Based on the relativistic transport model ART with the hadronic equation of state extended to have a phase transition via the use of the MIT bag model, properties of phase transition of dense nuclear matter formed in relativistic heavy-ion collisions are investigated. Proton sideward and directed flows are calculated with different equation of states in Au + Au collisions at beam energies of 2, 4, 6 and 8 GeV/nucleon. Compared with AGS experimental data in existence, the boundary of first-order phase transition is roughly confined, i.e., in the range of 2.5-4 times saturation density with temperature about 64-94 MeV. Such constraints are useful for ongoing RHIC Beam Energy Scan-II program to study the QCD matter phase diagram.
Based on the Isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model, the in-medium nucleon-nucleon inelastic scattering ( which is dominated by pion production at low and intermediate energies) is explored. It is found that the in-medium modification of nucleon-nucleon inelastic scatterings appears to reduce the neutron to proton ratio n/p at higher kinetic energies. Although the in-medium modification of nucleon-nucleon inelastic scatterings, as expected, affects the value of $π^-/π^+$ ratio, considering a series of undetermined properties of delta resonance and $π$ in medium, t…
Motivated by the recent measurement of proton-proton spin-correlation parameters up to 2.5 GeV laboratory energy, we investigate models for nucleon-nucleon (NN) scattering above 1 GeV. Signatures for a gradual failure of the traditional meson model with increasing energy can be clearly identified. Since spin effects are large up to tens of GeV, perturbative QCD cannot be invoked to fix the problems. We discuss various theoretical scenarios and come to the conclusion that we do not have a clear phenomenological understanding of the spin-dependence of the NN interaction above 1 GeV.
Within a transport model we search for potential probes of the isospin dependence of the in-medium nucleon-nucleon (NN) cross sections. Traditional measures of the nuclear stopping power are found sensitive to the magnitude but they are ambiguous for determining the isospin dependence of the in-medium NN cross sections. It is shown that isospin tracers, such as the neutron/proton ratio of free nucleons, at backward rapidities/angles in nuclear reactions induced by radioactive beams in inverse kinematics is a sensitive probe of the isospin dependence of the in-medium NN cross sections. At forwa…
Status, open questions, and future prospects of the physics of excited nucleons are discussed. Emphasis is on the study of the structure of nucleons via measurements of their electromagnetic transition form factors, the search for "missing" resonances, the spin structure of the nucleon in the resonance region, and connections between the resonance and the deep-inelastic regimes.
An overview of recent results with CLAS is presented with emphasis on nucleon resonance studies, nucleon spin structure, and generalized parton distributions.
Producing kaon mesons in heavy-ion collisions at beam energies below their threshold energy is an important way to investigate the properties of dense nuclear matter. In this study, based on the newly updated version of the ultrarelativistic quantum molecular dynamics model, we introduce the kaon-nucleon (KN) potential, including both the scalar and vector (also dubbed Lorentz-like) aspects. We revisit the influence of the KN potential on the collective flow of K$^{+}$ mesons produced in Au+Au collisions at $E_{lab}$ = 1.5 GeV/nucleon and find that the contribution of the newly included Lorent…
In the framework of the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model, sensitive regions of some nucleon observables to the nuclear symmetry energy are studied. It is found that the symmetry energy sensitive observable n/p ratio in the $^{132}$Sn+$^{124}$Sn reaction at 0.3 GeV/nucleon in fact just probes the density-dependent symmetry energy below the density of $1.5ρ_0$ and effectively probes the density-dependent symmetry energy around or somewhat below the saturation density. Nucleon elliptic flow can probe the symmetry energy from the low-density region to the high-density …
The momentum distributions of pions and $ρ$-mesons in the nucleon are extracted from experiment. Perspectives of the quark microscopic theory of mesonic cloud are outlined.
We summarize recent progress in the studies of the short-rang correlations (SRC) in nuclei in high energy electron and hadron nucleus scattering and suggest directions for the future high energy studies aimed at establishing detailed structure of two-nucleon SRCs, revealing structure of three nucleon SRC correlations and discovering non-nucleonic degrees of freedom in nuclei.
