Studies of parton-medium interactions using Z-tagged charged particles in PbPb collisions at $\sqrt{s_\mathrm{NN}}=5.02~\mathrm{TeV}$

The first measurements of Z boson-tagged charged hadron spectra are reported in PbPb collisions at $\sqrt{s_\mathrm{NN}}=5~\mathrm{TeV}$, using the PbPb collision data recorded by the CMS experiment at the LHC in 2018, corresponding to an integrated luminosity of $1.7~\mathrm{nb}^{-1}$. Hadronic collision data with at least one Z boson with transverse momentum $p_\mathrm{T} > 30~\mathrm{GeV}/c$ are analyzed. The azimuthal angle distributions with respect to the Z bosons, which are sensitive to medium recoils and modification of in-medium parton shower, are measured in PbPb collisions. The results indicate a modification of the angular correlation functions with respect to the reference measured in pp interactions at the same collision energy. The first measurements of Z-tagged fragmentation functions and charged particle $p_\mathrm{T}$ spectra are also reported. These measurements are sensitive to the modification of the longitudinal structure of the parton shower inside the medium. Significant modifications of the fragmentation functions and charged particle $p_\mathrm{T}$ spectra are observed.