Observation of medium induced modifications of jet fragmentation in PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV using isolated-photon-tagged jets

Understand

Measurements of fragmentation functions for jets associated with an isolated photon are presented for the first time in pp and PbPb collisions.

• The analysis uses data collected with the CMS detector at the CERN LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV.
• Fragmentation functions are obtained for jets with p$_\mathrm{T}^\text{jet} >$ 30 GeV in events containing an isolated photon with p$_\mathrm{T}^\gamma>$ 60 GeV, using charged tracks with transverse momentum p$_\mathrm{T}^\text{trk} >$ 1 GeV in a cone around the jet axis.
• The association with an isolated photon constrains the initial p$_\mathrm{T}$ and azimuthal angle of the parton whose shower produced the jet.