Based on an isospin and momentum-dependent transport model, we studied the effect of momentum-dependent symmetry potential on the free neutron to proton ratio of preequilibrium nucleon emission. It is found that for $^{132}Sn+^{124}Sn$ reaction at 400 MeV/nucleon incident beam energy, free n/p ratio of preequilibrium nucleon emission mainly probe the momentum-dependence of symmetry potential at nucleon momentum around 400 $\sim$ 600 MeV/c. Whereas for 200 MeV/nucleon incident beam energy, this observable mainly probe the momentum-dependence of symmetry potential at nucleon momentum around 200 …
The effects of the symmetry potential and the isospin dependent in-medium nucleon-nucleon (NN) cross section on the number of proton(neutron) emissions N$_p(N_n$) are studied respectively within an isospin-dependent quantum molecular dynamics (IQMD) model. The isospin dependent in-medium NN cross section is found to have a strong influence on N$_p(N_n$) but N$_p(N_n$) is not sensitive to the symmetry potential for the neutron-deficient colliding system at relatively high energies.We propose to make use of the N$_p(N_n$) as a probe to extract information on the isospin dependent in-medium NN cr…
We study the possibility to constrain the hidden strangeness content of the nucleon by means of the polarization observables in phi meson electroproduction. We consider the OZI evading direct knockout mechanism that arises from the non-vanishing s\bar{s} sea quark admixture of the nucleon as well as the background of the dominant diffractive and the one-boson-exchange processes. Large sensitivity on the nucleon strangeness are found in several beam-target and beam-recoil double polarization observables. The small \sqrt{s} and W region, which is accesible at some of the current high-energy elec…
The nucleon resonances near 2 GeV are investigated through the $Σ$(1385) and $Λ(1520)$ photoproductions within a Regge-plus-resonance approach based on the new experimental data released by the CLAS Collaboration. The $Δ(2000)$ and the $N(2120)$ are found essential to reproduce the experimental data and should be assigned as second $[Δ5/2^+]$ and third $[N3/2^-]$ in the constituent quark model, respectively. A calculation of the binding energy and decay pattern supports that the $N(1875)$, which is listed in the PDG as the third $N3/2^-$ nucleon resonance instead of the $N(2120)$, is from the …
A comparison between full few-body Faddeev/Alt-Grassberger-Sandhas (Faddeev/AGS) and continuum-discretized coupled channels (CDCC) calculations is made for the resonant and nonresonant breakup of $^{11}$Be on proton target at 63.7 MeV/u incident energy. A simplified two-body model is used for $^{11}$Be which involves an inert $^{10}$Be(0$^+$) core and a valence neutron. The sensitivity of the calculated observables to the nucleon-nucleon potential dynamical input is analysed. We show that with the present NN and N-core dynamics the results remain a puzzle for the few-body problem of scattering…
This article is focused on the multiplicity and probability distribution of the emitted charged pions <N_π> for interaction of ^{84}Kr_{36} projectile with nuclear emulsion targets at kinetic energy 1 GeV per nucleon. In the wounded nucleon model frame work, we have calculated the total number of wounded nucleons (W) and total number of interactions (ν). The obtained results revealed that the average multiplicity of the charged pions <N_π> is dependent on the projectile and target mass. The calculated values of the wounded nucleons (W) and total number of interactions (ν) shows strong dependen…
We propose a means to detect the nucleon strange quark-antiquark asymmetry, which is predicted as a non-perturbative effect, but still unchecked directly by available experiments. The difference for the $D(c\bar{q})$ and $\bar{D}(\bar{c}q)$ meson production cross sections in neutrino and antineutrino induced charged current deep inelastic scattering is illustrated to be sensitive to the nucleon strange asymmetry. Prospect is given and the effect due to the light quark fragmentation is also discussed for the extraction of the strange asymmetry in future experiments.
Low-energy nuclear structure is not sensitive enough to resolve fine details of nucleon-nucleon (NN) interaction. Insensitivity of infrared physics to the details of short-range strong interaction allows for consistent, free of ultraviolet divergences, formulation of local theory at the level of local energy density functional (LEDF) including, on the same footing, both particle-hole as well as particle-particle channels. Major difficulty is related to parameterization of the nuclear LEDF and its density dependence. It is argued that structural simplicity of terminating or isomeric states offe…
We present a fully relativistic and gauge invariant framework for calculating the cross sections of dilepton production in nucleon-nucleon (NN) collisions which is based on the meson-exchange approximation for the NN scattering amplitudes. Predictions of our model are compared with those of other covariant models that have been used to describe this reaction. We discuss the comparison of our calculations with the old DLS and the recent HADES data.
