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The transverse energy (ETγ) spectra of photons isolated from other particles are measured using proton-proton (pp) and lead-lead (PbPb) collisions at the LHC at sNN = 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 < 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. [Figure not available: see fulltext.]
Sirunyan, A. M., Tumasyan, A., Adam, W., Ambrogi, F., Bergauer, T., Dragicevic, M., … Trembath-reichert, S. (2020). The production of isolated photons in PbPb and pp collisions at √sNN = 5.02 TeV. Journal of High Energy Physics, 2020(7). https://doi.org/10.1007/JHEP07(2020)116