Probing the QGP with heavy flavour

At CERN's LHC, ultra relativistic nuclear collisions yield uttermost conditions of density and temperature, casting constituent quarks and gluons into a strongly coupled system where they become the fundamental degrees of freedom, the Quark Gluon Plasma (QGP).

The underlying theory governing these collisions' evolution is Quantum Chromodynamics, in both its perturbative regime -- early hard scatterings leading to heavy quark production -- and non-perturbative regime -- medium thermalization and subsequent hadronization. Heavy quarks, b- and c-quarks, have been recently successfully employed as phenomenological probes of the QGP dynamics and effects, highlighting hints of strangeness enhancement due to thermal s-quark production and in-medium energy loss of traversing quarks.

Making use of the large heavy-ion data set collected over LHC Run 3, the prospect of studying exotic hadrons with the CMS detector in nuclear collisions emerges and offers a unique opportunity. The X(3872) exotic hadron, poised to become a novel probe of the post-collision medium, has properties that defy quark model classifications, featuring a mixed state ranging from a tightly bound tetraquark to a loosely bound meson molecule. This inner structure is highly sensitive to in-medium competing effects of dissociation and recombination, and this work leverages them towards delivering a twofold study shedding light on the X(3872) nature while simultaneously probing in-medium quark Brownian diffusion.

Furthermore, exploiting the reconstruction of similar final states, B mesons will allow to probe b-quark fragmentation fraction dependencies on kinematic and environment variables, thus highlighting a possible non-universal behavior. Together these new results will tell about the X(3872) composition, constrain hadronization models and further highlight non-trivial effects steaming from the QGP presence.