Measurement of substructure-dependent suppression of large-radius jets with charged particles in Pb+Pb collisions with ATLAS

Measurements of jet substructure in Pb+Pb collisions provide key insights into the mechanism of jet quenching in the hot and dense QCD medium created in these collisions. This Letter presents a measurement of the suppression of large-radius jets with a radius parameter of $R=1.0$ and its dependence on the jet substructure. The measurement uses 1.72 nb${}^{-1}$ of Pb+Pb data and 255 pb${}^{-1}$ of $pp$ data, both at $\sqrt{s_{{}_{\mathrm{N}\mathrm{N}}}}=5.02$ TeV, recorded with the ATLAS detector at the Large Hadron Collider. Large-radius jets are reconstructed by reclustering $R=0.2$ calorimetric jets and are measured for transverse momentum above $200$ GeV. Jet substructure is evaluated using charged-particle tracks, and the overall level of jet suppression is quantified using the jet nuclear modification factor ($R_{\mathrm{A}\mathrm{A}}$). The jet $R_{\mathrm{A}\mathrm{A}}$ is measured as a function of jet $p_{\mathrm{T}}$, the charged $k_t$ splitting scale ($\sqrt{d_{12}}$), and the angular separation ($\mathrm{\Delta }{R}_{12}$) of two leading sub-jets. The jet $R_{\mathrm{A}\mathrm{A}}$ gradually decreases with increasing $\sqrt{d_{12}}$, implying significantly stronger suppression of large-radius jets with larger $k_t$ splitting scale. The jet $R_{\mathrm{A}\mathrm{A}}$ gradually decreases for $\mathrm{\Delta }{R}_{12}$ in the range $0.01-0.2$ and then remains consistent with a constant for $\mathrm{\Delta }{R}_{12}\gtrsim 0.2$. The observed significant dependence of jet suppression on the jet substructure will provide new insights into its role in the quenching process.