Λ$_{c}^{+}$ baryon production measurements with the ALICE detector at the LHC in pp and p–Pb collisions at $\sqrt{s}$$_{NN}$ = 5.02 TeV

This thesis presents new measurements of the production of prompt charmed baryon, Λ$_{c}^{+}$ in pp and p-Pb collisions at the energy of $\sqrt{s}$$_{NN}$ = 5.02 TeV made with the ALICE detector at the Large Hadron Collider (LHC). These measurements provide important information on how charm quarks hadronise in collisions involving protons and nuclei, and provide a vital reference for future measurements in Pb–Pb collisions.
The pT-differential cross section for the Λ$_{c}^{+}$ → pK−$\pi$$^{+}$ decay channel has been measured in the transverse momentum ranges 1 < $_{pT}$ < 12 GeV/c in pp collisions and 2 < $_{pT}$ < 24 GeV/c in p–Pb collisions at $\sqrt{s}$$_{NN}$ = 5.02 TeV. The Λ$_{c}^{+}$ candidates were reconstructed from tracking information from the Inner Tracking System and Time Projection Chamber, and from the particle identification information obtained by the Time-Of-Flight detector. The signal extraction was performed by fitting the invariant mass distributions in each $_{pT}$ interval after the number of background candidates had been reduced by the application of topological cuts and a Bayesian particle identification algorithm. Subsequently, the appropriate corrections for the reconstruction and selection efficiencies and the contribution from feed-down were applied to the measured Λ$_{c}^{+}$ yield. The measured cross sections in both pp and p-Pb collisions are shown to be underestimated by theoretical model predictions calculated with perturbative Quantum Chromodynamics.
The measured baryon-to-meson ratio Λ$_{c}^{+}$ /D$^{0}$ is found to be larger than that of previous measurements in $e$+$e$− experiments and any theoretical model predictions tuned on $e$+$e$− data. A better agreement with the new measurements is obtained with models that include an additional enhancement mechanism for charmed baryons, although greater precision is needed to discriminate between the models.
Finally the nuclear modification factor $R$$_{pPb}$, the ratio of the measured Λ$_{c}^{+}$ yield in p–Pb to the corresponding Λ$_{c}^{+}$ yield in pp collisions scaled by the number of binary nucleon-nucleon collisions, was extracted. The uncertainty on the measurement was reduced by the increased statistics and measurement of both collision systems at the same energy. The measured values were compared against those obtained from D-meson measurements and theory predictions, although greater precision is needed to determine the contribution of cold nuclear matter effects or hot-medium effects.
Future measurements of the Λ$_{c}^{+}$ baryon and other charmed baryons planned during the upcoming Run 3 data taking period of the LHC will hopefully provide further insight with the enhanced precision of the newly upgraded ALICE detector and shed light on the nature of hadronisation.