Antideuteron and deuteron production in midcentral Pb+Pb collisions at 158$A$ GeV

Production of deuterons and antideuterons was studied by the NA49 experiment in the 23.5$\%$ most central Pb+Pb collisions at the top CERN Super Proton Synchroton (SPS) energy of $\sqrt{s_{{}_{NN}}}=17.3$ GeV. Invariant yields for $\overline{d}$ and $d$ were measured as a function of centrality in the center-of-mass rapidity range $-1.2<y<-0.6$. Results for $\overline{d}\left(d\right)$ together with previously published $\overline{p}\left(p\right)$ measurements are discussed in the context of the coalescence model. The coalescence parameters $B_2$ were deduced as a function of transverse momentum $p_t$ and collision centrality.

Figure 1

(a) $dE/dx$  versus $m^2$ for positively charged particles in the momentum interval $7<p<8$ GeV$/c$. The dashed ellipse illustrates the region populated by deuterons; the PID upper-limit $dE/dx$  cut is indicated by the horizontal line. (b) $m^2$ distributions for both charges around the $m_d^2$ position for momenta from 4 to 10 GeV$/c$ [$dE/dx$  PID cut for $d\left(\overline{d}\right)$ was applied]. The arrow indicates the nominal $m^2$ position for $d\left(\overline{d}\right)$.

Figure 2

Mass-squared distributions of $\overline{d}$ for rapidity $-1.2<y<-0.6$ in several transverse momentum bins: (a) $0<p_t<0.3$ GeV$/c$, (b) $0.3<p_t<0.45$ GeV$/c$, (c) $0.45<p_t<0.6$ GeV$/c$. Solid lines represent fits of a sum of a Gaussian signal and an exponential background.

Figure 3

Geometrical TOF acceptance as a function of rapidity $y$ and transverse momentum $p_t$ for $d$ at 158$A$ GeV.

Figure 4

The transverse momentum spectra of deuterons (a), antideuterons (b), protons (c), and antiprotons (d) in centrality selected Pb+Pb collisions at 158$A$ GeV. Only statistical errors are shown. The curves show exponential fits to the data using Eq. (2). Results for the 0–12.5$\%$ most central collisions are shown to scale, results for the centrality intervals 12.5–23.5$\%$ and 0–23.5$\%$ are divided by factors 10 and ${10}^2$, respectively.

Figure 5

$\overline{d}/d$ ratio as a function of $p_t$ in 0–23.5$\%$ central Pb+Pb collisions at 158$A$ GeV. The dashed line shows a fit to a constant.

Figure 6

Rapidity distributions for $\overline{d}$ (squares) and $d$ (circles) produced in the 23.5$\%$ most central Pb+Pb collisions at 158$A$ GeV. The solid symbols indicate the measured data points, the open symbols are reflected at midrapidity. The curves represent the results of different fits motivated by a coalescence approach (see text).

Figure 7

$dN/dy$ divided by the average number of wounded nucleons $\langle N_{\text{W}}\rangle$ for $\overline{d}$ and $d$ for Pb+Pb collisions at 158$A$ GeV.

Figure 8

Coalescence parameter $B_2$ for $d$ and $\overline{d}$ calculated from Eq. (3) in centrality selected Pb+Pb collisions at 158$A$ GeV. Centrality dependence is shown in (a), $p_t$ dependence in (b).

Figure 9

Coalescence parameters $B_2$ for $\overline{d}$ in central $A+A$ interactions at different collision energies.