The first measurement of pseudorapidity and azimuthal angle distributions relative to the momentum vector of a Z boson for low transverse momentum (p T) charged hadrons in lead-lead (PbPb) collisions is presented. By studying the hadrons produced in an event with a high- p T Z boson (40<350GeV), the analysis probes how the quark-gluon plasma (QGP) medium created in these collisions affects the parton recoiling opposite to the Z boson. Utilizing PbPb data at a nucleon-nucleon center-of-mass energy [b]sNN=5.02TeV from 2018 with an integrated luminosity of 1.67nb−1 and proton-proton (pp) data at the same energy from 2017 with 301pb−1, the distributions are examined in bins of charged-hadron p T. A significant modification of the distributions for charged hadrons in the range 1<2GeV in PbPb collisions is observed when compared to reference measurements from pp collisions. The data provide 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. When compared with theoretical predictions, the results are consistent with expectations of a hydrodynamic wake created when the QGP is depleted of energy by the parton propagating through it. Therefore, this Letter presents the first evidence of probe-induced energy depletion and the resulting response by the QGP medium.

Evidence of medium response to hard probes using correlations of Z bosons with hadrons in heavy ion collisions

Alexe, C.;Bruschini, D.;Ligabue, F.;
2026

Abstract

The first measurement of pseudorapidity and azimuthal angle distributions relative to the momentum vector of a Z boson for low transverse momentum (p T) charged hadrons in lead-lead (PbPb) collisions is presented. By studying the hadrons produced in an event with a high- p T Z boson (40<350GeV), the analysis probes how the quark-gluon plasma (QGP) medium created in these collisions affects the parton recoiling opposite to the Z boson. Utilizing PbPb data at a nucleon-nucleon center-of-mass energy [b]sNN=5.02TeV from 2018 with an integrated luminosity of 1.67nb−1 and proton-proton (pp) data at the same energy from 2017 with 301pb−1, the distributions are examined in bins of charged-hadron p T. A significant modification of the distributions for charged hadrons in the range 1<2GeV in PbPb collisions is observed when compared to reference measurements from pp collisions. The data provide 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. When compared with theoretical predictions, the results are consistent with expectations of a hydrodynamic wake created when the QGP is depleted of energy by the parton propagating through it. Therefore, this Letter presents the first evidence of probe-induced energy depletion and the resulting response by the QGP medium.
2026
Settore PHYS-01/A - Fisica sperimentale delle interazioni fondamentali e applicazioni
CMS; Heavy ions
   Advanced Multi-Variate Analysis for New Physics Searches at the LHC
   AMVA4NewPhysics
   European Commission
   Horizon 2020 Framework Programme - European Training Networks
   675440

   Search for Higgs bosons decaying to charm quarks
   HIGCC
   European Commission
   Horizon 2020 Framework Programme - European Research Council - Consolidator Grant
   724704

   Direct and indirect searches for new physics in events with top quarks using LHC proton-proton collisions at the CMS detector
   LHCTOPVLQ
   European Commission
   Horizon 2020 Framework Programme - Standard European Fellowships
   752730

   Majorana neutrino discovery strategy with CMS
   MajorNet
   European Commission
   Horizon 2020 Framework Programme - European Research Council - Starting Grant
   758316

   International Training Network for Statistics in High Energy Physics and Society
   INSIGHTS
   European Commission
   Horizon 2020 Framework Programme - European Training Networks
   765710

   The strong interaction at the frontier of knowledge: fundamental research and applications
   STRONG-2020
   European Commission
   Horizon 2020 Framework Programme - Research and Innovation action
   824093

   INnovative TRiggEr techniques for beyond the standard model PhysIcs Discovery at the LHC
   INTREPID
   European Commission
   Horizon Europe Framework Programme - European Research Council - HORIZON ERC Grants
   101115353

   Fundamental properties and time-scan of QCD matter at high densities and temperature exposed by jet substructure in heavy ion collisions with CMS experiment at the LHC
   QCDHighDensityCMS
   European Commission
   Horizon 2020 Framework Programme - European Research Council - Consolidator Grant
   101002207

   Power to the LHC data: an ASYmptotically MOdel-independent measurement of the W boson mass.
   ASYMOW
   European Commission
   H2020
   101001205

   Vector Boson Scattering Coordination and Action Network
   VBSCan
   COST Association
   COST Action (Horizon 2020)
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