The production of isolated photons in PbPb and pp collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV

The CMS collaboration
JHEP 07 (2020) 116, 2020.

The transverse energy ($E_\mathrm{T}^{\gamma}$) 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 $\mu$b$^{-1}$ for pp and PbPb data, respectively. The results are presented for photons with 25 $<$ $E_\mathrm{T}^{\gamma}$ $<$ 200 GeV in the pseudorapidity range $|\eta|$ $<$ 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 3

    Data from Figure 3


    Isolated photon spectra measured as a function of $E_{T}^{\gamma}$ for 0–10%, 10–30%, 30– 50%, 50–100%, and 0–100% PbPb collisions (scaled...

  • Figure 4

    Data from Figure 4


    Isolated photon cross section measured as a function of $E_{T}^{\gamma}$ in pp collisions at 5.02TeV.

  • Figure 5

    Data from Figure 5


    Nuclear modification factors $R_{AA}$ as a function of $E_{T}^{\gamma}$ measured in the 0–10%, 10–30%, 30–50%, and 50–100% centrality ranges in...

  • Figure 6

    Data from Figure 6


    Nuclear modification factors $R_{AA}$ as a function of $E_{T}^{\gamma}$ measured in the 0–100% centrality ranges in PbPb.

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