Pair Production by Photons

Motz, J. W.; Olsen, Haakon A.; Koch, H.

doi:10.1103/revmodphys.41.581

Cited by 225 publications

(108 citation statements)

References 86 publications

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“…is the centre of momentum (CM) frame energy squared, β p c is the proton's velocity, and σ BH the total cross-section for which we use the Racah formula as parameterized by Maximon (1968) (see Formula 3D-0000 in Motz et al 1969). Changing variables, one obtains the angle-averaged cross-section…”

Section: Monte-carlo Simulationsmentioning

confidence: 99%

“…We then Lorentz transform the interacting particles to the proton rest frame and sample the positron's energy from the single-differential cross-section, dσ/dE + , for which we use the Bethe-Heitler formula for an unscreened point nucleus (Formula 3D-1000 in Motz et al 1969). Finally, the positron's direction is sampled from the double-differential cross-section, dσ/dE + dΩ + for which we use the Sauter-Gluckstern-Hull formula for an unscreened point nucleus (Formula 3D-2000 in Motz et al 1969), and its laboratory frame energy is obtained by a Lorentz transformation. For a range of proton energies, the simulation is repeated a large number of times to build up distributions in energy of positrons produced in BH pair production.…”

Section: Monte-carlo Simulationsmentioning

confidence: 99%

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Spectral and temporal signatures of ultrarelativistic protons in compact sources

Mastichiadis¹,

Protheroe

Kirk

2005

A&A

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Abstract. We present calculations of the spectral and temporal radiative signatures expected from ultrarelativistic protons in compact sources. The coupling between the protons and the leptonic component is assumed to occur via Bethe-Heitler pair production. This process is treated by modeling the results of Monte-Carlo simulations and incorporating them in a time-dependent kinetic equation, that we subsequently solve numerically. Thus, the present work is, in many respects, an extension of the leptonic "one-zone" models to include hadrons. Several examples of astrophysical importance are presented, such as the signature resulting from the cooling of relativistic protons on an external black-body field and that of their cooling in the presence of radiation from injected electrons. We also investigate and refine the threshold conditions for the "Pair Production/Synchrotron" feedback loop which operates when relativistic protons cool efficiently on the synchrotron radiation of the internally produced Bethe-Heitler pairs. We demonstrate that an additional component of injected electrons lowers the threshold for this instability.

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Section: Monte-carlo Simulationsmentioning

confidence: 99%

Section: Monte-carlo Simulationsmentioning

confidence: 99%

Spectral and temporal signatures of ultrarelativistic protons in compact sources

Mastichiadis¹,

Protheroe

Kirk

2005

A&A

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“…Our starting point is the high-energy DCS for arbitrary screening, which was derived by Bethe and Heitler from the Born approximation (Motz et al, 1969;Tsai, 1974). The Bethe-Heitler DCS for a photon of energy E to create an electron-positron pair, in which the electron has a kinetic energy E − = E − m e c 2 , can be expressed as (Tsai, 1974) …”

Section: Electron-positron Pair Productionmentioning

confidence: 99%

Radial Secondary Electron Dose Profiles and Biological Effects in Light-Ion Beams Based on Analytical and Monte Carlo Calculations using Distorted Wave Cross Sections

et al. 2008

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“…The differential cross section for the dominating BH process to the γp → l − l + p reaction has been studied in different contexts in the literature [18][19][20]. In this work, we will consider the cross section differential in the momentum transfer t and invariant mass of the lepton pair M 2 ll , and integrated over the lepton angles, which corresponds with detecting the recoiling proton only.…”

mentioning

confidence: 99%

“…(2), we propose in this work a new experimental avenue through a relative cross section measurement of the photoproduction of e − e + versus µ − µ + pairs on a proton target. Besides being a well studied process [18], the photo-production of a lepton pair has the advantage that one produces e − e + and µ − µ + final states with the same beam, and thus the overall normalization uncertainty drops out of their ratio. The analysis presented in this work shows that through a detection of the recoiling proton in the γp → l − l + p reaction, a measurement of the ratio of the e − e + cross section below µ − µ + threshold versus the e − e + + µ − µ + cross section sum above µ − µ + threshold with an absolute precision of around 7 × 10 −4 will allow to distinguish, at the 3σ level, between the proton R E extractions from muonic and electronic observables.…”

mentioning

confidence: 99%

Lepton Universality Test in the Photoproduction ofe−e+Versusμ−μ+Pairs on a Proton Target

Pauk

Vanderhaeghen

2015

Phys. Rev. Lett.

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In view of the significantly different proton charge radius extracted from muonic hydrogen Lamb shift measurements as compared to electronic hydrogen spectroscopy or electron scattering experiments, we study in this work the photoproduction of a lepton pair on a proton target in the limit of very small momentum transfer as a way to provide a test of the lepton universality when extracting the proton charge form factor. By detecting the recoiling proton in the γp → l − l + p reaction, we show that a measurement of a ratio of e − e + + µ − µ + over e − e + cross sections with an absolute precision of 7 × 10 −4 , would allow for a test to distinguish, at the 3σ level, between the two different proton charge radii currently extracted from muonic and electronic observables.Recent extractions of the proton charge radius R E from muonic hydrogen Lamb shift measurements [1,2] are in strong contradiction, by around 7 standard deviations, with the values obtained from energy level shifts in electronic hydrogen [3] or from electron-proton elastic scattering [4,5] :This so-called "proton radius puzzle" has triggered a large activity and is the subject of intense debate, see e.g. [6][7][8] for recent reviews, and references therein. Lepton universality requires the same radius to enter the electronic and muonic observables. If the different R E extractions cannot be explained by overlooked corrections, it would point to a violation of electron-muon universality. Several scenarios of new, beyond the Standard Model, physics have been proposed by invoking new particles which couple to muons and protons, but much weaker to electrons, see e.g. [9][10][11][12][13]. Such models would also lead to large loop corrections to the muon's anomalous magnetic moment, (g − 2) µ , which presently displays a 3σ deviation between experiment and its Standard Model prediction, see e.g. [14]. Explaining both the (g − 2) µ discrepancy and the proton radius puzzle by new particles coupling mainly to muons seems an attractive perspective. It does however require a significant fine-tuning, especially for larger values of the conjectured new particle masses [8]. To test the electronmuon universality, it has been proposed by the MUon proton Scattering Experiment (MUSE) [15] to make a simultaneous measurement of both µp and ep elastic scattering, extracting the proton charge form factor from both measurements. Besides the plans to measure µp elastic scattering, several new experiments are underway to extend ep scattering to lower momentum transfer values, down to 10 −4 GeV 2 , and to crosscheck its systematics [16,17]. All of these tests require absolute cross section measurements, with a required precision on each absolute cross section at the level of 1 % or better. In order to reach in µ scattering experiments the precision on R E comparable with e − scattering experiments, indicated in Eq. (2), we propose in this work a new experimental avenue through a relative cross section measurement of the photoproduction of e − e + versus µ − µ + pairs on a pr...

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Pair Production by Photons

Cited by 225 publications

References 86 publications

Spectral and temporal signatures of ultrarelativistic protons in compact sources

Spectral and temporal signatures of ultrarelativistic protons in compact sources

Radial Secondary Electron Dose Profiles and Biological Effects in Light-Ion Beams Based on Analytical and Monte Carlo Calculations using Distorted Wave Cross Sections

Lepton Universality Test in the Photoproduction ofe−e+Versusμ−μ+Pairs on a Proton Target

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