Probing the quark gluon plasma medium through B meson production measurements in PbPb collisions at the LHC

Relativistic heavy ion collisions allow the study of Quantum Chromodynamics at high energy density and temperature. Under such conditions, a medium of deconfined quarks and gluons is predicted to be formed, the Quark-Gluon Plasma (QGP). Heavy quarks are produced in the early stages of heavy ion collisions, experiencing the full evolution of the QGP medium. Exclusive beauty production measurements add precision to the study of parton energy loss and allow to probe its flavour dependence. An enhancement in strangeness content is expected in the probed medium. If beauty hadronisation happens through quark-recombination in the QGP, $B_s$ production is expected to be larger than $B^+$ production. This work employs data collected by the Compact Muon Solenoid, in PbPb collisions with a center-of-mass energy of 5.02 TeV, at the Large Hadron Collider. The first observation of $B_s$ in PbPb is presented, with a significance over 5 sigma. $B_s$ and $B^+$ cross sections are measured as a function of transverse momentum ($p_T$) and centrality. The ratios between the two are computed and compared to the fragmentation fraction ratio $f_s/f_u$, measured in pp collisions. Evidences of bottom hadronisation through recombination in the medium are shown for low B $p_T$ and more central collisions. Using the published $B_s$ cross sections in pp collisions, in the $p_T$ range of 15-50 GeV/c, the $B_s$ nuclear modification factor is computed. The measurements indicate an overall suppression of $B_s$ production in the QGP medium, in the probed kinematic region.