First measurement of Λc+ production down to pT=0 in pp and p -Pb collisions at sNN =5.02 TeV

Abstract

The production of prompt Λc+ baryons has been measured at midrapidity in the transverse momentum interval 0<pT<1 GeV/c for the first time, in pp and p-Pb collisions at a center-of-mass energy per nucleon-nucleon collision sNN=5.02TeV. The measurement was performed in the decay channel Λc+→pKS0 by applying new decay reconstruction techniques using a Kalman-Filter vertexing algorithm and adopting a machine-learning approach for the candidate selection. The pT-integrated Λc+ production cross sections in both collision systems were determined and used along with the measured yields in Pb-Pb collisions to compute the pT-integrated nuclear modification factors RpPb and RAA of Λc+ baryons, which are compared to model calculations that consider nuclear modification of the parton distribution functions. The Λc+/D0 baryon-to-meson yield ratio is reported for pp and p-Pb collisions. Comparisons with models that include modified hadronization processes are presented, and the implications of the results on the understanding of charm hadronization in hadronic collisions are discussed. A significant (3.7σ) modification of the mean transverse momentum of Λc+ baryons is seen in p-Pb collisions with respect to pp collisions, while the pT-integrated Λc+/D0 yield ratio was found to be consistent between the two collision systems within the uncertainties.