Some of the recent attempts to detect signals of nucleon-nucleon correlations with semi-exclusive A(e,e'p) and exclusive A(e,e'pN) processes are reviewed. Unfactorized and distorted-wave calculations for these processes are discussed. The calculations implement two-body currents stemming from pion-exchange and intermediate $Δ$ excitation. The two-body currents are shown to be highly competitive with the mechanisms related to nucleon-nucleon correlations. This observation seriously hampers attempts to link semi-exclusive A(e,e'p) measurements, which probe high missing energies, to the correlate…
The momentum dependence of the medium modifications on nucleon-nucleon elastic cross sections is discussed with microscopic transport theories and numerically investigated with an updated UrQMD microscopic transport model. The semi-peripheral Au+Au reaction at beam energy $E_b=400A$ MeV is adopted as an example. It is found that the uncertainties of the momentum dependence on medium modifications of cross sections influence the yields of free nucleons and their collective flows as functions of their transverse momentum and rapidity. Among these observables, the elliptic flow is sensitively dep…
We summarize the measurements investigating the nucleon spin structure done at Jefferson Lab, a multi-GeV continuous electron beam facility located in Newport News, Virgina, USA. After motivating spin structure studies, we explain how Jefferson Lab uniquely contributes to them and describe the experimental program that was achieved with energies up to 6 GeV. We then discuss the continuation of this program at the higher energies now available thanks to the recent 12 GeV upgrade of Jefferson Lab's accelerator.
We investigate $ϕ$ meson electroproduction to probe the hidden strangeness content of the nucleon. We found that even a small amount of the $s\bar{s}$ admixture in the nucleon wavefunction can lead to a significant change in several double polarization asymmetries in $ϕ$ electroproduction, which can be tested experimentally at current electron facilities.
The effect of initial correlations between nucleons on the nuclear break-up mechanism is studied. A quantum transport theory which extends standard mean-field approach is developed to incorporate short range pairing correlation as well as direct nucleon-nucleon collisions. A time evolution of the nuclear break-up from a correlated system leading to the emission of two particles to the continuum is performed. We show that initial correlations have strong influence on relative angles between particles emitted in coincidence. The present qualitative study indicates that nuclear break-up might be …
We study the isospin effects of the mean field and two-body collision on the nucleon emissions at the intermediate energy heavy ion collisions by using an isospin dependent transport theory. The calculated results show that the nucleon emission number $N_{n}$ depends sensitively the isospin effect of nucleon nucleon cross section and weakly on the isospin dependent mean field for neutron-poor system in higher beam energy region . In particular, the correlation between the medium correction of two-body collision and the momentum dependent interaction enhances the dependence of nucleon emission …
We propose to use proton knockout reactions (p,2p) from a deeply bound orbit as a new probe into three-nucleon-force (3NF) effects. The remarkable advantage of using (p,2p) reaction is that we can choose an appropriate kinematical condition to probe the 3NF effects. We analyze (p,2p) reactions on a 40Ca target within the framework of distorted-wave impulse approximation with a g-matrix interaction based on chiral two- and three-nucleon forces. The chiral 3NF effects significantly change the peak height of the triple differential cross section of (p,2p) reaction. We also clarify the corresponde…
Within the key issues of hadronic physics one of the interesting issues in nuclear physics is whether there is a transition region between meson-nucleon and quark-gluon degrees of freedom in the NN interaction. This question is relevant for pairs of free nucleons as well as for nucleon pairs immersed in nuclear matter. From NN phase shifts we deduce a dibaryonic scale of 1 GeV for the soft core NN potential strengths at nucleon separation r equal 0.25 to 0.5 fm. A short range intermediate transition, with fusion and fission of the two scattered nucleons into a dibaryon with prevailing quark-gl…
I discuss the conditions under which the application of chiral perturbation theory to the NN potential gives reliable results for NN scattering phase shifts. ChiPT also yields a convergent expansion for the deuteron charge operator. For cutoffs < 1 GeV, this produces precise predictions for deuterium's quadrupole and charge form factors in the range Q^2 < 0.25 GeV^2.
