Abstract:
The transverse energy ( \({E}_{T}^{\gamma }\) ) spectra of photons isolated from other particles are measured using proton-proton (pp) and lead-lead (PbPb) collisions at the LHC at \(\sqrt{{s}_{\mathrm{NN}}}\) = 5.02 TeV with integrated luminosities of 27.4 pb\(^{−1}\) and 404 μb\(^{−1}\) for pp and PbPb data, respectively. The results are presented for photons with 25 < \({E}_{T}^{\gamma }\) < 200 GeV in the pseudorapidity range |η| < 1.44, and for different centrality intervals for PbPb collisions. Photon production in PbPb collisions is consistent with that in pp collisions scaled by the number of binary nucleon-nucleon collisions, demonstrating that photons do not interact with the quark-gluon plasma. Therefore, isolated photons can provide information about the initial energy of the associated parton in photon+jet measurements. The results are compared with predictions from the next-to-leading-order jetphox generator for different parton distribution functions (PDFs) and nuclear PDFs (nPDFs). The comparisons can help to constrain the nPDFs global fits.
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