Search for the jet-induced diffusion wake in the quark-gluon plasma via measurements of jet-track correlations in photon-jet events in Pb+Pb collisions at $\sqrt{{\mathrm{s}}_{\mathrm{N}\mathrm{N}}}$ = 5.02 TeV with the ATLAS detector

This paper presents a measurement of jet-track correlations in photon-jet events, using 1.72 nb${}^{-1}$ of Pb+Pb data at $\sqrt{s_{\text{NN}}}$ = 5.02 TeV recorded with the ATLAS detector at the LHC. Events with energetic photon-jet pairs are selected, where the photon and jet are approximately back-to-back in azimuth. The angular correlation between jets and charged-particle tracks with transverse momentum ($p_{\text{T}}$) in the range 0.5-2.0 GeV in the hemisphere opposite to the jet, $\mathrm{\mid }\mathrm{\Delta }\phi \text{(jet,track)}\mathrm{\mid }>\pi \mathrm{/}2$, is measured as a function of their relative pseudorapidity difference, $\mathrm{\mid }\mathrm{\Delta }\eta \text{(jet,track)}\mathrm{\mid }$. In central Pb+Pb collisions, these correlations are predicted to be sensitive to the diffusion wake in the quark-gluon plasma resulting from the lost energy of high-$p_{\text{T}}$ partons traversing the plasma, with a characteristic modification as a function of $\mathrm{\mid }\mathrm{\Delta }\eta \text{(jet,track)}\mathrm{\mid }$. The correlations are examined with different selections on the jet-to-photon $p_{\text{T}}$ ratio to select events with different degrees of energy loss. No diffusion wake signal is observed within the current sensitivity and upper limits at 95% confidence level on the diffusion wake amplitude are reported.