We show that the strong dependence of the amplitude for $NN$ hard scattering on the collision energy can be used to magnify the effects of short range nucleon correlations in quasielastic $pd$ scattering. Under specific kinematical conditions the effect of initial and final state interactions can be accounted for by rescaling the cross section calculated within the plane wave impulse approximation. The feasibility to investigate the role of relativistic effects in the deuteron wave function is demonstrated by comparing the predictions of different formalisms. Binding effects due to short range…
We derive the cross-section for exclusive vector meson production in high energy deeply inelastic scattering off a deuteron target that disintegrates into a proton and a neutron carrying large relative momentum in the final state. This cross-section can be expressed in terms of a novel gluon Transition Generalized Parton Distribution (T-GPD); the hard scale in the final state makes the T-GPD sensitive to the short distance nucleon-nucleon interaction. We perform a toy model computation of this process in a perturbative framework and discuss the time scales that allow the separation of initial …
The description of electromagnetic interactions with hadrons from the quark level requires knowledge of the underlying quark-gluon ingredients. I discuss some properties of the quark-photon vertex and quark Compton vertex, along with the role of electromagnetic gauge invariance and vector-meson dominance. A simple parametrization for the quark-photon vertex is given.
The nuclear symmetry energy, which describes the energy difference of per proton and neutron in nuclear matter, has been extensively studied within the last two decades. Around saturation density, both the value and the slope of the nuclear symmetry energy have been roughly constrained, its high-density behavior is now still in argument. Probing high-density symmetry energy at terrestrial laboratories is being carried out at facilities that offer radioactive beams worldwide. While relevant experiments are being conducted, we theoretically developed more advanced isospin-dependent transport mod…
Isotope production cross sections from 112Sn + 112Sn and 124Sn + 124Sn reactions at 1 GeV/nucleon, which were measured recently at GSI using the heavy-ion accelerator SIS18 and the Fragment Separator (FRS), have been analyzed with the latest Los Alamos Monte-Carlo transport code MCNP6 using the LAQGSM03.03 event generator. MCNP6 reproduces reasonably well all the measured cross sections. Comparison of the MCNP6 results with the measured data and with calculations by a modification of the Los Alamos version of the Quark-Gluon String Model allowing for multifragmentation processes in the framewo…
We have studied the fragment yields emitted from the fragmentation of excited projectile nuclei in peripheral collisions of 136Xe+Pb at 1 GeV/nucleon, and measured with the high-resolution magnetic spectrometer, the Fragment Separator (FRS) of GSI. The mass, charge and isotope distributions of nuclear fragments formed in the reactions were calculated within a statistical ensemble approach and compared to the experimental data. The ensemble of excited projectilelike source nuclei were created in the framework of a previous analysis of similar reactions performed at 600 MeV/nucleon (ALADIN-exper…
A partial-wave analysis of NN elastic scattering data has been completed. This analysis covers an expanded energy range, from threshold to a laboratory kinetic energy of 2.5 GeV, in order to include recent elastic pp scattering data from the EDDA collaboration. The results of both single-energy and energy-dependent analyses are described.
Background: Until now the knowledge about nucleon resonances with a mass higher than 2 GeV has been scarce. Huge amounts of experimental data of the multipion photoproduction have been accumulated, and more can be expected in the future in facilities such as JLab 12 GeV. It makes it possible to investigate the decay of a nucleon resonance into another nucleon resonance. Purpose: The possibility to research the decay of the $N(2120)$ to nucleon resonances near 1.7 GeV in the three-pion photoproduction will be explored to provide useful information for future experimental study. Method: The pion…
Including O(m_c) terms in the coefficient functions and/or O(m_D) twist 3 contributions in the heavy meson distribution amplitudes leads to a non-zero transverse amplitude for exclusive neutrino production of a D pseudoscalar charmed meson on an unpolarized target. We work in the framework of the collinear QCD approach where chiral-odd transversity generalized parton distributions (GPDs) factorize from perturbatively calculable coefficient functions.
A partial-wave analysis (PWA) of NN elastic scattering data has been completed. This analysis covers an expanded energy range, from threshold to a laboratory kinetic energy of 3 GeV, in order to include recent elastic pp polarized scattering measurements performed at SATURNE II. Results of the energy-dependent fit are compared with single-energy solutions and Saclay amplitudes obtained via the direct-reconstruction approach. We also comment on the status of Eps1 in the low-energy region.
