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Direct photon production in Pb-Pb collisions at $\sqrt{s_\rm{NN}} =$ 2.76 TeV

The collaboration
Phys.Lett. B754 (2016) 235-248, 2016

Abstract (data abstract)
CERN-LHC. Direct photon production at mid-rapidity in Pb-Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 2.76$ TeV was studied in the transverse momentum range $0.9 < p_\mathrm{T} < 14$ GeV$/c$. Photons were detected with the highly segmented electromagnetic calorimeter PHOS and via conversions in the ALICE detector material with the $e^+e^-$ pair reconstructed in the central tracking system. The results of the two methods were combined and direct photon spectra were measured for the 0-20%, 20-40%, and 40-80% centrality classes. For all three classes, agreement was found with perturbative QCD calculations for $p_\mathrm{T} \gtrsim 5$ GeV$/c$. Direct photon spectra down to $p_\mathrm{T} \approx 1$ GeV$/c$ could be extracted for the 20-40% and 0-20% centrality classes. The significance of the direct photon signal for $0.9 < p_\mathrm{T} < 2.1$ GeV$/c$ is $2.6\sigma$ for the 0-20% class. The spectrum in this $p_\mathrm{T}$ range and centrality class can be described by an exponential with an inverse slope parameter of $(297 \pm 12^\mathrm{stat}\pm 41^\mathrm{syst})$ MeV. State-of-the-art models for photon production in heavy-ion collisions agree with the data within uncertainties.

• #### Table 1

Data from Fig. 5

10.17182/hepdata.73093.v1/t1

Invariant differential yields of direct GAMMA produced in 0-20% central inelastic PbPb collisions at center-of-mass energy per nucleon 2.76 TeV.

• #### Table 2

Data from Fig. 5

10.17182/hepdata.73093.v1/t2

Invariant differential yields of direct GAMMA produced in 20-40% central inelastic PbPb collisions at center-of-mass energy per nucleon 2.76 TeV....

• #### Table 3

Data from Fig. 5

10.17182/hepdata.73093.v1/t3

Invariant differential yields of direct GAMMA produced in 40-80% central inelastic PbPb collisions at center-of-mass energy per nucleon 2.76 TeV....

• #### Table 4

Data from Fig. 4

10.17182/hepdata.73093.v1/t4

Double Ratio RGAMMA in 0-20% central inelastic PbPb collisions at center-of-mass energy per nucleon 2.76 TeV.

• #### Table 5

Data from Fig. 4

10.17182/hepdata.73093.v1/t5

Double Ratio RGAMMA in 20-40% central inelastic PbPb collisions at center-of-mass energy per nucleon 2.76 TeV.

• #### Table 6

Data from Fig. 4

10.17182/hepdata.73093.v1/t6

Double Ratio RGAMMA in 40-80% central inelastic PbPb collisions at center-of-mass energy per nucleon 2.76 TeV.

• #### Table 7

Data from not in paper

10.17182/hepdata.73093.v1/t7

Invariant differential yields of inclusive GAMMA produced in 0-20% central inelastic PbPb collisions at center-of-mass energy per nucleon 2.76 TeV.

• #### Table 8

Data from not in paper

10.17182/hepdata.73093.v1/t8

Invariant differential yields of inclusive GAMMA produced in 20-40% central inelastic PbPb collisions at center-of-mass energy per nucleon 2.76 TeV.

• #### Table 9

Data from not in paper

10.17182/hepdata.73093.v1/t9

Invariant differential yields of inclusive GAMMA produced in 40-80% central inelastic PbPb collisions at center-of-mass energy per nucleon 2.76 TeV.