PRODUCTION OF LAMBDA_C BARYONS IN PROTON-PROTON AND LEAD-LEAD COLLISIONS AT 5.02 TEV WITH CMS

Due to the large masses, heavy quarks are produced early and experience the full evolution of the medium. The comparison between the nuclear modification factors of heavy flavor and light hadrons can provide insights into the expected flavor dependence of parton energy loss. The relative coalescence contribution to baryon production is expected to be more significant than that to mesons because of their larger number of constituent quarks. In particular, models involving coalescence of charm and light-flavor quarks predict a large enhancement in the Λ+c /D0 production ratio in the heavy ion collisions relative to pp collisions and also predict that this enhancement has a strong pT dependence.

This dissertation presents the production of inclusive (prompt) Λ+c baryons in proton- proton and lead-lead collisions at 5.02 TeV in 2015 (2017 and 2018) with CMS detector at the CERN LHC. These two analyses show that Λ+c baryons production is found to be suppressed in heavy ion collisions. This suppression is consistent with the suppression observed in D0 meson measurements. The Λ+c /D0 production ratios in pp collisions are consistent with a model obtained by adding color reconnection in hadronization to PYTHIA8. Also the Λ+c /D0 production ratios in pp collisions are consistent with the model that includes enhanced contribution from the decay of excited charm baryons and the model includes the effect of fragmentation and coalescence. There is a hint of an enhancement in the Λ+c /D0 production ratio in PbPb collisions in the pT range of 6–12.5 GeV/c compared to pp collisions. The Λ+c /D0 ratios in pp and PbPb collisions for pT > 12.5 GeV/c are found to be consistent with each other.