Cluster formation near midrapidity: How the production mechanisms can be identified experimentally

The formation of weakly bound clusters in the hot and dense environment at midrapidity is one of the surprising phenomena observed experimentally in heavy-ion collisions from a low center of mass energy of a few GeV up to an ultrarelativistic energy of several TeV. Three approaches have been advanced to describe the cluster formation: coalescence at kinetic freeze-out, cluster formation during the entire heavy-ion collision by potential interaction between nucleons, and deuteron production by hadronic kinetic reactions. Based on the parton-hadron-quantum molecular dynamics microscopic transport approach, which incorporates all three mechanisms for deuteron production, we identify experimental observables, which can discriminate these production mechanisms for deuterons.

Figure 1

Multiplicity of deuterons in central collisions at midrapidity, $\left|y\right|<0.5$ in PHQMD simulations for $\mathrm{Au}+\mathrm{Au}$ at ${\sqrt{s}}_{NN}=3.0$ GeV (top), for $\mathrm{Pb}+\mathrm{Pb}$ at ${\sqrt{s}}_{NN}=8.8$ GeV (middle), and for $\mathrm{Au}+\mathrm{Au}$ at ${\sqrt{s}}_{NN}=200$ GeV (bottom). The solid lines are the results of MST, the solid lines with filled squares show the bound clusters, ($E_B<0$) analyzed with aMST, whose difference to MST is explained in Ref. [12].

Figure 2

Rapidity distribution of deuterons in central collisions at a center-of-mass energy of ${\sqrt{s}}_{NN}=3$ GeV (top), ${\sqrt{s}}_{NN}=8.8$ GeV (middle), and ${\sqrt{s}}_{NN}=200$ GeV (bottom). The orange dashed lines show the results of the aMST with $E_B<0$ for ‘potential’ deuterons, the dash-dotted red lines that for coalescence deuterons and the dotted purple lines that for ‘kinetic’ deuterons produced by collisions. The solid blue lines are for the sum of the aMST and kinetic deuterons. The green dash triple-dot lines indicate the rapidity distribution of those ‘potential’ deuterons, identified by the aMST, which are at the same time ‘coalescence’ deuterons without applying the factor 3/8.

Figure 3

Same as Fig. 2 for deuterons with $p_T>1.2\mathrm{GeV}/c$.

Figure 4

Transverse momentum distribution of deuterons produced by different scenarios at midrapidity ($\left|y\right|<0.2$). The color coding is the same as in Fig 2.

Figure 5

The rapidity distribution of deuterons for the 10% most central $\mathrm{Au}+\mathrm{Au}$ collisions at $E_{\mathrm{Lab}}=11A\mathrm{GeV}$ ($\sqrt{s}=4.9$ GeV) measured by the E864 Collaboration in the interval $0.2\le p_T\le 0.4\mathrm{GeV}/c$ [20] and for 7% most central $\mathrm{Pb}+\mathrm{Pb}$ collisions from the NA49 Collaboration [21] for $E_{\mathrm{Lab}}=20$ and $40A$ GeV in comparison to the PHQMD calculations for the different scenarios. The color coding is the same as in Fig. 2.

Figure 6

The transverse momentum distributions of deuterons for the 10% most central $\mathrm{Au}+\mathrm{Au}$ collisions at $E_{\mathrm{Lab}}=11A\mathrm{GeV}$ ($\sqrt{s}=4.9$ GeV) in the rapidity interval $0\le y\le 0.2$ from the E864 Collaboration [20] and for 7% most central $\mathrm{Pb}+\mathrm{Pb}$ collisions from the NA49 Collaboration [21] for $E_{\mathrm{Lab}}=20$ and 40 $A$ GeV in the rapidity interval $-0.4\le y\le 0$ in comparison to the PHQMD calculations for the different scenarios. The color coding is the same as in Fig. 2.