Parton-hadron-quantum-molecular dynamics: A novel microscopic n -body transport approach for heavy-ion collisions, dynamical cluster formation, and hypernuclei production

Abstract

We present the novel microscopic n-body dynamical transport approach PHQMD (Parton-Hadron-Quantum-Molecular-Dynamics) for the description of particle production and cluster formation in heavy-ion reactions at relativistic energies. The PHQMD extends the established PHSD (Parton-Hadron-String-Dynamics) transport approach by replacing the mean-field by density dependent two body interactions in a similar way as in the Quantum Molecular Dynamics (QMD) models. This allows for the calculation of the time evolution of the n-body Wigner density and therefore for a dynamical description of cluster and hypernuclei formation. The clusters are identified with the MST (Minimum Spanning Tree) or the SACA (Simulated Annealing Cluster Algorithm) algorithm which -by regrouping the nucleons in single nucleons and noninteracting clusters -generates the most bound configuration of nucleons and clusters. Collisions among particles in PHQMD are treated in the same way as in PHSD. The PHQMD approach can be used in different modes for the hadron propagation: the mean-field based PHSD mode and the QMD mode based on different density dependent two-body potentials between the nucleons which correspond to the different equationsof-state (EoS). This allows to study the sensitivity of observables on the different descriptions of the potential interactions among nucleons. Here we present the first PHQMD results for general 'bulk' observables such as rapidity distributions and transverse mass spectra for hadrons (π, K,K, p,p, Λ,Λ) from SIS to RHIC energies, as well as for cluster production, including hypernuclei.

Charged-pion production in $$\mathbf {Au+Au}$$ collisions at $$\sqrt{\mathbf {s}_{\mathbf {NN}}} = 2.4~{\mathbf {GeV}}$$

“…3). The missing yields in the tails of the rapidity distributions are estimated by using the d N/dy shape obtained from five transport models (IQMD, PHSD, GiBUU, SMASH) [15][16][17][18]20] (see Sect. 4).…”

“…In the following the data will be compared to five stateof-the-art microscopic transport models: "Isospin Quantum Molecular Dynamics" (IQMD vi.c8) [15], "Parton Hadron String Dynamics" (PHSD v4) [16], "Parton-Hadron-Quantum-Molecular Dynamics" (PHQMD v1) [20], "Simulating Many Accelerated Strongly-Interacting Hadrons" (SMASH v1.5.1) [18,19], and "Giessen Boltzmann-Uehling-Uhlenbeck" (GiBUU, release 2019) [17]. 1 We study the differences between model predictions as observed in the rapidity, transverse momentum, and polar angle distributions of charged pions, in the trends of the A 2 parameter as a function of p cm and system size, and in the predicted abundance of resonances as well.…”

“…3.3, we present the centrality and momentum dependence of the parameter A 2 which quantifies the pion production anisotropy. The presentation of our results ends with a detailed comparison of the observables discussed in the previous sections to five state-of-the-art microscopic models [15][16][17][18][19][20] in Sect. 4.…”

Astrophysics in the Laboratory—The CBM Experiment at FAIR

“…These sequential collisions happen more frequently at high densities, and, therefore, the yield of multi-strange hyperons reflect the density in the fireball. The sensitivity of multi-strange hyperon production on the density of the reaction volume, and, hence, on the EOS, has been calculated with the novel PHQMD transport mode [31]. Preliminary results indicate, that in Au-Au collisions at FAIR energies the expected yields of Ξ − and Ω − hyperons and even more of Ξ + and Ω + anti-hyperons, are substantially higher for a soft EOS than for a stiff EOS.…”

Exploring Cosmic Matter in the Laboratory—The Compressed Baryonic Matter Experiment at FAIR

“…This sensitivity is expected to increase at beam energies close to or even below the production threshold, as was the case for kaon production at beam energies around 1 A GeV at SIS18. Preliminary results of calculations with the novel Parton-Hadron-Quantum-Molecular Dynamics (PHQMD) transport model indicate that the yields of Ξ − and Ω − hyperons and even more of Ξ + and Ω + anti-hyperons produced in A+A collisions at FAIR energies depend significantly on the EOS [24]. For a soft EOS, higher densities are reached than for a stiff EOS, and, hence, the number of multiple-collisions increases, resulting in a higher yield of multi-strange hyperons.…”