Non$-$prompt $\mathrm{D}^0$ production in heavy$-$ion collisions with ALICE
The Quark$-$Gluon Plasma (QGP) is a new matter state composited by deconfined quarks and gluons which exist at extremely high temperature and energy density. This formation of matter, predicted by Quantum Chromodynamics (QCD) in the Standard Model, shows great importance as a phenomenon to test QCD theories with its phase transitions, where the properties of matter can be investigated in ultra$-$relativistic heavy$-$ion collision experiments. At the Large Hadron Collider (LHC), the produced experiments data of heavy ion collisions create possibility for QGP researches, with phenomena such as jet quenching, where high transverse momentum partons undergo energy loss interacting with de$-$confined medium via elastic processes or induced gluon radiations, and collective motions, where the expansion of bulk matter exhibits different patterns such as isotropic and anisotropic components which are physically driven by pressure gradients. Heavy quarks, are powerful probes of QGP due to their shorter formation timescale, and they are to mostly go through the full evolution of the collision system in space$-$time. $\\$ In this thesis, the measurements of non$-$prompt $\mathrm{D}^{0}$ production in pp collisions at $\sqrt{s}=5.02~\mathrm{TeV}$ and in Pb$-$Pb collisions at $\sqrt{{s_\mathrm{NN}}}=5.02~\mathrm{TeV}$ with ALICE detectors are reported. The measurements of non$-$prompt $\mathrm{D}^{0}$, which are produced in beauty$-$hadron decays, can provide valuable information in beauty sector. The measurement of production in pp collisions is important to test perturbative QCD calculations, and provide a reference for Pb$-$Pb collisions. While in latter, the non$-$prompt $\mathrm{D}^{0}$ measurement can help to study the microscopic beauty$-$medium interactions. At high $p_{\mathrm{T}}$, it allows to investigate the colour charge and mass dependence of in$-$medium energy loss. At low $p_{\mathrm{T}}$, the participation of system collective expansion and diffusion process for beauty quarks can be investigated. $\\$ In pp collisions, the $p_{\mathrm{T}}−$differentialproductioncrosssectionofnon$−$prompt$D0$ismeasuredatmidrapidity($|y|<0.5$).The$D0$mesoncandidatesarereconstructedviathehadronicdecaychannel$D0→K−π+$.ThenspecificselectionsbasedonBoostedDecisionTrees(BDT),amachinelearningmodeltrainedwithpseudo$−$datafromMonteCarlosimulationsandbackgroundsampleindata,areappliedtothecandidates.TheapplicationofBDTreducesthecombinatorialbackground,andalsotoenhancethenon−−promptfractionof$D0$fromaround30$%$to90$%$insignals.Afterwards,thesignalsareextractedviatheinvariant$−$massanalysis,andthenon$−$promptfractionsareestimatedwithadata$−$drivenminimizing$−