Symmetry energy dependence of long-timescale isospin transport

Abstract

Isospin transport occurring within dinuclear projectile-like fragments (PLFs) produced in heavyion collisions is explored as a probe of the nuclear symmetry energy. Within the framework of the Constrained Molecular Dynamics model (CoMD), the existence of the long-lived dinuclear PLFs, for up to 800 fm/c, is observed. It is demonstrated that changes in the N/Z of the two fragments resulting from the breakup of the dinuclear PLF is due to isospin transport. The rate of the transport between the two fragments is shown to be dependent on the slope of the symmetry energy at saturation density. Comparison of the CoMD calculations with experimental data establish that the evolution of N/Z could be used to constrain the density dependence of the symmetry energy. Introduction. The nuclear Equation of State (nEoS), which describes the fundamental properties of infinite nuclear matter, has been the motivation for a broad range of experimental studies. Of particular interest is how the nEoS evolves as a function of the neutron-to-proton ratio (N/Z) of nuclear matter, which is defined by the symmetry energy term of the nEoS [1-3]. The symmetry energy, which is often discussed in reference to its density dependence, E sym (ρ), represents the difference in binding energy between pure neutron matter and symmetric nuclear matter (N = Z). Constraining the form of the density dependence of the symmetry energy is critical for understanding the properties of asymmetric nuclear matter. For example, the masses, collective excitations, and neutron skin thicknesses of finite nuclei are dependent on E sym (ρ) [2,[4][5][6][7][8][9][10][11][12][13]. Beyond the terrestrial laboratory, the symmetry energy has an essential role in the properties and evolution of neutron stars and core-collapse supernovae [14][15][16][17][18][19][20].Constraints on E sym (ρ) are often reported based on the magnitude, E sym (ρ 0 ), and the slope, L = 3ρ •

Detailed characterization of neutron-proton equilibration in dynamically deformed nuclear systems

“…Recently this idea has been revived to investigate equilibration within a deformed PLF*. For different ranges of rotation angle, a clear generally decreasing trend of the neutron-richness of the LF is observed, and a timescale is obtained [18][19][20][21]. In [22] we have reported high-resolution characterization of NZ equilibration by measuring the composition of the HF and LF with sufficiently high angular resolution to demonstrate an exponential dependence of the composition with time, indicative of first-order kinetics.…”

Shannon information entropy in heavy-ion collisions

“…A better description of the properties of hot nuclei may be achieved by CoMD than QMD. The charge distribution of intermediate-mass fragments are reasonably reproduced, except for the problems in the multi-particle multiplicities [98,99,100].…”

“…The expansion time depends on the initial conditions, such as the incident energy, and the asymmetry of the system [96,99,121,122,123,124,125]. It can be short in case of central collisions of symmetric nuclei (∼ 50 fm/c), and also long to few 100 fm/c in the case of peripheral heavy-ion collisions [126].…”

Constraints on the asymmetric equation of state from heavy-ion collisions

“…There is a clear decrease in the asymmetry of the light fragment as a function of time. [33,34] Recent analysis was performed on data from the 70 Zn+ 70 Zn reaction at 35 MeV/nucleon using the NIMROD array. Events were selected where at least two mass identified fragments were detected.…”