First measurement of ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}$ production down to $p_{\mathrm{T}}=0$ in pp and p-Pb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}=5.02$ TeV

The production of prompt ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}$ baryons has been measured at midrapidity in the transverse momentum interval $0<p_{\mathrm{T}}<1$ GeV/$c$ for the first time, in pp and p-Pb collisions at a centre-of-mass energy per nucleon-nucleon collision $\sqrt{s_{\mathrm{N}\mathrm{N}}}=5.02$ TeV. The measurement was performed in the decay channel ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}\to \mathrm{p}{\mathrm{K}}_{\mathrm{S}}^0$ by applying new decay reconstruction techniques using a Kalman-Filter vertexing algorithm and adopting a machine-learning approach for the candidate selection. The $p_{\mathrm{T}}$-integrated ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}$ production cross sections in both collision systems were determined and used along with the measured yields in Pb-Pb collisions to compute the $p_{\mathrm{T}}$-integrated nuclear modification factors $R_{\mathrm{p}\mathrm{P}\mathrm{b}}$ and $R_{\mathrm{A}\mathrm{A}}$ of ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}$ baryons, which are compared to model calculations that consider nuclear modification of the parton distribution functions. The ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}\mathrm{/}{\mathrm{D}}^0$ baryon-to-meson yield ratio is reported for pp and p-Pb collisions. Comparisons with models that include modified hadronisation processes are presented, and the implications of the results on the understanding of charm hadronisation in hadronic collisions are discussed. A significant ($3.7\sigma$) modification of the mean transverse momentum of ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}$ baryons is seen in p-Pb collisions with respect to pp collisions, while the $p_{\mathrm{T}}$-integrated ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}\mathrm{/}{\mathrm{D}}^0$ yield ratio was found to be consistent between the two collision systems within the uncertainties.