We describe a new way to access the chiral odd transversity parton distribution in the proton through the photoproduction of lepton pairs. The basic ingredient is the interference of the usual Bethe Heitler or Drell-Yan amplitudes with the amplitude of a process, where the photon couples to quarks through its chiral-odd distribution amplitude, which is normalized to the magnetic susceptibility of the QCD vacuum. A promising phenomenology of single and double spin observables emerges from the unusual features of this amplitude.
A partial-wave analysis of NN elastic scattering data has been completed. This analysis covers an expanded energy range, from threshold to a laboratory kinetic energy of 2.5 GeV, in order to include recent elastic pp scattering data produced by the EDDA collaboration at COSY. The results of both single-energy and energy-dependent analyses are described.
A parameterization of the nucleon-nucleon elastic scattering amplitude is needed for future experiments with nucleon and nuclear beams in the beam momentum range of 2 -- 50 GeV/c/nucleon. There are many parameterizations of the amplitude at $P_{lab} >$ 25--50 GeV/c, and at $P_{lab} \leq$ 5 GeV/c. Our paper is aimed to cover the range between 5 -- 50 GeV/c. The amplitude is used in Glauber calculations of various cross sections and Monte Carlo simulations of nucleon-nucleon scatterings. Usually, the differential nucleon-nucleon elastic scattering cross sections are described by an exponential e…
A calculation of the deuteron polarization observables $A^d_y$, $A_{yy}$, $A_{xx}$, $A_{xz}$ and the differential cross-section for elastic nucleon-deuteron scattering at incident deuteron energies 270 and 880 MeV in lab is presented. A comparison of the calculations with two different deuteron wave-functions derived from the Bonn-CD $NN$-potential model and the dressed bag quark model is carried out. A model-independent approach, based on an optical potential framework, is used in which a nucleon-nucleon $T$-matrix is assumed to be local and taken on the energy shell, but still depends on the…
A new resonance structure at M = 355 \pm 6 \pm 9 MeV is observed in the invariant mass spectrum of two gamma-quanta produced in the reaction d + C => gamma + gamma + x at momentum 2.75 GeV/c per nucleon. Preliminary estimates of its width and cross section are Gamma = 41 \pm 12 MeV and sigma_{gamma-gamma} = 0.6 mkb. The collected statistics is 2680 \pm 310 events of 1.5 10^6 triggered interactions of a total number 3 10^{12} dC-interactions.
This paper presents reaction cross section predictions. These predictions are the result of a continuous pipeline which originates from a microscopic nuclear interaction. Density parameters and effective nucleon-nucleon cross sections (both involved in the reaction calculations) are by-products of the same equation of state. First, we perform tests of sensitivity to medium effects using reactions involving 208-Pb, a stable but weakly isospin-asymmetric nucleus. We also show predictions for collisions of some neutron-rich isotopes of Calcium and Argon. We observe significant sensitivity of the …
With an effective Lagrangian approach, we analyze several NN \to NNππchannels by including various resonances with mass up to 1.72 GeV. For the channels with the pion pair of isospin zero, we confirm the dominance of N*(1440)\to Nσin the near threshold region. At higher energies and for channels with the final pion pair of isospin one, we find large contributions from N*(1440)\to Δπ, double-Delta, Δ(1600) \to N*(1440)π, Δ(1600) \to Δπand Δ(1620) \to Δπ. There are also sizeable contributions from Δ\to Δπ, Δ\to Nπ, N \to Δπand nucleon pole at energies close to the threshold. We well reproduce th…
The transverse mass spectra of light mesons produced in Au-Au collisions at 200 GeV/nucleon are analyzed in Tsallis statistics. In high energy collisions, it has been found that the spectra follow a generalized scaling law. We applied Tsallis statistics to the description of different particles using the scaling properties. The calculated results are in agreement with experimental data of PHENIX Collaboration. And, the temperature of emission sources is extracted consistently.
Within the framework of ImQMD05, we study several isospin sensitive observables, such as DR(n/p) ratios, isospin transport ratio (isospin diffusion), yield ratios for LCPs between the projectile region and mid-rapidity region for the reaction systems Ni+Ni, Zn+Zn, Sn+Sn at low-intermediate energies. Our results show that those observables are sensitive to the density dependence of symmetry energy, and also depend on the cluster formation mechanism. By comparing these calculations to the data, the information of the symmetry energy and reaction mechanism is obtained.
