Electromagnetic radiation from nuclear collisions at ultrarelativistic energies

Turbide, Simon; Gale, Charles; Frodermann, I. Evan; Heinz, Ulrich

doi:10.1103/physrevc.77.024909

Cited by 108 publications

(161 citation statements)

References 32 publications

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“…[27] that annihilation and Compton processes can also lead to the conversion of a quark or gluon jet into a photon. Perturbative estimates of this process at leading order indicate a sizable contribution to the total direct photon yield at intermediate p T between 3 and 6 GeV/c at RHIC energies [28][29][30][31]. The same was found for the production of virtual photons and lepton pairs [31,32].…”

Section: Flavor Conversions In Quark Gluon Plasmasupporting

confidence: 53%

“…[35] it was estimated that the sum of all direct photon sources leads to small and negative direct photon v 2 between 3 and 5% at intermediate p T . However, later it was noted that the result depends crucially on details of the fireball simulation and might be much closer to zero [31]. First experimental results are compatible with zero with sizable uncertainties [36,37].…”

Section: -2mentioning

confidence: 49%

“…Perturbative estimates of this process at leading order indicate a sizable contribution to the total direct photon yield at intermediate p T between 3 and 6 GeV/c at RHIC energies [28][29][30][31]. The same was found for the production of virtual photons and lepton pairs [31,32]. Measurements of single inclusive direct photon production from the PHENIX experiment [33] are not conclusive so far.…”

Section: Flavor Conversions In Quark Gluon Plasmamentioning

confidence: 94%

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Probing nuclear matter with jet conversions

Liu

Fries

2008

Phys. Rev. C

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We discuss the flavor of leading jet partons as a valuable probe of nuclear matter. We point out that the coupling of jets to nuclear matter naturally leads to an alteration of jet chemistry even at high transverse momentum p T . In particular, quantum chromodynamics (QCD) jets coupling to a chemically equilibrated quark gluon plasma in nuclear collisions will lead to hadron ratios at high transverse momentum p T that can differ significantly from their counterparts in p+p collisions. Flavor measurements could complement energy loss as a way to study interactions of hard QCD jets with nuclear matter. Roughly speaking they probe the inverse mean free path 1/λ while energy loss probes the average squared momentum transfer µ 2 /λ. We present some estimates for the rate of jet conversions in a consistent Fokker-Planck framework and their impact on future high-p T identified hadron measurements at RHIC and LHC. We also suggest some novel observables to test flavor effects.

show abstract

Section: Flavor Conversions In Quark Gluon Plasmasupporting

confidence: 53%

Section: -2mentioning

confidence: 49%

Section: Flavor Conversions In Quark Gluon Plasmamentioning

confidence: 94%

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Probing nuclear matter with jet conversions

Liu

Fries

2008

Phys. Rev. C

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“…It has been shown that the contributions from different sources of direct photons (apart from thermal) become significant in the photon p T spectrum for p T > 3 GeV/c [14]. However, the thermal radiation dominates the elliptic flow of direct photons up to a much larger p T (∼ 5 GeV/c) as the v 2 contributions from other sources are marginal in that range [14].…”

Section: Introductionmentioning

confidence: 99%

Elliptic flow of thermal photons from an event-by-event hydrodynamic model

et al. 2013

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Elliptic flow of direct photons in relativistic heavy ion collisions is believed to be dominated by contribution from thermal radiation of quark gluon plasma up to pT ∼ 5 GeV/c, although other sources start outshining the thermal contribution at already smaller values of pT in the direct photon spectrum. The elliptic flow of thermal photons from ideal hydrodynamics considering a smooth initial density distribution under-predicts the PHENIX direct photon data from 200A GeV Au+Au collisions at RHIC by a large margin in the range 1 < pT < 5 GeV/c. However, a significant enhancement of thermal photon production due to fluctuations in the initial QCD matter density distributions is expected. We show that such fluctuations result in substantially larger photon elliptic flow for pT > 2.5 GeV/c compared to a smooth initial-state-averaged density profile. The results from event-by-event hydrodynamics are found to be sensitive to the fluctuation size parameter. However, the effects of initial state fluctuations are insufficient to account for the discrepancy to the PHENIX data for direct photon elliptic flow. Furthermore, the photon v2 is reduced even more when we include the NLO pQCD prompt photon component. We also calculate the spectra and elliptic flow of thermal photons for 2.76A TeV Pb+Pb collisions at LHC and for the 0-40% centrality bin. Thermal photons from event-by-event hydrodynamics along with prompt photons from NLO pQCD calculations explain the ALICE preliminary direct photon data well in the region pT ≥ 2.5 GeV/c. Similar to RHIC, the elliptic flow results at LHC are again found to be much smaller than the ALICE preliminary v2 data.

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“…Recent phenomenological refinements [16,17] suggest that the QGP enhancement of direct γ production may be smaller than previously expected and partly cancelled by the quenching of fragmentation photons. Still, there is no calculation to date that consistently includes known nuclear matter effects, such as the Cronin effect [18,19,20], shadowing [21,22], and cold nuclear matter energy loss [23], to provide quantitative guidance for the relative strength of initial-and final-state modifications in the observed γ cross sections.…”

Section: Introductionmentioning

confidence: 99%

A systematic study of direct photon production in heavy ion collisions

Vitev

Zhang

2008

Physics Letters B

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A theoretical derivation of photon bremsstrahlung, induced by the interactions of an energetic quark in a hot and dense quark-gluon plasma, is given in the framework of the reaction operator approach. For the physically relevant case of hard jet production, followed by few in-medium interactions, we find that the Landau-Pomeranchuk-Migdal suppression of the bremsstrahlung photon intensity is much stronger than in the previously discussed limit of on-shell quarks and a large number of soft scatterings. This result is incorporated in the first systematic study of direct photon production in minimum bias d+Cu and d+Au and central Cu+Cu and Au+Au heavy ion collisions at the Relativistic Heavy Ion Collider at center of mass energies √ s = 62.4 GeV and 200 GeV. We find that the contribution of the photons created via final-state interactions is limited to 35% for 2 GeV< pT < 5 GeV and at high transverse momenta the modification of the direct photon cross section is dominated by initial-state cold nuclear matter effects.

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Electromagnetic radiation from nuclear collisions at ultrarelativistic energies

Cited by 108 publications

References 32 publications

Probing nuclear matter with jet conversions

Probing nuclear matter with jet conversions

Elliptic flow of thermal photons from an event-by-event hydrodynamic model

A systematic study of direct photon production in heavy ion collisions

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