We study open charm hadrons production in pp and Au+Au collisions at $\sqrt{ s_{ \mathrm{ NN}}} = 200$~GeV using an improved a multi-phase transport (AMPT) model. Specifically, we show the transverse-momentum spectra and nuclear modification factors $R_{ \mathrm{ AA}}$ of $D^{ 0}$ mesons and $\Lambda_{ c}^{ +}$ baryons, as well as the $\Lambda_{ c}^{ +}/D^{ 0}$ ratio in pp and Au+Au collisions. The results obtained from the AMPT model simulations are compared with the STAR experimental data and found to be consistent. We further investigate the $\Lambda_{ c}^{ +}/D^{ 0}$ ratio by evaluating contributions from coalescence, fragmentation, and the combined coalescence+fragmentation mechanisms, and we find that fragmentation alone underestimates the pronounced enhancement in Au+Au relative to pp at low and intermediate $p_{ \mathrm{ T}}$, whereas the coalescence+fragmentation mechanism reproduces the observed trend significantly better. These results indicate that coalescence plays a key role in charm baryon productions and helps constrain the relative importance of different hadronization mechanisms in the ultra-relativistic nuclear collisions.
Categories: hep-ph nucl-th