Stopping In Collisions Research Articles

Investigation of collective radial expansion and stopping in heavy ion collisions at Fermi energies

We present an analysis of multifragmentation events observed in central $\text{Xe}+\text{Sn}$ reactions at Fermi energies. Performing a comparison between the predictions of the stochastic mean-field (SMF) transport model and experimental data, we investigate the impact of the compression-expansion dynamics on the properties of the final reaction products. We show that the amount of radial collective expansion, which characterizes the dynamical stage of the reaction, influences directly the onset of multifragmentation and the kinematic properties of multifragmentation events. For the same set of events, we also undertake a shape analysis in momentum space, looking at the degree of stopping reached in the collision, as proposed in recent experimental studies. We show that full stopping is achieved for the most central collisions at Fermi energies. However, considering the same central event selection as in the experimental data, we observe a similar behavior of the stopping power with the beam energy, which can be associated with a change of the fragmentation mechanism, from statistical to prompt fragment emission.

Mid-rapidity antibaryon-to-baryon ratios in pp and Pb–Pb collisions measured by the ALICE experiment

Abstract Measurement of the antibaryon-baryon ratios ( B ¯ / B ) at mid rapidity probes the baryon transport and the degree of baryon stopping in high-energy collisions, providing insight into the collision dynamics. In this paper, we discuss the measurement of different B ¯ / B ratios ( p ¯ / p , Λ ¯ / Λ , Ξ ¯ + / Ξ − ) in pp collisions at s = 0.9 , 2.76 , and 7 TeV and in Pb–Pb collisions at s NN = 2.76 TeV , as a function of charged particle multiplicity, rapidity and transverse momentum. Results from pp and Pb–Pb collisions are presented and compared to models.

Optimizing the rapidity limit for nuclear stopping in intermediate energy heavy-ion collisions

A systematic study regarding the role of participant matter and spectator matter in nuclear stopping using isospin-dependent quantum molecular dynamics model is presented. The simulations have been carried out with soft equation of state along with the reduced isospin-dependent cross section to study the effect of different types and sizes of rapidity distributions on nuclear stopping for the whole colliding geometry with density-dependent symmetry energy. In addition to that, we attempt to investigate the role of isospin in heavy-ion collisions by calculating the individual contribution of neutrons and protons in nuclear stopping for different systems having different isotopic content.

Optimizing the Rapidity Limit for Nuclear Stopping in Intermediate Energy Heavy-Ion Collisions

Optimizing the Rapidity Limit for Nuclear Stopping in Intermediate Energy Heavy-Ion Collisions

Unified description of nuclear stopping in central heavy-ion collisions from 10A MeV to 1.2AGeV

The detailed analysis of wide excitation function of nuclear stopping has been studied within a transport model, Isospin-dependent Quantum Molecular Dynamics model (IQMD) and an overall good agreement with the INDRA and FOPI experimental data has been achieved. It is found that mean value of isotropy in central Heavy-Ion Collision (HIC) reaches a minimum near Fermi energy and approaches a maximum around 300 - 400$A$ MeV. This suggests that, in statistical average, the equilibration is far from being reached even in central HIC especially near Fermi energy. A hierarchy in stopping of fragments, which favors heavy fragments to penetrate, provides a robust restriction on the global trend of nuclear stopping and could serve as a probe for nuclear equation of state.

Probing the equation of state of asymmetric nuclear matter with isospin diffusion and stopping in heavy-ion collisions

Results from the study of isospin asymmetric Sn+Sn collisions at E/A=35 MeV and 50 MeV, collected with the LASSA and the Chimera detectors at the NSCL of MSU, respectively, are shown. The diffusion of neutrons and protons between projectiles and targets with different N/Z-asymmetries is studied by means of imbalance ratios measurements. The obtained results and their comparison to transport model simulations provide constraints on the density dependence of the symmetry energy. The systematic study of these phenomena at different impact parameters also allows us to explore isospin transparency and stopping phenomena in more central collisions, with important implications about the attainment of chemical equilibrium in central collisions at 35 MeV/nucleon.

