CMS-PAS-HIN-21-019

CMS-PAS-HIN-21-019
First measurement of jet axis decorrelation with photon-tagged jets in pp and PbPb collisions at 5.02 TeV
CMS Collaboration
18 July 2024

Abstract: A search for medium-induced jet transverse momentum broadening is performed with isolated photon-tagged jet events in proton-proton (pp) and lead-lead (PbPb) collisions at nucleon-nucleon center-of-mass energy 5.02 TeV. The difference between jet axes as determined via energy-weight and winner-take-all clustering schemes, also known as the decorrelation of jet axes and denoted $ \Delta j $, is measured for the first time in photon-tagged jet events. This observable is sensitive to both multiple scattering and large-angle scattering effects in the quark gluon plasma. The pp and PbPb data samples were recorded with the CMS detector at the LHC and correspond to integrated luminosities of 1.69 nb$ ^{-1} $ and 302 pb$ ^{-1} $, respectively. Events are required to have a leading isolated photon with 60 $ < \mathrm{p}_{\mathrm{T}}^{\gamma} < $ 200 GeV, which is correlated with anti-$ \mathrm{k}_\mathrm{T} R = $ 0.3 jets with 30 $ < \mathrm{p_{T}^{jet}} < $ 100 GeV opposite in azimuthal angle. Event selection on colorless high-$ \mathrm{p_{T}} $ photons reduces the medium-induced survivor bias present in inclusive jet measurements of $ \Delta j $. The PbPb results are reported as a function of collision centrality and compared to pp reference data. Jets with $ \mathrm{p_{T}^{jet}} < $ 60 GeV have shapes for pp and PbPb which are consistent with each other. However, jets with $ \mathrm{p_{T}^{jet}} > $ 60 GeV in central PbPb show signs of narrowing relative to pp. The results are compared to the Jewel, Pyquen, and Hybrid theoretical models, which include different methods of energy loss.
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