Rapidity dependence of deuteron production in central $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV

We have measured the distributions of protons and deuterons produced in the 20% most central $\mathrm{Au}+\mathrm{Au}$ collisions at the Relativistic Heavy-Ion Collider (RHIC) ($\sqrt{s_{{}_{\mathrm{NN}}}}=200$ GeV) over a very wide range of transverse and longitudinal momentum. Near midrapidity we have also measured the distribution of antiprotons and antideuterons. We present our results in the context of coalescence models. In particular, we extract the “homogeneity volume” and the average phase-space density for protons and antiprotons. Near central rapidity the coalescence parameter $B_2(p_T)$ and the space-averaged phase-space density $\langle f\rangle (p_T)$ are very similar for both protons and antiprotons. For protons we see little variation of either $B_2(p_T)$ or the space-averaged phase-space density as the rapidity increases from 0 to 3. However, these quantities depend strongly on $p_T$ at all rapidities. These results are in contrast to data from lower-energy collisions where the proton and antiproton phase-space densities are different at $y=0$, and both $B_2$ and $\langle f\rangle$ depend strongly on rapidity.

Figure 1

Ring radius versus momentum for particles at $y\approx 3$ showing the pion, kaon, proton, and deuteron separation. The bands show the proton and deuteron selection used in the analysis.

Figure 2

$p_T$-dependent feed-down correction factors for protons versus $p_T$ and rapidity. The three sets of lines show the effect of various scenarios for the difference in shape between proton and $\Lambda$ spectra. Systematic errors on the correction due to uncertainties in the yield ratio of protons and Lambdas are shown by the bands to the left of the plots. The curves for antiprotons are very similar.

Figure 3

(Anti)Proton and (anti)deuteron $p_T$ spectra at various rapidities for the top $20\%$ most central $\mathrm{Au}+\mathrm{Au}$ collisions. The filled-symbol part of the spectra show the $p_T$ intervals used in the coalescence analysis. Note that the limits for the deuteron range are exactly twice those used for the protons. The errors are statistical only. The horizontal bars represent the bin width.

Figure 4

$B_2$ versus transverse momentum per nucleon at several rapidities for central $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{{}_{\mathrm{NN}}}}=200$ GeV. Protons are displayed with filled circles and antiprotons with filled triangles. The solid line in the top-left panel is an exponential fit to the data at $y=0$. This same line is shown, in dotted form, in the other three panels. The errors are statistical only.

Figure 5

(Anti)Proton space-averaged phase-space density $\langle f\rangle (m_T/A)$ for central $\sqrt{s_{{}_{\mathrm{NN}}}}=200$ GeV $\mathrm{Au}+\mathrm{Au}$ collisions at several rapidities. The solid line in the top-left panel is an exponential fit to the data at $y=0$. This same line is shown, in dotted form, in the other three panels. The errors are statistical only.

Figure 6

Proton space-averaged phase-space density for central collisions as a function of $\sqrt{s_{{}_{\mathrm{NN}}}}$ and $m_T$ at $y=0$ [13, 23, 26, 27]. The errors are statistical only.