Probing the Nuclear Equation of State byK+Production in Heavy-Ion Collisions

Abstract

The dependence of K+ production on the nuclear equation of state is investigated in heavy-ion collisions. An increase of the excitation function of K+ multiplicities obtained in heavy (Au+Au) over light (C+C) systems when going far below threshold which has been observed by the KaoS Collaboration strongly favors a soft equation of state. This observation holds despite the influence of an in-medium kaon potential predicted by effective chiral models which is necessary to reproduce the experimental K+ yields.

ϕ decay: A relevant source forK−production at energies available at the GSI Schwerionen-Synchrotron (SIS)?

“…From the analysis of the out-of-plane [28,29] and sideward flow [19,30], the K + -nucleon potential is deduced to be mildly repulsive, and the measured K + production yields are in agreement with the scenario of a soft nuclear equation of state (incompressibility modulus K N ≈ 200 MeV) [31,32]. The interpretation of the K − data is still undergoing systematic evaluations to pin down the value of the presumed attractive K − -nucleon potential and its momentum dependence.…”

“…Indeed, the combined analysis of K + and K − suggests that a substantial part of the observed K − mesons is due to a strangeness exchange mechanism [33]. Furthermore K + and K − exhibit distinctively different in-medium properties, both in theoretical approaches [1][2][3][4][5][6][7][8][9][10][31][32][33][34] and in experiments [11][12][13]15,18,19,22].…”

The high-density symmetry energy in heavy ion collisions

“…Strange kaons (in contrast to anti-strange kaons) have the additional advantage to interact weakly with nucleons in the final state, and thus constitute a particularly promising probe of the matter in heavy ion collisions. In fact, the ratio of positive kaons produced in collisions of heavy (Au + Au) relative to light (C + C) systems has been one of the most sensitive probes for the EOS of symmetric nuclear matter [15].…”

Soft nuclear equation-of-state from heavy-ion data and implications for compact stars

“…When applied to infinite isospin symmetric nuclear matter the latter corresponds to a soft nuclear equation of state characterized by a stiffness parameter K = 9 dp dn | n0 = 200 MeV [12]. While the KaoS measurements seem to suggest even lower values of K < ∼ 200MeV [12], it should also be noted that the isospin asymmetry of the colliding Au+Au system could result in an increase of K by ∼ 10% [14]. Despite being defined in the same way, the stiffness parameter K and the compression modulus K 0 must be clearly distinguished from each other.…”

“…The beam energy dependence of the K + multiplicity ratio from Au+Au and C+C collisions (M/A) Au+Au /(M/A) C+C at subthreshold energies of 0.8 to 1.5GeV per nucleon has been introduced as a sensitive and robust probe for the stiffness of nuclear matter [11]. To describe the experimental results, IQMD and RQMD (Isospin and Relativistic Quantum Molecular Dynamics) transport model calculations were performed [12,13], applying a Skyrme type U N with two-and three-body forces. Two parameter sets were chosen so as to reproduce two nucleon potentials with different levels of repulsion at supra-saturation densities.…”