Abstract:
The spectra measurements of charged hadrons produced in the shower of a parton originating in the same hard scattering with a leptonically decaying
Z
boson are reported in lead-lead nuclei (Pb-Pb) and proton-proton (
p
p
) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Both Pb-Pb and
p
p
data sets are recorded by the CMS experiment at the LHC and correspond to an integrated luminosity of
1.7
nb
−
1
and
320
pb
−
1
, respectively. Hadronic collision data with one reconstructed
Z
boson candidate with the transverse momentum
p
T
>
30
GeV
/
c
are analyzed. The
Z
boson constrains the initial energy and direction of the associated parton. In heavy ion events, azimuthal angular distributions of charged hadrons with respect to the direction of a
Z
boson are sensitive to modifications of the in-medium parton shower and medium response. compared to reference data from
p
p
interactions, the results for central Pb-Pb collisions indicate a modification of the angular correlations. The measurements of the fragmentation functions and
p
T
spectra of charged particles in
Z
boson events, which are sensitive to medium modifications of the parton shower longitudinal structure, are also reported. Significant modifications in central Pb-Pb events compared to the
p
p
reference data are also found for these observables.