New approach to intranuclear cascades with quantum Monte Carlo configurations

We propose a novel semiclassical approach to intranuclear cascades, which takes as input quantum Monte Carlo nuclear configurations and uses a semiclassical, impact-parameter-based algorithm to model the propagation of protons and neutrons in the nuclear medium. We successfully compare our simulations to available proton-carbon scattering data and nuclear-transparency measurements. By analyzing the dependence of the simulated observables upon the ingredients entering our intranuclear cascade algorithm, we provide a quantitative understanding of their impact. Particular emphasis is devoted to the role played by nuclear correlations, the Pauli exclusion principle, and interaction probability distributions.

Figure 1

Schematics of a propagating nucleon (black circle). The distance traveled by the propagating nucleon is depicted by a black arrow. The crosses represent background nucleons. An interaction test would be performed for the nucleon in red.

Figure 2

The proposed algorithm for the INC model.

Figure 3

Nucleon density in carbon from Green's function Monte Carlo (red) and mean-field (blue) configurations.

Figure 4

Proton-proton (top) and proton-neutron (bottom) correlation functions in carbon from Green's function Monte Carlo (red) and mean field (blue) configurations.

Figure 5

Distribution of distance traveled (blue histogram) by 500 MeV test nucleons traveling through a 0.16 nucleons/${\mathrm{fm}}^3$ background density of nucleons at rest, fixed interaction cross section of 50 mb, and using the Gaussian interaction probability. The black and orange lines are the expected distributions for the fitted (1.23 fm) and expected (1.25 fm) values of the mean-free path, respectively.

Figure 6

Proton-carbon scattering total cross section as a function of the incoming proton kinetic energy. In the top panel the entire energy range for which experimental data are available is shown. In the bottom panel the low-energy region is magnified. The red and blue curves correspond to the cylinder algorithm where the mean-field (MF) and quantum Monte Carlo (QMC) configurations have been used, respectively. The green and orange curves are the same but for the Gaussian interaction probability. The results displayed in purple refers to the mean-free path (MFP) calculations. The solid and dashed curves corresponds to the use of the GEANT4 [65] and NASA [66] parametrization of the cross section in the interaction probability, respectively. The data points are from Ref. [72]

Figure 7

Carbon transparency as a function of the proton kinetic energy. The different curves indicate different approaches used as described in Fig. 6. The experimental data are taken from Refs. [4, 6, 7, 75, 76, 77].

Figure 8

Left: a schematic picture of an external proton scattering off the nucleus. The distance from the proton to the center of the nucleus is $r_1$, and the propagation step is $d\ell$. The radius of the cylinder is given by $\sqrt{\sigma /\pi }$ where $\sigma$ is the interaction cross section between the proton and a background particle; $d\ell$ is also the height of the cylinder. Right: same as for the left, but for a nucleon kicked inside the nucleus. This follows what is done in the nuclear transparency event simulations.

Figure 9

The four panels corresponds to histograms of the distance traveled by a struck particle before the first interaction takes place for different values of the interaction cross section. The results in blue and red correspond to MF and QMC initial nucleon configurations, respectively. For each of the panels we also report the fixed cross section used, the total number of events generated, and the number of hits for each configuration.

Figure 10

Nucleon multiplicity, defined as the number of nucleons that exit the nucleus in a simulation setup similar to nuclear transparency. These distributions are obtained using quantum Monte Carlo configurations with (solid red) and without (solid green) formation zone, as well as using mean-field configurations with (dashed blue) and without (dashed orange) formation zone. The inset displays the same distribution but in a linear scale.

Figure 11

Comparison between the two interaction models used within the intranuclear cascade model. The geant model is based on the SAID database [64] and obtained using geant4 [65] and the NASA model is given from Ref. [66].