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

Abstract

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 $\sqrt{s_{{}_{\mathrm{NN}}}}=5.02$ 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 ($R_{\mathrm{AA}}$). The jet $R_{\mathrm{AA}}$ is measured as a function of jet $p_{\mathrm{T}}$, the charged $k_t$ splitting scale ($\sqrt{d_{12}}$), and the angular separation ($\Delta R_{12}$) of two leading sub-jets. The jet $R_{\mathrm{AA}}$ gradually decreases with increasing $\sqrt{d_{12}}$, implying significantly stronger suppression of large-radius jets with larger $k_t$ splitting scale. The jet $R_{\mathrm{AA}}$ gradually decreases for $\Delta R_{12}$ in the range $0.01-0.2$ and then remains consistent with a constant for $\Delta R_{12}\gtrsim 0.2$. The observed significant dependence of jet suppression on the jet substructure will provide new insights into its role in the quenching process.

35 pages in total, author list starting page 18, 5 figures, 0 tables, published in Phys. Lett. B. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2020-06