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arXiv · 2602.18279

First measurement of jet axis decorrelation with photon-tagged jets in pp and PbPb collisions at 5.02 TeV

CMS Collaboration
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Abstract

The first measurement of the jet axis decorrelation in events with jets recoiling from an isolated photon is presented for lead-lead (PbPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The jet axis decorrelation is the angular difference ($\Delta{j}$) between two definitions of the jet axis. This quantity is expected to be sensitive to the scattering of jet constituents in the quark-gluon plasma (QGP). Events which have a leading isolated photon with transverse momentum 60 $\lt$ $p_{\mathrm{T}}^{\gamma}$ $\lt$ 200 GeV and recoiling jets with 30 $\lt$ $p_{\mathrm{T}}^{\text{jet}}$ $\lt$ 100 GeV are selected for the analysis. The PbPb result is reported as a function of collision centrality and compared to pp reference data. Jets with $p_{\mathrm{T}}^{\text{jet}}$ $\lt$ 60 GeV have consistent $\Delta{j}$ shapes for pp and PbPb collisions. However, a narrowing is observed for jets with $p_{\mathrm{T}}^{\text{jet}}$ $\gt$ 60 GeV in central PbPb collisions. The results are compared to predictions from the JEWEL, PYQUEN, and HYBRID theoretical models, which include different descriptions of parton energy loss in the QGP.

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CMS Collaboration. 2026-02-20. First measurement of jet axis decorrelation with photon-tagged jets in pp and PbPb collisions at 5.02 TeV. https://arxiv.org/abs/2602.18279

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