Production of QED pairs at small impact parameter in relativistic heavy ion collisions

Hencken, Kai; Baur, G.; Trautmann, D.

doi:10.1103/physrevc.69.054902

Cited by 37 publications

(38 citation statements)

References 30 publications

(50 reference statements)

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“…As will be discussed in the next section, the mutual Coulomb excitations were required to trigger on these events, and also had the effect of selecting events with b < 30 fm, where non-perturbative effects were strongest. The cross section, pair mass, rapidity and pair p T distributions were all in accord with the predictions of lowest order perturbation theory [136]. The pair p T distribution deviated from the Weiszaecker-Williams virtual photon prediction, showing that the photon mass was important in that kinematic regime.…”

Section: Using Equation 27supporting

confidence: 70%

Physics of Ultra-Peripheral Nuclear Collisions

Bertulani

Klein

Nystrand

2005

Annu. Rev. Nucl. Part. Sci.

464

380

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Moving highly-charged ions carry strong electromagnetic fields that act as a field of photons. In collisions at large impact parameters, hadronic interactions are not possible, and the ions interact through photon-ion and photon-photon collisions known as ultra-peripheral collisions (UPC). Hadron colliders like the Relativistic Heavy Ion Collider (RHIC), the Tevatron and the LargeHadron Collider (LHC) produce photonuclear and two-photon interactions at luminosities and energies beyond that accessible elsewhere; the LHC will reach a γp energy ten times that of the Hadron-Electron Ring Accelerator (HERA). Reactions as diverse as the production of antihydrogen, photoproduction of the ρ 0 , transmutation of lead into bismuth and excitation of collective nuclear resonances have already been studied. At the LHC, UPCs can study many types of 'new physics.'

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Section: Using Equation 27supporting

confidence: 70%

Physics of Ultra-Peripheral Nuclear Collisions

Bertulani

Klein

Nystrand

2005

Annu. Rev. Nucl. Part. Sci.

464

380

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“…The same expression for the pair production amplitude, derived in the ultrarelativistic limit, is the basis for both impact parameter independent [7] and dependent [2] cross section expressions. The impact parameter independent calculation of the untagged cross section in an approximate STAR acceptance range carried out by Hencken, Baur, and Trautmann [8], 0.322 b, was reproduced with a modified version of my impact parameter independent program [7], and with a version of the code LPAIR [9,10], both to one percent accuracy.…”

mentioning

confidence: 99%

“…Test calculations with an alternative form factor that has been utilized in the literature [17] for analytical simplicity, the dipole form with Λ = 83 MeV/c, gave results in agreement with those making use of the analytical WoodsSaxon form to one percent. The lowest order QED calculation (1.9 mb) used by STAR for comparison with data (1.6 mb) mentioned above made use of an approximate analytical treatment of the Coulomb dissociation [8] combined with lowest order QED for the pair production. An alternate lowest order calculation (2.1 mb) presented by the STAR authors made use of the realistic Coulomb dissociation phenomenology [11,12,14] observed in the ZDC triggers such as adopted in the calculations here but with an equivalent photon QED calculation of the e + e − pairs.…”

mentioning

confidence: 99%

Evidence for Higher Order QED Effects ine+e−Pair Production at the BNL Relativistic Heavy Ion Collider

Baltz

2008

Phys. Rev. Lett.

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A new lowest order QED calculation for RHIC e + e − pair production has been carried out with a phenomenological treatment of the Coulomb dissociation of the heavy ion nuclei observed in the STAR ZDC triggers. The lowest order QED result for the experimental acceptance is nearly two standard deviations larger than the STAR data. A corresponding higher order QED calculation is consistent with the data. PACS: 25.75.-q, 34.90.+q In a recent publication data were presented by the RHIC STAR collaboration on "Production of e + e − pairs accompanied by nuclear dissociation in ultraperipheral heavy-ion collisions" [1]. In this publication the authors compared the experimental cross section σ with a lowest order QED calculation σ QED and concluded that "At a 90% confidence level, higher-order corrections to the cross section, ∆σ = σ − σ QED must be within the range −0.5σ QED < ∆σ < 0.2σ QED ".In this Letter, I will present a new lowest order QED cross section calculation result significantly larger than that presented in the STAR publication. This new lowest order QED cross section is now two standard deviations above the STAR experimental result. Furthermore, I find that a higher order QED calculation gives good agreement with the experimental result.The STAR experimental cross sections are for a final state with an e + e − pair in combination with mutual nuclear excitation of both ions by the ions' Coulomb fields observed in the Zero Degree Calorimeters (ZDC). Thus impact parameter dependent probabilities have to be calculated both for e + e − pair production and for mutual Coulomb dissociation of the ions.The calculations presented here make use of the method of calculating the impact parameter dependent probability of producing e + e − pairs previously described [2]. Use of an appropriate gauge allowed the electromagnetic fields of colliding ions to be represented as colliding delta functions in the ultrarelativisitic limit. The solution of the time-dependent Dirac equation for lepton pair production was thereby obtained in closed form. This solution contains higher order QED effects and goes to the known perturbative (lowest order) result in that limit. It is well known that photoproduction of e + e − pairs on a heavy target shows a negative (Coulomb) correction proportional to Z 2 that is well described by the Bethe-Maximon theory [3]. The calculated higher order heavy ion pair production cross sections show analogous reductions from perturbation theory.The impact parameter (b) dependent amplitude presents a particular numerical challenge since it involves the a rapidly oscillating phase exp(ik · b) in the integral over the transverse momentum k transfered from the ion to the lepton pair. The usual method of evaluating the perturbative impact parameter dependent probability is to first square the amplitude and then integrate over the sum and difference of k and k ′ . Here I have integrated before squaring, and I deal with the rapid oscillations with the piecewise analytical integration method previously describe...

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“…In this type of collisions, purely electromagnetic interactions and photo-nuclear interactions are the dominant processes [4,5] . Production of free e + e − pairs and bound-free production of e + e − pairs play important roles at RHIC and at LHC.…”

Section: Introductionmentioning

confidence: 99%

Lepton pair production accompanied by giant dipole resonance

Güçlü

2008

Nuclear Physics B - Proceedings Supplements

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Production of QED pairs at small impact parameter in relativistic heavy ion collisions

Cited by 37 publications

References 30 publications

Physics of Ultra-Peripheral Nuclear Collisions

Physics of Ultra-Peripheral Nuclear Collisions

Evidence for Higher Order QED Effects ine+e−Pair Production at the BNL Relativistic Heavy Ion Collider

Lepton pair production accompanied by giant dipole resonance

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