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

Abstract

The yield of charged particles opposite to a $Z$ boson with large transverse momentum ($p_T$) is measured in 260 pb${}^{-1}$ of $pp$ 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 $pp$ 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.

28 pages in total, author list starting page 12, 3 figures, published in Phys. Rev. Lett. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2019-05/

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• Simultaneous Determination of Fragmentation Functions and Test on Momentum Sum Rule
• Strong constraints on jet quenching in centrality-dependent $p$+Pb collisions at 5.02 TeV from ATLAS
• Pushing forward jet substructure measurements in heavy-ion collisions
• Probing the in-medium $P_T$-broadening by $\gamma$+HF angular de-correlations
• Search for the jet-induced diffusion wake in the quark-gluon plasma via measurements of jet-track correlations in photon-jet events in Pb+Pb collisions at $\sqrt{{\mathrm{s}}_{\mathrm{NN}}}$ = 5.02 TeV with the ATLAS detector
• Giving wake to energy-energy correlators: Hydrodynamic response on the celestial sphere
• Hadron productions and jet substructures associated with $Z^0/\gamma$ in Pb+Pb collisions at the LHC
• Studying the QGP with Jets at the LHC and RHIC