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Electromagnetic measurement of the temperature of quark-gluon plasma produced in central ultrarelativistic nuclear collisions
Nuclear Theory · Submitted 24 May 2022
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We make the case that a minimal degree of modelling of quark-gluon plasma expansion provides a reasonable mapping between the slope of the photon energy spectrum and the maximum temperature of the plasma, as long as the slope is extracted at a reasonably high photon energy and thermal photons can be isolated from non-thermal sources.
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The abstract, sentence by sentence
Ultrarelativistic collisions of large nuclei produce a short-lived plasma of deconfined quarks and gluons. Of all the GeV-energy photons detected in these nuclear collisions, only a small number are emitted directly by the quark-gluon plasma. The characteristic near-exponential energy spectrum of these photons is often associated with an effective temperature whose interpretation is complicated by spacetime averaging, Doppler shifts and other factors. We show that the Doppler shift's effect on the slope of the photon spectrum is generally modest and can either increase or decrease the slope, in contrast to the commonly assumed blue-shifting of the photon spectrum. We make the case that a minimal degree of modelling of quark-gluon plasma expansion provides a reasonable mapping between the slope of the photon energy spectrum and the maximum temperature of the plasma, as long as the slope is extracted at a reasonably high photon energy and thermal photons can be isolated from non-thermal sources. Validating our approach using state-of-the-art numerical calculations of photon production, we highlight the challenges of contamination from non-thermal sources.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Ultrarelativistic collisions of large nuclei produce a short-lived plasma of deconfined quarks and gluons. | background 1.00 | 0.06 | 0.02 | asserted 1.00 |
| s1 | Of all the GeV-energy photons detected in these nuclear collisions, only a small number are emitted directly by the quark-gluon plasma. | background 0.95 | 0.24 | 0.02 | asserted 1.00 |
| s2 | The characteristic near-exponential energy spectrum of these photons is often associated with an effective temperature whose interpretation is complicated by spacetime averaging, Doppler shifts and other factors. | background 0.98 | 0.06 | 0.04 | asserted 0.61 |
| s3 | We show that the Doppler shift's effect on the slope of the photon spectrum is generally modest and can either increase or decrease the slope, in contrast to the commonly assumed blue-shifting of the photon spectrum. | result 0.97 | 0.90 | 0.20 | asserted 1.00 |
| s4 | We make the case that a minimal degree of modelling of quark-gluon plasma expansion provides a reasonable mapping between the slope of the photon energy spectrum and the maximum temperature of the plasma, as long as the slope is extracted at a reasonably high photon energy and thermal photons can be isolated from non-thermal sources. | contribution 0.45 | 0.83 | 0.77 | hedged possibility 0.56 |
| s5 | Validating our approach using state-of-the-art numerical calculations of photon production, we highlight the challenges of contamination from non-thermal sources. | method 0.36 | 0.90 | 0.06 | asserted 1.00 |
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The paper
Original abstract
Ultrarelativistic collisions of large nuclei produce a short-lived plasma of deconfined quarks and gluons. Of all the GeV-energy photons detected in these nuclear collisions, only a small number are emitted directly by the quark-gluon plasma. The characteristic near-exponential energy spectrum of these photons is often associated with an effective temperature whose interpretation is complicated by spacetime averaging, Doppler shifts and other factors. We show that the Doppler shift's effect on the slope of the photon spectrum is generally modest and can either increase or decrease the slope, in contrast to the commonly assumed blue-shifting of the photon spectrum. We make the case that a minimal degree of modelling of quark-gluon plasma expansion provides a reasonable mapping between the slope of the photon energy spectrum and the maximum temperature of the plasma, as long as the slope is extracted at a reasonably high photon energy and thermal photons can be isolated from non-thermal sources. Validating our approach using state-of-the-art numerical calculations of photon production, we highlight the challenges of contamination from non-thermal sources.
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References
How the literature uses it
8 arXiv papers cite this in 10 sentences
Papers citing it · 7 sentences without a confident label
Uses its method or tool 1 paper
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Its effective temperature is obtained from a backward continuation of the thermal cooling trajectory [ref] .
Origin and limits of intermediate-mass dilepton thermometry · Controlled fireball and emission setup · 0.80
Cites it as background 1 paper
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Many authors have extensively investigated various photon production mechanisms and observables, particularly the transverse momentum spectrum and the elliptic flow $v_2$ of photons [ref] .
Photon Production by Chiral Magnetic Effect in the Early Stage of High-Energy Nuclear Collisions · introduction · 0.99
What it cites · 99 sentences without a confident label
Uses data or values from 4 papers
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The function $C(N_f,E/T)$ can be found in Ref. [ref] .
Photon Emission from Quark-Gluon Plasma: Complete Leading Order Results · Temperature, velocity and volume profile of the plasma · 0.87
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For nuclear matter with equal density of baryons and antibaryons, the ratio of speed of sound to the speed of light varies from $≈1/7$ at a temperature $T=170$ MeV, to $1/3$ in the high-temperature limit [ref] .
Full result for the QCD equation of state with 2+1 flavors · Temperature, velocity and volume profile of the plasma · 0.91
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For nuclear matter with equal density of baryons and antibaryons, the ratio of speed of sound to the speed of light varies from $≈1/7$ at a temperature $T=170$ MeV, to $1/3$ in the high-temperature limit [ref] .
The equation of state in (2+1)-flavor QCD · Temperature, velocity and volume profile of the plasma · 0.91
Compares with 3 papers
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To validate Eq. [ref], we compare with numerical calculations of thermal photons from Ref. [ref] .
Multi-messenger heavy-ion collision physics · Temperature, velocity and volume profile of the plasma · 0.96
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We compare with RHIC's PHENIX measurements [ref] in Au-Au collisions $√(s_NN)=200$ GeV, and LHC's ALICE measurements [ref] in Pb-Pb collisions at $√(s_NN)=2760$ GeV, both for $0$–$20%$ centrality.
Direct photon production in Pb-Pb collisions at $\sqrt{s_\rm{NN}}$ = 2.76 TeV · Comparison with collider measurements · 0.97
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We compare with RHIC's PHENIX measurements [ref] in Au-Au collisions $√(s_NN)=200$ GeV, and LHC's ALICE measurements [ref] in Pb-Pb collisions at $√(s_NN)=2760$ GeV, both for $0$–$20%$ centrality.
2203.17187 · Comparison with collider measurements · 0.97
Cites as background 7 papers
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A large body of work indicates that relativistic fluid dynamics can describe many features of the spacetime evolution of quark-gluon plasma produced in nuclear collisions [ref] .
Hydrodynamic Approaches in Relativistic Heavy Ion Reactions · Introduction · 0.95
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A large body of work indicates that relativistic fluid dynamics can describe many features of the spacetime evolution of quark-gluon plasma produced in nuclear collisions [ref] .
Collective flow and viscosity in relativistic heavy-ion collisions · Introduction · 0.95
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A large body of work indicates that relativistic fluid dynamics can describe many features of the spacetime evolution of quark-gluon plasma produced in nuclear collisions [ref] .
Hydrodynamic Modeling of Heavy-Ion Collisions · Introduction · 0.95
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