Measurement of $R=0.4$ jet mass in Pb+Pb and pp collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ATLAS detector

The measurement of the jet structure is sensitive to the angular and momentum correlations of the jet constituents. These correlations can be used to study modifications of jets in heavy ion collisions, where they provide complementary information to previously measured jet fragmentation functions. In this note, the mass divided by the transverse momentum of inclusive jets is measured using the ATLAS detector in lead-lead and proton-proton collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV delivered by the LHC. This quantity is measured for anti-$k_{t}$ $R = 0.4$ jets in intervals of jet transverse momentum and centrality in PbPb collisions and compared to the same measurements in proton-proton collisions at the same collision energy. The nuclear modification factor, $R_{AA}$, is evaluated. No significant dependence of $R_{AA}$ on the jet mass is observed.