Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMaximum Azimuthal Anisotropy of Neutrons from Nb-Nb Collisions at 400 AMeV and the Nuclear Equation of State
142
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We measured the first azimuthal distributions of triple--differential cross sections of neutrons emitted in heavy-ion collisions, and compared their maximum azimuthal anisotropy ratios with Boltzmann--Uehling--Uhlenbeck (BUU) calculations with a momentum-dependent interaction. The BUU calculations agree with the triple- and double-differential cross sections for positive rapidity neutrons emitted at polar angles from 7 to 27 degrees; however, the maximum azimuthal anisotropy ratio for these free neutrons is insensitive to the size of the nuclear incompressibility modulus K characterizing the nuclear matter equation of state.
rate research
Read More
Triple-differential cross sections for neutrons from high-multiplicity La-La collisions at 250 and 400 MeV per nucleon and Nb-Nb collisions at 400 MeV per nucleon were measured at several polar angles as a function of the azimuthal angle with respect to the reaction plane of the collision. The reaction plane was determined by a transverse-velocity method with the capability of identifying charged-particles with Z=1, Z=2, and Z > 2. The flow of neutrons was extracted from the slope at mid-rapidity of the curve of the average in-plane momentum vs the center-of-mass rapidity. The squeeze-out of the participant neutrons was observed in a direction normal to the reaction plane in the normalized momentum coordinates in the center-of-mass system. Experimental results of the neutron squeeze-out were compared with BUU calculations. The polar-angle dependence of the maximum azimuthal anisotropy ratio $r(theta)$ was found to be insensitive to the mass of the colliding nuclei and the beam energy. Comparison of the observed polar-angle dependence of the maximum azimuthal anisotropy ratio $r(theta)$ with BUU calculations for free neutrons revealed that $r(theta)$ is insensitive also to the incompressibility modulus in the nuclear equation of state.
We measured neutron triple-differential cross sections from multiplicity-selected Au-Au collisions at 150, 250, 400, and 650 AMeV. The reaction plane for each collision was estimated from the summed transverse velocity vector of the charged fragments emitted in the collision. We examined the azimuthal distribution of the triple-differential cross sections as a function of the polar angle and the neutron rapidity. We extracted the average in--plane transverse momentum $langle P_xrangle$ and the normalized observable $langle P_x/P_perprangle$, where $P_perp$ is the neutron transverse momentum, as a function of the neutron center-of-mass rapidity, and we examined the dependence of these observables on beam energy. These collective flow observables for neutrons, which are consistent with those of protons plus bound nucleons from the Plastic Ball Group, agree with the Boltzmann--Uehling--Uhlenbeck (BUU) calculations with a momentum--dependent interaction. Also, we calculated the polar-angle-integrated maximum azimuthal anisotropy ratio R from the value of $langle P_x/P_perprangle$.
The Equation of State (EoS) of dense matter represents a central issue in the study of compact astrophysical objects and heavy ion reactions at intermediate and relativistic energies. We have derived a nuclear EoS with nucleons and hyperons within the Brueckner-Hartree-Fock approach, and joined it with quark matter EoS. For that, we have employed the MIT bag model, as well as the Nambu--Jona-Lasinio (NJL) and the Color Dielectric (CD) models, and found that the NS maximum masses are not larger than 1.7 solar masses. A comparison with available data supports the idea that dense matter EoS should be soft at low density and quite stiff at high density.
Transport simulations are very valuable for extracting physics information from heavy-ion collision experiments. With the emergence of many different transport codes in recent years, it becomes important to estimate their robustness in extracting physics information from experiments. We report on the results of a transport code comparison project. 18 commonly used transport codes were included in this comparison: 9 Boltzmann-Uehling-Uhlenbeck-type codes and 9 Quantum-Molecular-Dynamics-type codes. These codes have been required to simulate Au+Au collisions using the same physics input for mean fields and for in-medium nucleon-nucleon cross sections, as well as the same initialization set-up, the impact parameter, and other calculational parameters at 100 and 400 AMeV incident energy. Among the codes we compare one-body observables such as rapidity and transverse flow distributions. We also monitor non-observables such as the initialization of the internal states of colliding nuclei and their stability, the collision rates and the Pauli blocking. We find that not completely identical initializations constitute partly for different evolutions. Different strategies to determine the collision probabilities, and to enforce the Pauli blocking, also produce considerably different results. There is a substantial spread in the predictions for the observables, which is much smaller at the higher incident energy. We quantify the uncertainties in the collective flow resulting from the simulation alone as about $30%$ at 100 AMeV and $13%$ at 400 AMeV, respectively. We propose further steps within the code comparison project to test the different aspects of transport simulations in a box calculation of infinite nuclear matter. This should, in particular, improve the robustness of transport model predictions at lower incident energies where abundant amounts of data are available.
Relativistic heavy ion collisions, which are performed at large experimental programs such as Relativistic Heavy Ion Colliders (RHIC) STAR experiment and the Large Hadron Colliders (LHC) experiments, can create an extremely hot and dense state of the matter known as the quark gluon plasma (QGP). A huge amount of sub-nucleonic particles are created in the collision processes and their interaction and subsequent evolution after the collision takes place is at the core of the understanding of the matter that builds up the Universe. It has recently been shown that event-by-event fluctuations in the spatial distribution between different collision events have great impact on the particle distributions that are measured after the evolution of the created system. Specifically, these distributions are greatly responsible for generating the observed azimuthal anisotropy in measurements. Furthermore, the eventual cooling and expansion of the fluctuating system can become very complex due to lumps of energy density and temperature, which affects the interaction of the particles that traverse the medium. In this configuration, heavy flavor particles play a special role, as they are generally created at the initial stages of the process and have properties that allow them to retain memory from the interactions within the whole evolution of the system. However, the comparison between experimental data and theoretical or phenomenological predictions on the heavy flavor sector cannot fully explain the heavy quarks coupling with the medium and their subsequent hadronization process. [Full abstract in file]
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
