Nuclear modification factor of isolated prompt photons in pp and PbPb collisions at s NN = 5.02 TeV with the CMS detector

High-transverse-momentum prompt photons, as colorless objects, do not interact strongly with the medium and provide a direct way to test perturbative QCD and the nuclear parton distribution functions (nPDFs). The transverse energy spectra and the nuclear modification factors of isolated photons are measured in pp and PbPb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\text{TeV}$ using the CMS detector. The data are compared to jetphox next-to-leading-order calculations and found to be consistent with the prediction of the nuclear modification factor. The measurements significantly improved the accuracy compared to the previous CMS results at $\sqrt{s_{\mathrm{NN}}}=2.76\text{TeV}$. No significant modification of isolated photon cross-sections in PbPb collisions with respect to pp collisions is observed in the pseudorapidity range |η| < 1.44 for E^γ_T between 25 and 200 GeV at various collision centrality intervals.