The probability of a projectile nucleon to traverse a target nucleus without interaction is calculated for central Si-Cu and Si-Pb collisions. Special attention is given to the impact parameter range which contributes to events with large transverse energy. A fit to the data from E814 requires an effective NN cross section of sigma_eff=54.2+-5.0mb (compared to the free space value sigma_in=30mb) and is interpreted as one related to wounded target nucleons.
Several nucleon-nucleon potentials, Paris, Nijmegen, Argonne, and those derived by quantum inversion, which describe the NN interaction for T-lab below 300$ MeV are extended in their range of application as NN optical models. Extensions are made in r-space using complex separable potentials definable with a wide range of form factor options including those of boundary condition models. We use the latest phase shift analyses SP00 (FA00, WI00) of Arndt et al. from 300 MeV to 3 GeV to determine these extensions. The imaginary parts of the optical model interactions account for loss of flux into d…
Antiproton production in Ni+Ni collisions at 1.85 GeV/nucleon is studied in the relativistic Vlasov-Uehling-Uhlenbeck model. The self-energies of the antiproton are determined from the nucleon self-energies by the G-parity transformation. Also, the final-state interactions of the antiproton including both rescattering and annihilation are explicitly treated. With a soft nuclear equation of state, the calculated antiproton momentum spectrum is in good agreement with recent experimental data from the heavy-ion synchrotron at GSI. The effect due to the reduced nucleon and antinucleon masses in a …
The amplitudes for the pion-nucleon charge exchange reaction of the Karlsruhe-Helsinki and the George-Washington-University partial wave analyses are compared with those of a Regge-cut model with the aim to explore the possibility to provide high energy constraints for theoretical baryon resonance analyses in the energy region above 2 GeV.
We fit the single-particle $p_t$ spectra of identified pions, kaons, and (anti)protons from central collisions of gold or lead nuclei at energies between 7.7 and 2760~GeV per nucleon pair. Blast wave model with included resonance production and with an assumption of partial chemical equilibrium is used and the fits are performed with the help of a Gaussian emulator process. A kinetic freeze-out temperature is found about 100~MeV for the lowest collision energies and 80~MeV at the LHC. The average transverse expansion velocity grows with increasing $\sqrt{s_{NN}}$ from 0.45 to 0.65. Due to part…
The probability of a projectile nucleon to traverse a target nucleus without interaction is calculated for central Si-Pb collisions and compared to the data of E814. The calculations are performed in two independent ways, via Glauber theory and using the transport code UrQMD. For central collisions Glauber predictions are about 30 to 50% higher than experiment, while the output of UrQMD does not show the experimental peak of beam rapidity particles.
The nonrelativistic full-folding optical model approach for nucleon-nucleus scattering is extended into the relativistic regime. In doing so, kinematical issues involving the off-shell Lorentz boost of the colliding particles between the two nucleons and the projectile-nucleus center-of-mass reference frames have been taken into account. The two-body effective interaction is obtained in the framework of the nuclear matter g-matrix using nucleon-nucleon optical model potentials that fully account for the inelasticities and isobar resonances in the continuum at nucleon energies up to 3 GeV. Dive…
The molecular dynamics study of fragmentation in peripheral $^{197}$Au +$^{197}$Au collisions at 35 MeV/nucleon is presented to probe the nuclear matter compressibility in low density regime. The yields of different fragment species, rapidity spectra, and multiplicities of charged particles with charge $3\leq Z \leq 80$ are analyzed at different peripheral geometries employing a soft and a hard equations of state. Fragment productions is found to be quite insensitive towards the choice of nucleon-nucleon cross sections allowing us to constrain nuclear matter compressibility. Comparison of calc…
Nuclear stopping in the heavy ion collisions over a beam energy range from SIS, AGS up to SPS is studied in the framework of the modified UrQMD transport model, in which mean field potentials of both formed and "pre-formed" hadrons (from string fragmentation) and medium modified nucleon-nucleon elastic cross sections are considered. It is found that the nuclear stopping is influenced by both the stiffness of the equation of state and the medium modifications of nucleon-nucleon cross sections at SIS energies. At the high SPS energies, the two-bump structure is shown in the experimental rapidity…
