proton momentum correlation function, which indicates that the emission mechanism differs between projectile/target rapidity and mid-rapidity protons.
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