Nuclear modification factor of nonphotonic electrons in heavy-ion collisions, and the heavy-flavor baryon-to-meson ratio

The nuclear modification factor $R_{\mathit{AA}}$ of nonphotonic electrons in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV is studied by considering the decays of heavy-flavor hadrons produced in a quark coalescence model. Although an enhanced ${\Lambda }_c/D^0$ ratio is predicted by the coalescence model, it is peaked at small transverse momenta ($~2$ GeV) due to the large difference between heavy and light quark masses. As a result, the enhanced ${\Lambda }_c/D^0$ ratio, which is expected to suppress the electron $R_{\mathit{AA}}$ as the branching ratio of ${\Lambda }_c$ decay into electrons is smaller than that of $D^0$, does not lead to additional suppression of the electron $R_{\mathit{AA}}$ at large transverse momenta ($⩾5$ GeV), where the suppression is mainly due to heavy quark energy loss in produced quark-gluon plasma. Also, the enhanced ${\Lambda }_b/{\overline{B}}^0$ ratio predicted by the coalescence model has even smaller effect on the nonphotonic electron $R_{\mathit{AA}}$ as bottom baryons and mesons have similar branching ratios for semileptonic decays into electrons.

Figure 1

Spectra of electrons from decays of all charmed hadrons. Shown in the inset are the ${\Lambda }_c/D^0$ ratios in fragmentation and in both the three-quark and diquark-quark coalescence models.

Figure 2

The electron $R_{\mathit{AA}}$ in the central collision of $\mathrm{Au}+\mathrm{Au}$ at $\sqrt{s_{\mathit{NN}}}=200$ GeV from charmed hadrons. The solid line is the result obtained from only fragmentation of heavy quarks with energy loss. The dot-dot-dashed (dashed) line is for the three-quark (diquark-quark) coalescence model, while the dot-dashed line is obtained with $D^0$ meson only in the diquark-quark coalescence model. The dotted line is from the toy model described in the text and the data are from Ref. [3].

Figure 3

The electron $R_{\mathit{AA}}$ in the central collision of $\mathrm{Au}+\mathrm{Au}$ at $\sqrt{s_{\mathit{NN}}}=200$ GeV from bottom hadrons. Notations are the same as in Fig. 2.