Bremsstrahlung and photon production in thermal QCD

Aurenche, P.; Gelis, François; Zaraket, H.; Kobes, R.

doi:10.1103/physrevd.58.085003

Cited by 208 publications

(379 citation statements)

References 32 publications

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“…This was first noticed by Aurenche, Gelis, Kobes, and Zaraket [9], who were computing the next order corrections to Eq. (1), arising from the diagrams on the right of Fig.…”

Section: Computing the Photon Emission Ratementioning

confidence: 99%

Electromagnetic emission and energy loss in the QGP

Moore

2004

J. Phys. G: Nucl. Part. Phys.

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Abstract. I discuss why photon production from the Quark Gluon Plasma (QGP) presents an interesting problem, both experimentally and theoretically. I show how the photon emission rate can be computed under the simplifying assumption that the QGP fully thermalizes. The theoretical issues are very similar to those for jet energy loss; so it should be possible to treat them in a common formalism and relate the predictions of one phenomenon to those of the other.Submitted to: J. Phys. G: Nucl. Phys. Photons as a deep probeThe main goals of the RHIC experimental program are, to produce and to characterize the quark-gluon plasma (QGP). The plasma is defined as being a state of matter for which the density of partons (quarks and gluons) is so great that a description in terms of hadronic degrees of freedom is impossible, which is furthermore extensive and relatively close to equilibrium. The problem is that the QGP expands, cools, and hadronizes. Even after hadronization, hadrons continue to interact; much of the information about the initial state is therefore lost. For instance, the spectrum of hadronic final states which we observe at RHIC is well characterized by a thermal model with a temperature of only about 160 MeV, too low for a QGP but reasonable for the freezeout of a hadronic gas [1]. Therefore, the hadronic observables give only rather indirect information about the QGP phase of the collision.For this reason, it was proposed years ago to study "hard" probes, meaning particles which are produced early in the collision, deep within the QGP, and which then escape with little or no interaction, giving relatively direct information about the early stages of the QGP. Shuryak proposed photons as a promising direct probe [2], and they continue to be actively investigated [3].The advantage of photons as a probe of the QGP is that any photons produced are almost sure to escape without re-interacting, so they give direct, rather than indirect or processed, information about the early stages of the heavy ion collision. The main disadvantage is that there are several sources of photons, with the concomitant problem of determining which photons arose from which source. Namely, there are• Prompt photons, those produced by the initial collisions of the partons which constitute the heavy ions being collided;

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“…This was first noticed by Aurenche, Gelis, Kobes, and Zaraket [9], who were computing the next order corrections to Eq. (1), arising from the diagrams on the right of Fig.…”

Section: Computing the Photon Emission Ratementioning

confidence: 99%

Electromagnetic emission and energy loss in the QGP

Moore

2004

J. Phys. G: Nucl. Part. Phys.

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“…Further it was found [33] that photon productions from the reactions, gq → gqγ, qq → qqγ, qqq → qγ and gqq → gγ contribute in the same order as annihilation and compton processes do. The suppression due to multiple scattering during the emission process which was not mentioned in [30,31,33] was later discussed in Ref. [34].…”

mentioning

confidence: 99%

“…The photon emission rate from QGP due to compton (q(q)g → q(q)γ) and annihilation (qq → gγ) processes were evaluated [30,31] by using hard thermal loop (HTL) approximation [32]. Further it was found [33] that photon productions from the reactions, gq → gqγ, qq → qqγ, qqq → qγ and gqq → gγ contribute in the same order as annihilation and compton processes do. The suppression due to multiple scattering during the emission process which was not mentioned in [30,31,33] was later discussed in Ref.…”

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confidence: 99%

Electromagnetic signals from Au + Au collisions at RHIC energy, sNN=200 GeV and Pb + Pb collisions at LHC energy,
Nayak
¹
,
Sinha
²

