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

Abstract

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 $\sqrt{s_{\mathrm{NN}}}=5.02$ 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 $R_{\mathrm{pPb}}$ and $R_{\mathrm{AA}}$ of ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}$ baryons, which are compared to model calculations that consider nuclear modification of the parton distribution functions. The ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}/{\mathrm{D}}^0$ 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 ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}/{\mathrm{D}}^0$ yield ratio was found to be consistent between the two collision systems within the uncertainties.

28 pages, 6 captioned figures, 7 tables, authors from page 23, published version, fix x-axis title in Fig. 2, figures at http://alice-publications.web.cern.ch/node/8657

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• Measurement of ${\Omega }_{\mathrm{c}}^0$ baryon production and branching-fraction ratio $\mathrm{BR}({\mathrm{\Omega }}_{\mathrm{c}}^0\to {\mathrm{\Omega }}^{-}{\mathrm{e}}^{+}{\nu }_{\mathrm{e}})/\mathrm{BR}({\mathrm{\Omega }}_{\mathrm{c}}^0\to {\mathrm{\Omega }}^{-}{\pi }^{+})$ in pp collisions at $\sqrt{s}$ = 13 TeV
• Soft QCD Physics at the LHC: highlights and opportunities
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• Measurement of the production cross section of prompt ${\Xi }_{\mathrm{c}}^0$ baryons in p$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV