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

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.