Deuteron production in AuAu collisions at $\sqrt{s_{NN}}=7–200$ GeV via pion catalysis

We study deuteron production using no-coalescence hydrodynamic $+$ transport simulations of central AuAu collisions at $\sqrt{s_{NN}}=7–200$ GeV. Deuterons are sampled thermally at the transition from hydrodynamics to transport and interact in transport dominantly via $\pi pn\leftrightarrow \pi d$ reactions. The measured proton, lambda, and deuteron transverse momentum spectra and yields are reproduced well for all collision energies considered. We further provide a possible explanation for the measured minimum in the energy dependence of the coalescence parameter $B_2\left(\sqrt{s_{NN}}\right)$ as well as for the difference between $B_2\left(d\right)$ for deuterons and that for antideuterons, $B_2\left(\overline{d}\right)$.

Figure 1

Event-averaged rates of reactions forming and disintegrating deuterons in central AuAu collisions at 7.7 GeV. For $\pi d\leftrightarrow \pi pn$ (left panel) and $Nd\leftrightarrow Npn$ (middle panel), the forward and backward rates differ by 5%–10% at most between 10 to 40 $\mathrm{fm}/c$. These reactions are close to being equilibrated. In contrast, $\pi d\leftrightarrow pn$ (right panel) has a much lower rate, it is not equilibrated, and destroys more deuterons than produces. However, the latter reaction contributes negligibly to the deuteron yield because of its low rate.

Figure 2

Proton, (anti-)deuteron, and $\mathrm{\Lambda }$ yields at midrapidity in 0%–10% central AuAu collisions from music $+$ smash simulation compared with data (proton: E895 [51], E802 [52, 53], NA49 [44, 46], PHENIX [49], STAR [43, 48]; $\mathrm{\Lambda }$: E891 [56], NA49 [57], NA57 [58], STAR [55, 59, 60]; deuteron: HADES [54], E895 [61], E802 [52], NA49 [62], STAR [63]). In panel (a) proton yield data corrected for weak decays are shown with open blue symbols, while weak-decay-inclusive data are marked with full red symbols.

Figure 3

The deuteron yield as a function of time for 0%–10% central AuAu collisions at 7.7 GeV. Two cases are compared: deuterons are sampled at particlization (red lines) and deuterons are not sampled (blue lines). Also, the effect of test-particle number is shown: $N_{\mathrm{test}}=1$ (solid lines), $N_{\mathrm{test}}=10$ (dashed lines), and $N_{\mathrm{test}}=100$ (dotted lines). The experimentally measured yields by STAR [43] and NA49 [44] are shown for comparison.

Figure 4

(a) Proton and (b) deuteron transverse momentum spectra and (c) $\langle p_T\rangle$ in 0%–10% central AuAu collisions at $\sqrt{s_{NN}}=7.7$–200 GeV from our simulation are compared with data [43, 63]. Dashed lines correspond to the hydrodynamics $+$ transport simulation, stars are experimental data points. Dotted lines in panel (b) are deuteron spectra at particlization. The difference between dashed and dotted lines demonstrates the effect of the afterburner for deuterons.

Figure 5

Comparison of the measured (a) weak-decay-corrected $B_2\left(\sqrt{s}\right)$ at $p_T/A=0.65\mathrm{GeV}$, (b) weak-decay-inclusive $B_2$, and (c) deuteron-to-proton ratio to our simulations. We tend to describe weak-decay-inclusive observables well, in contrast with poorly described weak-decay-corrected observables.

Figure 6

Revision of weak decay corrections. (a) STAR weak decay corrections (red stars) are extracted in two ways from the available publications, from $d/p$ ratio [65] and from $B_2$ [63]. It is compared with the weak decay corrections in our model (dashed line) and the thermal model (solid line). Dotted line is our approximate parametrization of STAR weak decay correction according to Eq. (11). (b) Demonstration of how the measured $\frac{N_t{N}_p}{N_d^2}$ yield ratio would change if weak decay corrections resulting from our model were adopted.