Charm baryon production at central rapidity in proton-proton collisions at centre-of-mass energy of 13 TeV

Abstract

By colliding heavy-ions accelerated close to the speed of light the building blocks of ordinary matter, quarks and gluons, are not in their usual state by being confined inside hadrons. Instead they form a hot and dense medium called the Quark-Gluon Plasma. This primordial medium is of fundamental importance as it existed a few microseconds after the Big Bang. Up until now, proton-proton collisions have been used as reference for lead-lead collisions, since it was not believed that small systems could create the necessary conditions of a Quark-Gluon Plasma. However, recent experimental results in high multiplicity proton-proton collisions resemble the ones that are usually attributed to the creation of a Quark-Gluon Plasma in heavy-ion collisions. These observations led to the question whether the underlying physical origin between these experimental results is the same across all collision systems.

This project measured the transverse momentum differential corrected yield of prompt charmed lambda baryons with the ALICE detector at the Large Hadron Collider (LHC) in 1.5 billion proton-proton collisions at a centre-of-mass energy of 13 TeV at midrapidity. Charm quarks are produced from initial hard scattering processes that can be calculated by the theory of the strong interaction, Quantum Chromodynamics. Therefore, the charm quark can test calculations made with one of the three pillars of the Standard Model of Particle Physics. The charmed lambda baryon is reconstructed in the hadronic decay mode of a charmed lambda baryon decaying into a proton and K-short meson. Due to its low production rate and hard to reconstruct decay topology, a sophisticated machine learning technique has been used to extract a signal from the dominating background. This study lays grounds to perform the measurement as function of event activity, allowing to make a first step in shedding light whether a Quark-Gluon Plasma is also created in collision between two partons.