Ratios of heavy baryons to heavy mesons in relativistic nucleus-nucleus collisions

Heavy baryon/meson ratios ${\Lambda }_c/D^0$ and ${\Lambda }_b/{\overline{B}}^0$ in relativistic heavy ion collisions are studied in the quark coalescence model. For heavy baryons, we include production from coalescence of heavy quarks with free light quarks as well as with bounded light diquarks that might exist in the strongly coupled quark-gluon plasma produced in these collisions. Including the contribution from decays of heavy hadron resonances and also that due to fragmentation of heavy quarks that are left in the system after coalescence, the resulting ${\Lambda }_c/D^0$ and ${\Lambda }_b/{\overline{B}}^0$ ratios in midrapidity ($\left|y\right|⩽0.5$) from central $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV are about a factor of five and ten, respectively, larger than those given by the thermal model, and about a factor of ten and twelve, respectively, larger than corresponding ratios in the PYTHIA model for $\mathit{pp}$ collisions. These ratios are reduced by a factor of about 1.6 if there are no diquarks in the quark-gluon plasma. The transverse momentum dependence of the heavy baryon/meson ratios is found to be sensitive to the heavy quark mass, with the ${\Lambda }_b/{\overline{B}}^0$ ratio being much flatter than the ${\Lambda }_c/D^0$ ratio. The latter peaks at the transverse momentum $p_T\simeq 0.8$ GeV but the peak shifts to $p_T\simeq 2$ GeV in the absence of diquarks.

Figure 1

Spectra of (a) ${\Lambda }_c$ and (b) $D^0$, and (c) the ratio ${\Lambda }_c/D^0$ in midrapidity ($\left|y\right|⩽0.5$) for central $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV. Solid lines are for the three-quark model and dashed lines are for the diquark model. Results from the PYTHIA model are shown by filled circles.

Figure 2

Same as Fig. 1 for (a) ${\Lambda }_b$ spectrum, (b) ${\overline{B}}^0$ spectrum, and (c) the ${\Lambda }_b/{\overline{B}}^0$ ratio.