Disappearance of flow in intermediate-energy nucleus-nucleus collisions

Xu, Hong Ming

doi:10.1103/physrevlett.67.2769

Cited by 67 publications

(55 citation statements)

References 37 publications

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“…The similar conclusions were obtained by measuring the fragment-fragment correlation for 4~ reactions at lower energies [10]. At about 85 MeV/nucleon where the in-plane collective flow disappears [22,33,34] the azimuthal distribution is nearly isotropic, the rotation-like behavior also vanishes and the particle emission has no preferential direction. Overall, at the higher energy, the emission of fragment is more isotropic at mid-rapidity and the overall character of the collective flow of nuclear matter has changed toward repulsive scattering.…”

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confidence: 74%

Rotation-like behavior as a function of projectile energy and target mass

Shen

Feng

et al. 1993

Z. Physik A - Hadrons and Nuclei

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Abstract. The azimuthal distributions produced in the intermediate energy 4~reactions are calculated via the nuclear transport theory. The rotational collective motion is observed from the mid-rapidity particles emission. In addition to the investigation on particle emission in the coordinate space, the momentum distributions of emitted particles as a function of azimuthal angle are also discussed. The azimuthal distributions are fitted by performing Legendre polynomial expansion to second order. By incorporating the fluctuation between the estimated and true reaction plane into our calculations, quantitative agreements with the data are obtained for 4~ reactions below 85 MeV/nucleon. It is found that the rotation-like behavior becomes stronger with the increasing of the impact parameter and weaker with the increasing of the projectile energy. For 4~ system at about 85 MeV/nucleon the rotation-like behavior almost vanishes and the mid-rapidity azimuthal distribution tends to be isotropic. For 35 MeV/nucleon 4~ reactions the rotation-like behavior becomes weaker and the out-of-plane enhancement of particle emission appears with the increasing of target mass. The possible origins of these target mass dependent azimuthal distributions at mid-rapidity are discussed. PACS: 25.70.PqA main goal of intermediate energy heavy ion collisions (HIC) is to investigate the dynamic mechanism and extract information about the nuclear equation of state (EOS). Various observables have been proposed in the past, including energetic particle productions, flow angles, in-plane collective flow, etc. Some models which attempt to calculate these observables can be found in recent review articles [1][2][3][4][5][6].In this work we examine the azimuthal distribution as a testing ground for the nuclear dynamics. Some experiments to measure such distributions for fission flagments, charged particles and neutrons have been performed at the both intermediate-I-7-14] and high-energy domain [-15-21]. At high energy, out-of-plane enhancement of particle emission at mid-rapidity has been discovered, so-called the squeeze-out effect. But up to now, it is not found for light reaction systems. At intermediate tenergy, m-plane enhancement of particle emission is dominant, and it is considered to have origins of such as in-plane collective flow and rotation-like behavior.The effect of the in-plane collective flow on the azimuthal distribution should result in peaking at +180 ~ at low rapidity (target rapidity region) and at 0 ~ at high rapidity (projectile rapidity region), and should vanish at midrapidity 9 So the azimuthal distribution at mid-rapidity is sensitive to the mechanism of particle emission 9 It was proved that there existed preferential emission with respect to the reaction plane on the side of target and projectile at mid-rapidity due to the rotation-like behavior at intermediate energy for some systems [12-14, 22, 23]. Although both the squeeze-out effect and the rotation-like behavior were discovered respectively at different energy d...

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supporting

confidence: 74%

Rotation-like behavior as a function of projectile energy and target mass

Shen

Feng

et al. 1993

Z. Physik A - Hadrons and Nuclei

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“…The so-called balance energy E bal (incident beam energy for which the sideward flow vanishes) has been found to be strongly dependent on σ nn for light systems, and more dependent on K ∞ for heavier systems [7]. For a fixed impact parameter and for a fixed incident energy, the flow parameter value strongly depends on K ∞ [2,8,9]. A dependence on the total isospin of the system has been also observed: keeping the total mass constant, higher values of E bal are extracted for the more neutron rich systems [10].…”

Section: Introductionmentioning

confidence: 99%

Measurements of sideward flow around the balance energy

Cussol¹,

Lefort²,

Péter³

et al. 2002

Phys. Rev. C

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Sideward flow values have been determined with the INDRA multidetector for Ar+Ni, Ni+Ni and Xe+Sn systems studied at GANIL in the 30 to 100 A.MeV incident energy range. The balance energies found for Ar+Ni and Ni+Ni systems are in agreement with previous experimental results and theoretical calculations. Negative sideward flow values have been measured. The possible origins of such negative values are discussed. They could result from a more important contribution of evaporated particles with respect to the contribution of promptly emitted particles at mid-rapidity. But effects induced by the methods used to reconstruct the reaction plane cannot be totally excluded. Complete tests of these methods are presented and the origins of the "auto-correlation" effect have been traced back. For heavy fragments, the observed negative flow values seem to be mainly due to the reaction plane reconstruction methods. For light charged particles, these negative values could result from the dynamics of the collisions and from the reaction plane reconstruction methods as well. These effects have to be taken into account when comparisons with theoretical calculations are done.

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“…Whereas it was shown for small impact parameters that the balance energy depends only weakly on the stiffness of the equation of state [8,9], a large sensitivity to the nucleonnucleon in-medium cross section was recognized [8,9,7]. The functional dependence of the balance energy on the system size can be approximately described by a power law:…”

Section: Introductionmentioning

confidence: 99%