Thermal spectra can be produced by certain classes of emission kernels without probe thermalization, as when the differential cross section depends on angle but not on the Mandelstam variable s, providing a kernel-based criterion to distinguish genuine equilibrium from kernel artifacts.
Direct photon production in Pb-Pb collisions at $\sqrt{s_\rm{NN}}$ = 2.76 TeV
4 Pith papers cite this work, alongside 249 external citations. Polarity classification is still indexing.
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abstract
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.
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Relative-angle modes of pair correlations produce sign-changing modifications to the in-medium photon spectrum with magnitudes comparable to the factorized contribution.
Uses blast-wave fits to pi, K, and p spectra plus measured K/pi to predict low-pT eta/pi0 ratio, finding eta-decay photon uncertainty of order 10% of direct-photon signal at pT~1 GeV/c in central Pb-Pb at 2.76 TeV.
An analytic hydrodynamic model with QGP and hadronic photon sources reproduces measured non-prompt direct photon spectra in 200 GeV Au+Au collisions and extracts centrality-dependent initial temperatures.
citing papers explorer
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Thermal Spectra Without Detailed Balance
Thermal spectra can be produced by certain classes of emission kernels without probe thermalization, as when the differential cross section depends on angle but not on the Mandelstam variable s, providing a kernel-based criterion to distinguish genuine equilibrium from kernel artifacts.
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Probing Pair Correlations in QCD Matter with Photon Spectra
Relative-angle modes of pair correlations produce sign-changing modifications to the in-medium photon spectrum with magnitudes comparable to the factorized contribution.
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Constraining the Low-$p_T$ $\eta/\pi^0$ Ratio for Direct-Photon Analyses with Blast-Wave Fits to $\pi$, $K$, and $p$ Spectra
Uses blast-wave fits to pi, K, and p spectra plus measured K/pi to predict low-pT eta/pi0 ratio, finding eta-decay photon uncertainty of order 10% of direct-photon signal at pT~1 GeV/c in central Pb-Pb at 2.76 TeV.
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Thermal Radiation from an Analytic Hydrodynamic Model with Hadronic and QGP Sources in Heavy-Ion Collisions
An analytic hydrodynamic model with QGP and hadronic photon sources reproduces measured non-prompt direct photon spectra in 200 GeV Au+Au collisions and extracts centrality-dependent initial temperatures.