Medium-induced modification of Z-tagged charged particle yields in Pb+Pb collisions at 5.02 TeV with the ATLAS detector

The yield of charged particles opposite to a 𝑍 boson with large transverse momentum (𝑝_𝑇) is measured in 260  pb⁻¹ of 𝑝⁢𝑝 and 1.7  nb⁻¹ of Pb +Pb collision data at 5.02 TeV per nucleon pair recorded with the ATLAS detector at the Large Hadron Collider. The 𝑍 boson tag is used to select hard-scattered partons with specific kinematics, and to observe how their showers are modified as they propagate through the quark-gluon plasma created in Pb +Pb collisions. Compared with 𝑝⁢𝑝 collisions, charged-particle yields in Pb +Pb collisions show significant modifications as a function of charged-particle 𝑝_𝑇 in a way that depends on event centrality and 𝑍 boson 𝑝_𝑇. The data are compared with a variety of theoretical calculations and provide new information about the medium-induced energy loss of partons in a 𝑝_𝑇 regime difficult to measure through other channels.