Stability of the fragments and thermalization at the peak centre-of-mass energy

We simulated the central reactions of nearly symmetric and asymmetric systems, for energies at which maximum production of intermediate mass fragments (IMFs) occurred ( $E_{\rm c.m.}^{\rm peak}$ ). This study was carried out using hard EOS along with Cugnon cross-section employing MSTB method for clusterization. We studied the various properties of fragments. The stability of fragments was checked through persistence coefficient and gain term. The information about the thermalization and stopping in heavy-ion collisions was obtained via relative momentum, anisotropy ratio and rapidity distribution. We found that for a complete stopping of incoming nuclei very heavy systems are required. The mass dependence of various quantities (such as average and maximum central density, collision dynamics as well as the time zone for hot and dense nuclear matter) was also presented. In all cases (i.e., average and maximum central density, collision dynamics as well as the time zone for hot and dense nuclear matter) a power-law dependence was obtained.

THE STUDY OF COLLECTIVE FLOW AND BARYON STOPPING OF RELATIVISTIC HEAVY-ION COLLISIONS IN THE AGS, SPS, RHIC AND LHC ENERGY REGIONS

We study the features of baryon stopping and collective flow in relativistic heavy-ion collisions at energies reached at the CERN Large Hadron Collider (LHC), BNL Relativistic Heavy Ion Collider (RHIC), CERN Super Proton Synchrotron (SPS) and BNL Alternating Gradient Synchrotron (AGS) with the model of Non-Uniform Flow Model (NUFM) in this paper. The dependencies of the features of baryon stopping and collective flow on the collision energies are investigated.

Erratum: Transport model study of nuclear stopping in heavy-ion collisions over the energy range from0.09Ato160AGeV [Phys. Rev. C81, 034913 (2010)

Erratum: Transport model study of nuclear stopping in heavy-ion collisions over the energy range from<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>0.09</mml:mn><mml:mi>A</mml:mi></mml:mrow></mml:math>to<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>160</mml:mn><mml:mi>A</mml:mi></mml:mrow></mml:math>GeV [Phys. Rev. C<b>81</b>, 034913 (2010)

Study of Nuclear Stopping in Central Collisions at Intermediate Energies

Nuclear stopping has been investigated in central nuclear collisions at intermediate energies by analyzing kinematically complete events recorded with the help of the 4π multidetector INDRA for a large variety of symmetric systems. It is found that the mean isotropy ratio defined as the ratio of transverse to parallel momenta (energies) reaches a minimum near the Fermi energy, saturates or slowly increases depending on the mass of the system as the beam energy increases, and then stays lower than unity, showing that significant stopping is not achieved even for the heavier systems. Close to and above the Fermi energy, experimental data show no effect of the isospin content of the interacting system. A comparison with transport model calculations reveals that the latter overestimates the stopping power at low energies.

Baryon stopping in heavy-ion collisions at [formula omitted

It is argued that the experimentally observed baryon stopping may indicate (within the present experimental uncertainties) a non-monotonous behaviour as a function of the incident energy of colliding nuclei. This can be quantified by a midrapidity reduced curvature of the net-proton rapidity spectrum. The above non-monotonous behaviour reveals itself as a “zig-zag” irregularity in the excitation function of this curvature. The three-fluid dynamic calculations with a hadronic equation of state (EoS) fail to reproduce this irregularity. At the same time, the same calculations with an EoS involving a first-order phase transition into the quark–gluon phase do reproduce this “zig-zag” behaviour, however only qualitatively.

Transport model study of nuclear stopping in heavy-ion collisions over the energy range from0.09Ato160A GeV

Nuclear stopping in heavy-ion collisions over a beam energy range from SIS and AGS up to SPS is studied in the framework of the modified Ultrarelativistic Quantum Molecular Dynamics transport model, in which mean field potentials of both formed and ``preformed'' hadrons (from string fragmentation) and medium-modified nucleon-nucleon elastic cross sections are considered. It is found that nuclear stopping is influenced by both the stiffness of the equation of state and medium modifications of nucleon-nucleon cross sections at SIS energies. At high SPS energies, a two-bump structure is shown in the experimental rapidity distribution of free protons, which can be understood by considering the preformed hadron potentials.

Baryon stopping and saturation physics in relativistic collisions

We investigate baryon transport in relativistic heavy-ion collisions at energies reached at the CERN Super Proton Synchrotron, BNL Relativistic Heavy-Ion Collider (RHIC), and CERN LHC in the model of saturation. An analytical scaling law is derived within the color glass condensate framework based on small-coupling QCD. Transverse momentum spectra, net-baryon rapidity distributions and their energy, mass and centrality dependences are well described. In a comparison with RHIC data in Au + Au collisions at sqrt (s_NN) = 62.4 GeV and 200 GeV, the gradual approach to the gluon saturation regime is investigated, and limits for the saturation-scale exponent are determined. Predictions for net-baryon rapidity spectra and the mean rapidity loss in central Pb + Pb collisions at LHC energies of sqrt (s_NN) = 5.52 TeV are made.

