Multiplicity dependence of charm baryon and meson production in pPb collisions at 8.16 TeV

Measurements of charm baryon, $\Lambda_{\rm c}^{+}$, and meson, $\mathrm{D}^0$, production yields in proton-lead collisions at a nucleon-nucleon center-of-mass energy of 8.16 TeV are presented over a wide range of event charged track multiplicities. The data were collected in 2016 with the CMS experiment with an integrated luminosity of $186\;\mathrm{nb}^{-1}$. The $\Lambda_{\rm c}^{+}$ baryon is reconstructed from the decay channel $\Lambda_{\mathrm{c}}^{+} \rightarrow \mathrm{K}_{\mathrm{S}}^{0}\;\mathrm{p}$ while $\mathrm{D}^{0}$ meson is reconstructed via $\mathrm{D}^{0}\rightarrow \mathrm{K}^-\;\pi^+$. The $\Lambda_{\rm c}^{+}$ baryon and $\mathrm{D}^{0}$ meson yields are extracted in several event multiplicity classes, up to the highest multiplicity of about 250 where long-range collective azimuthal correlations are observed for charm mesons. The production ratio of $\Lambda_{\rm c}^{+}$ to $\mathrm{D}^{0}$ is studied to explore the charm hadronization mechanism possibly in presence of a dense medium produced in high-multiplicity pPb collisions. Within uncertainties, the $\Lambda_{\rm c}^{+}$-to-$\mathrm{D}^{0}$ yield ratio is found to be consistent between the highest and the lowest multiplicities investigated, unlike the previously observed ratio of $\Lambda$/$\overline{\Lambda}$-to-${\mathrm{K}}_{\mathrm{S}}^{0}$ in pPb collisions which shows a strong multiplicity dependence. Moreover, the $\Lambda_{\mathrm{c}}^{+}$-to-$\mathrm{D}^{0}$ yield ratio is smaller than the $\Lambda$/$\overline{\Lambda}$-to-${\mathrm{K}}_{\mathrm{S}}^{0}$ one. The observation reported may indicate different event multiplicity evolution of hadronization mechanism for charm quarks than light flavor strange quarks, and provides new constraints to understand heavy flavor production and collectivity in high-multiplicity small-system collisions.