Measurement of isolated-prompt photon–hadron correlations in Pb–Pb collisions at $$\sqrt{{s}_{{\textrm{NN}}}} = 5.02$$ TeV

The ALICE Collaboration has measured the azimuthal correlation between trigger isolated-prompt photons and associated charged hadrons in Pb–Pb collisions at the CERN LHC, at a centre-of-mass energy per nucleon pair of √sNN = 5.02 TeV. The trigger isolated-prompt photons are measured in the transverse-momentum range 18 < pTγ < 40 GeV/c and pseudorapidity range |ηγ | < 0.67. The isolation selection is based on a charged particle isolation momentum threshold pT iso, ch = 1.5 GeV/c within a cone of radius R = 0.2. The associated charged particles are measured in the transverse-momentum ranges pT h > 1.8 GeV/c and pseudorapidity |ηh | < 0.9. The yield D(zT ) of associated hadrons per trigger, with zT = pT h / pT γ , is measured in three Pb–Pb collision centrality classes: central (0–30%), semicentral (30–50%), and peripheral (50–90%). The D(z T ) measurement in pp collisions with the same pT γ interval was too limited statistically, but at a lower pT γ interval, showing agreement with theoretical predictions. Therefore, an approximation to the standard IAA is computed from the D(z T) conditional yields, using NLO pQCD predictions as pp reference, the IpQCD. A strong suppression of this ratio is observed in central collisions compared to peripheral collisions. The result extends to a lower pT γ relative to those reported in previously published Pb–Pb collisions measurements at √sNN = 5.02 TeV. The I pQCD measurement is compared to IAA calculations with an NLO pQCD model that includes energy loss, and to the CoLBT-hydro model. The IpQCD results from central collisions are also compared with IAA measurements of jets correlated with isolated- prompt photons and of hadrons correlated with Z0 bosons, both reported by the CMS Collaboration at the LHC, as well as with direct photon–hadron correlation IAA measurements reported by the PHENIX and STAR Collaborations at RHIC.