Jet Shapes of Isolated Photon-Tagged Jets in Pb-Pb and $pp$ Collisions at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$

The modification of jet shapes in Pb-Pb collisions, relative to those in $pp$ collisions, is studied for jets associated with an isolated photon. The data were collected with the CMS detector at the LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Jet shapes are constructed from charged particles with track transverse momenta ($p_T$) above $1\mathrm{GeV}/c$ in annuli around the axes of jets with $p_T^{\text{jet}}>30\mathrm{GeV}/c$ associated with an isolated photon with $p_T^{\gamma }>60\mathrm{GeV}/c$. The jet shape distributions are consistent between peripheral Pb-Pb and $pp$ collisions, but are modified for more central Pb-Pb collisions. In these central Pb-Pb events, a larger fraction of the jet momentum is observed at larger distances from the jet axis compared to $pp$, reflecting the interaction between the partonic medium created in heavy ion collisions and the traversing partons.

Figure 1

Upper: The differential jet shape $\rho (r)$ for jets associated with an isolated photon for (from left to right) 50%–100%, 30%–50%, 10%–30%, 0%–10% Pb-Pb (solid circles), $pp$ (open circles) collisions, and from pythia simulation (histogram). Lower: The ratios of the Pb-Pb and $pp$ distributions. For the $pp$ results, the ratio is to the pythia distribution. The vertical lines through the points represent statistical uncertainties, while the shaded colored boxes indicate the total systematic uncertainties in data.