Nuclear stopping and compression in heavy-ion collisions at intermediate energies

The nuclear stopping and the radial flow are investigated with an isospin-dependent quantum molecular dynamics (IQMD) model for Ni+Ni and Pb+Pb from 0.4 to and 1.2 GeV/u. The expansion velocity as well as the degree of nuclear stopping are higher in the heavier system at all energies. The ratio between the flow energy and the total available energy in center of mass of the colliding systems exhibits a positive correlation to the degree of nuclear stopping. The maximum density (ρmax) achieved in the compression is comparable to the hydrodynamics prediction only if the non-zero collision time effect is taken into account in the later. Due to the partial transparency, the growing of the maximum density achieved in the central region of the fireball with the increase of beam energy becomes gradually flat in the 1 GeV/u energy regime.

From RHIC to LHC: a relativistic diffusion approach

We investigate stopping and particle production in heavy-ion collisions in a Relativistic Diffusion Model (RDM). Using three sources for particle production, the energy- and centrality dependence of rapidity distributions of net protons, and pseudorapidity distributions of charged hadrons in heavy systems at RHIC energies are precisely reproduced in the analytical model. The transport coefficients are then extrapolated from Au + Au at RHIC energies (OsNN=19.6 - 200 GeV) to Pb + Pb at LHC energies of OsNN= 5.52 TeV. Rapidity distributions for net protons, and pseudorapidity spectra for produced charged particles are obtained and discussed in a three-sources model at LHC energies.

From RHIC to LHC: A relativistic diffusion approach

Stopping and particle production in heavy-ion collisions are investigated in a Relativistic Diffusion Model (RDM). Using three sources for particle production, the energy- and centrality dependence of rapidity distributions of net protons, and pseudorapidity distributions of charged hadrons in heavy systems at RHIC energies are precisely reproduced in the analytical model. The gradual approach to local thermal equilibrium is discussed. The transport coefficients are then extrapolated from Au + Au at RHIC energies ( s N N = 19.6 − 200 GeV ) to Pb + Pb at LHC energies of s N N = 5.52 TeV . Rapidity distributions fot net protons, and pseudorapidity spectra for produced charged particles are obtained and discussed in a three-sources model at LHC energies.

Baryon Stopping in pA Collisions

We calculate the inclusive small- x valence quark production cross section in proton-nucleus collisions at high energies. The calculation is performed in the framework of the Color Glass Condensate formalism. First we calculate the cross section in the quasi-classical approximation and then we include the the effects of double logarithmic reggeon evolution and leading logarithmic gluon evolution in the obtained cross section.

Editorial:John Wiley &amp; Sons, 1807–2007: 200 years success in publishing

We investigate the energy dependence of stopping and hadron production in high-energy heavy-ion collisions based on a three-sources Relativistic Diffusion Model. The transport coefficients are extrapolated from Au + Au and Cu + Cu at RHIC energies ( = 19.6–200 GeV) to Pb + Pb at LHC energies = 5.52 TeV. Rapidity distributions for net protons, and pseudorapidity spectra for produced charged particles in central collisions are compared to data at RHIC energies, and discussed for several extrapolations to LHC energies.

From fusion to total disassembly: Global stopping in heavy-ion collisions

Using the quantum molecular dynamics model, we aim to investigate the emis- sion of light complex particles, and degree of stopping reached in heavy-ion colli- sions. We took incident energies between 50 and 1000 MeV/nucleon. In addition, central and peripheral collisions and different masses are also considered. We ob- serve that the light complex particles act in almost similar manner as anisotropic ratio. In other words, multiplicity of light complex particles is an indicator of global stopping in heavy-ion collisions. We see that maximum light complex particles and stopping is obtained for heavier masses in central collisions.

Stopping and Baryon Transport in Heavy Ion Reactions

In this report I will give an experimental overview on nuclear stopping in hadron collisions, and relate observations to understanding of baryon transport. Baryon number transport is not only evidenced via net-proton distributions but also by the enhancement of strange baryons near mid-rapidity. Although the focus is on high-energy data obtained from pp and heavy ions from RHIC, relevant data from SPS and ISR will be considered. A discussion how the available data at higher energy relates and gives information on baryon junction, quark-diquark breaking will be made.