Evidence of the medium response with Z-hadron correlations in PbPb and pp collisions at sqrt(sNN) = 5.02 TeV

CMS Physics Analysis Summaries
Report number	CMS-PAS-HIN-23-006
Title	Evidence of the medium response with Z-hadron correlations in PbPb and pp collisions at sqrt(sNN) = 5.02 TeV
Corporate author(s)	CMS Collaboration
Collaboration	CMS Collaboration
Subject category	Nuclear Physics - Experiment
Accelerator/Facility, Experiment	CERN LHC ; CMS
Abstract	The first measurement of low transverse momentum ($p_\mathrm{T}$) charged hadron pseudorapidity and azimuthal angle distributions relative to $Z$ bosons in PbPb collisions at a nucleon-nucleon center-of-mass energy $\sqrt{s_\mathrm{NN}} = 5.02$ TeV is presented. This study utilizes PbPb collision data recorded in 2018 with an integrated luminosity of $1.67 \pm 0.03$ nb$^{-1}$, as well as pp collision data acquired in 2017 with an integrated luminosity of $301 \pm 6$ pb$^{-1}$. For the first time in PbPb collisions, the azimuthal angle and pseudorapidity distributions of charged hadrons relative to $Z$ bosons are measured in bins of charged hadron $p_\mathrm{T}$ to search for in-medium parton shower modifications and medium recoil effects. The analysis focuses on events containing at least one $Z$ boson with $40 < p_\mathrm{T} < 350$ GeV. A significant modification in the azimuthal angle and pseudorapidity distributions for charged hadrons in the low $p_\mathrm{T}$ range, around 1 to 2 GeV, is observed compared to reference measurements from pp collisions. The results are consistent with expectations from phenomenological models, including medium recoil and the medium response to hard probes traversing the quark-gluon plasma. The data provide significant new information about the correlation between hard and soft particles in heavy ion collisions, which can be used to test predictions of various jet quenching models. In data comparisons with models, the first evidence for medium recoil and hole effects caused by a hard probe is found.
Other source	Inspire
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