Cold nuclear matter

Abstract

The behavior of nuclear matter is studied at low densities and temperatures using classical molecular dynamics with three different sets of potentials with different compressibility. Nuclear matter is found to arrange in crystalline structures around the saturation density and in non-homogeneous (i.e. pasta-like) structures at lower densities. Similar results were obtained with a simple Lennard-Jones potential. Finite size effects are analysed and the existence of the non-homogeneous structures is shown to be inherent to the use of periodic boundary conditions and the finitude of the system. For large enough systems the non-homogeneous structures are limited to one sphere, one rod or one slab per simulation cell, which are shown to be minimal surface structures under cubic periodic boundary conditions at the corresponding volume fraction. The relevance of these findings to the simulations of neutron star and supernovae matter is discussed.

Study of $ϕ$-meson production in $p$$+$Al, $p$$+$Au, $d$$+$Au, and $^3$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

“…These effects include multiple-parton scattering, nuclear absorption and modification of the initial partondistribution functions (PDFs) in nuclei. However, recent studies on elliptic and triangular flow in small systems suggest that QGP could be produced in p/d/ 3 He+Au collisions [5]. The flow measurements are well-explained by hydrodynamic model and are consistent with QGP droplet formation [6].…”

“…However, the volume and the lifetime of the produced medium may be insufficient for observing strangeness-enhancement and jet-quenching effects. The comparison with calculations suggests that the main production mechanisms of φ mesons at midrapidity may be different in p+Al versus p/d/ 3 He+Au collisions at √ s N N = 200 GeV. While thermal quark recombination seems to dominate in p/d/ 3 He+Au collisions, fragmentation seems to be the main production mechanism in p+Al collisions.…”

“…[1]) that in small collision systems (such as p+Al, p+Au, d+Au, and 3 He+Au), where energy and/or baryon density are not high enough to form a QGP, multiparticle production in the final state may occur without a QCD phase transition. The cold-nuclear-matter effects [3,4] seem to play a predominant role in small-system collisions at √ s N N = 200…”

“…FIG. 2.Examples of invariant-mass distributions for the K + K − pairs in3 He+Au collisions at √ s N N = 200 GeV, obtained with the (a) no PID, (b) one-kaon PID, and (c) two-kaons PID methods after subtraction of the combinatorial background estimated using the event-mixing technique.Plots correspond to integrated pT for 1.7 < pT < 2.2 GeV/c. Spectra are fitted to the sum of a Breit-Wigner function convolved with a Gaussian function to account for the φ signal, and a polynomial function to account for the residual background.…”

“…FIG.6. Experimental results on φ meson production in (a) p+Al, (b) p+Au, (c) d+Au[2], and (d)3 He+Au collisions at √ s N N = 200 GeV at midrapidity (|η| < 0.35) and comparisons to pythia/Angantyr[33] model predictions.…”