Photon Photon Collisions pp 1-44 | Cite as

# Photon-photon production in Hadron-Hadron collisions

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## Abstract

Quantum Chromodynamic (QCD) estimates are made for the large transverse momentum production of single and double photons in pp, \(\overline p p\), and π^{±}p collisions.In addition to the pure QED annihilation term \(q\overline q\) → γγ, it is found that the QCD induced gluon-gluon subprocess gg → γγ, is an important source of double photons. Photon Bremsstrahlung contributions are also examined.

## Keywords

Transverse Momentum Photon Bremsstrahlung Naive Estimate Invariant Cross Section Photon Rate
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## References

- 1.E. Berger, E. Braaten, and R. D. Field, “The Large P
_{T}Production of Single and Double Photons in Proton-Proton and Pion-Proton Collisions”, University of Florida preprint UFTP-83-10.Google Scholar - 2.There are many estimates of single photon production available in the literature. See, for example, H. Fritzsch and P. Minkowski, Phys. Lett. 69B, 316 (1977); R. Ruckl, S. Brodsky, and J. Gunion, Phys. Rev. D18, 2469 (1978); F. Halzen and D. Scott, Phys. Rev. Lett. 40, 1117 (1978); Phys. Rev. D18, 3378 (1978); R. D. Field, “Dynamics of High Energy Reactions”, plemary session talk at the XIX International Conference on High Energy Physics, Tokyo, 1978; L. Cormell and J. F. Owens, Florida State University preprint FSU-HEP-030780 (1980); R. Horgan and P. Scharbach, Nucl. Phys. B181, 421 (1981); A. P. Contogouris, S. Papadopoulos, and C. Papavassiliou, Nucl. Phys. B179, 461 (1981); F. Paige and I. Stumer, Proc. ISABELLE Summer Study, Brookhaven, 1981.Google Scholar
- 3.Direct two-photon production in hadronic interactions by the QED annihilation subprocess, \(q\overline q\)→γγ, was discussed as early as 1971 by S. Berman, J. D. Bjorken, and J. Kogut, Phys. Rev. D4, 3388 (1971).Google Scholar
- 4.R. N. Cahn and J. F. Gunion, Phys. Rev. D20, 2253 (1979).Google Scholar
- 5.The importance of the gg→γγ was first pointed out by B. L. Combridge, Nucl. Phys. B174, 243 (1980). See also, C. Carimalo, M. Crozon, P. Kessler, and J. Parisi, Phys. Lett. 98B, 105 (1981): M. Krawsgyk and W. Ochs, Phys. Lett. 79B, 119 (1978).Google Scholar
- 6.The gg→γγ and gg→γγ differential cross sections are arrived at by inserting the appropriate color factors into the γγ→γγ amplitudes calculated by B. De Tollis, Nuovo Cimento 35, 1182 (1965).Google Scholar
- 7.I have not included the effects of the parton intrinsic transverse momentum within the initial hadrons in the analysis presented here. The effect of “smearing” over the parton intrinsic transverse momentum is, however, important at low PT and in regions where the cross section is steeply falling. For example, smearing over the parton intrinsic transverse momentum can raise the W=27.4 GeV single photon rates by as much as a factor of two. On the other hand, the ratios of the double to single photon production presented in Figs. 2, 8, 11, and 14 are not affected greatly by smearing since I have not required the two photons to balance transverse momentum. The ratio simply measures the fraction of photon triggers that contain a photon on the away-side.Google Scholar
- 8.A. Nicolaidis, Nucl. Phys. 163, 156 (1980).Google Scholar
- 9.I adopt here the notation of S. D. Ellis and M. B. Kislinger, Phys. Rev. D9, 2027 (1974).Google Scholar

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© Springer-Verlag 1983