2013
Physics Letters B
5
0
2
0
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We analyse the recently available experimental data on direct photon productions from Au+Au collisions at √ sNN =200 GeV RHIC and from Pb+Pb collisions at √ sNN =2.76 TeV LHC energies. The transverse momentum (pT ) distributions have been evaluated with the assumption of an initial quark gluon plasma phase at temperatures Ti=404 and 546 MeV with initial thermalisation times τi=0.2 and 0.1 fm/c respectively for RHIC and LHC energies. The theoretical evalutions agree reasonably well with the experimental observations. The thermal window for the LHC energy is justified through the ratio of the pT spectra of thermal photons to dileptons.PACS numbers: 25.75.Dw,24.85.+p It is by now conventional wisdom, that collisions between two nuclei at RHIC as well as LHC energies will lead to the formation of quark gluon plasma (QGP). Although the exact nature of QGPhadron phase transition is still plagued by uncertainties, but there are several evidences that QGP is formed [1][2][3][4] at RHIC energies. It has long been recognised that promising signals of QGP are photons and dileptons [5][6][7][8][9]. The very nature of electromagnetic interactions ensures that the thermometric signals (γ, µ + µ − , e + e − ) escape the QGP medium without any significant interaction, thus retaining the pristine information of QGP immediately after its formation. It has been pointed out by one of the authors and his collaborators, consistently for a long time [8][9][10][11][12][13][14], that the photons emanating from thermal medium show up in the p T window of 1.5 ≤ p T (GeV ) ≤ 3.5. It has also been pointed out [15,16] during the early days of QGP physics and now, that the ratio γ/µ + µ − eliminates some of the uncertainties associated with the input parameters used in the model.The concept of ratio has been revisited again in ref [17,18] where the sensitivities of the of the initial parameters have been studied extensively. The formation of a thermal medium is manifested by the flattering of the ratio beyond certain p T . Now that the direct photon data has come out of LHC we tend to analyse the data and test the above prediction at √ s N N =2.76 TeV. It is quite remarkable that the original theoretical prediction [15][16][17][18] turns out to be valid also at LHC energies with added advantage that the very high energy of LHC turns the invariant mass M , of dileptons less relevant compare to (say) at RHIC energies.It should also be noted that there is already a tantalising hint of QGP formation even at SPS energy [19,20]. In the following work we present our findings of this interesting phenomenon. Thus over a wide range of energies going through orders of magnitude, it is quite exciting to note that p T window for thermal photons and dileptons remains the same as predicted earlier, only the range of window increases almost upto 4 GeV or more at LHC energy.In this present work we have evaluated the direct photon productions from (i) Au+Au collisions at √ s N N =200 GeV for 0-5% centrality and (ii) Pb+Pb collisions at √ s N N =2.76 TeV for...

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“…As the electromagnetic signal of the QGP the production of the thermal photon has been investigated by calculating the Compton scattering and qq-annihilation processes in the QGP state [5][6][7][8][9]. Recent research [10] shows a very interesting result: the bremsstrahlung processes in the QGP state play an important role in the thermal photon production, it generates contribution of the same order of magnitude as Compton scattering and qq-annihilation processes based on the resummation of hard thermal loops [11]. So that the investigation of the bremsstrahlung processes will be a subject of intense theoretical interest.…”

Section: Introductionmentioning

confidence: 99%

“…The investigation in Ref. [10] focus on the bresstralung processes with one photon radiation induced by the parton-parton interaction inside QGP. In this paper We consider an external charged particle prepared at remote past goes through the plasma in thermal QED, which produces bresstralung radiation with N (≥ 1) photon radiation by colliding with charged constituent inside the plasma.…”

Section: Introductionmentioning

confidence: 99%

Bremsstrahlung radiation as a coherent state in thermal QED

Wang

Xiao

Zhang

2001

J. Phys. G: Nucl. Part. Phys.

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Based on fully finite temperature field theory we investigate the radiation probability in the bremsstrahlung process in thermal QED. It turns out that the infrared divergences resulting from the emission and absorption of the real photons are canceled by the virtual photon exchange processes at finite temperature. The full quantum calculation results for soft photons radiation coincide completely with that obtained in the semi-classical approximation. In the framework of Thermofield Dynamics it is shown that the bremsstrahlung radiation in thermal QED is a coherent state, the quasiclassical behavior of the coherent state leads to above coincidence.

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Bremsstrahlung and photon production in thermal QCD

Cited by 208 publications

References 32 publications

Electromagnetic emission and energy loss in the QGP

Electromagnetic emission and energy loss in the QGP

Electromagnetic signals from Au + Au collisions at RHIC energy, sNN=200 GeV and Pb + Pb collisions at LHC energy,
Nayak
¹
,
Sinha
²

2013
Physics Letters B
5
0
2
0
View full text Add to dashboard Cite

Bremsstrahlung radiation as a coherent state in thermal QED

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Bremsstrahlung and photon production in thermal QCD

Cited by 208 publications

References 32 publications

Electromagnetic emission and energy loss in the QGP

Electromagnetic emission and energy loss in the QGP

Electromagnetic signals from Au + Au collisions at RHIC energy, sNN=200 GeV and Pb + Pb collisions at LHC energy, Nayak1, Sinha2 2013Physics Letters B5020View full textAdd to dashboardCite

Bremsstrahlung radiation as a coherent state in thermal QED

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Electromagnetic signals from Au + Au collisions at RHIC energy, sNN=200 GeV and Pb + Pb collisions at LHC energy,
Nayak
¹
,
Sinha
²

2013
Physics Letters B
5
0
2
0
View full text Add to dashboard Cite