Direct Photons at the CERN ISR
A hard scatter between constituent partons in hadronic interactions usually results in a system of two jets at large angles accompanied by two spectator jets. The resulting high multiplicity and the variety of contributing diagrams make the comparison with theory difficult. However, processes where one of the out-going jets is replaced by a photon often offer a more incisive comparison between experiment and theory. Photons can be produced as a result of quark-gluon collisions (Compton process) or by quark-antiquark annihilation. There are several higher order processes involving the radiation of photons from interacting quarks (bremsstrahlung process) where the photon will be close to an accompanying jet. In proton-proton collisions at ISR energies, direct photon production is predicted to be dominated by the Compton process. This implies that the recoil (away-side) jet will be a quark jet and study of the recoil jet will thus be a study of quark fragmentation. Further, it would be expected that there will be no accompanying (same-side) jet, and a measurement of the direct photon cross section will measure the gluon structure function in the interacting protons (modulo soft gluon corrections).
KeywordsTransverse Momentum Electron Pair Direct Photon Monte Carlo Program Neutral Meson
Unable to display preview. Download preview PDF.
- R.B. Nickerson, D. Phil Dissertation, 1982 (Oxford University), unpublished. C.W. Salgado, Ph.D. Dissertation (Michigan State University), in preparation. See also, A.L.S. Angelis et. al., Nucl. Phys. B244 (1984), 1.Google Scholar
- 2.W.R. Nelson, The EGS 4 Code System, SLAC Report -265 (1985). Low Energy Electron Transport with EGS, D.W.O. Rogers, Nuclear Instruments and Methods 227, 535 ( 1984 ). For details of the Monte Carlo simulation see the Ph.D. thesis of C.W. Salgado (Michigan State University).Google Scholar
- 4.E. Anassontzis, Z. Phys. C13 277 (1982).Google Scholar
- 5.T. Akesson, paper contributed to the Proceedings of the International Europhysics Conference on High Energy Physics, Bari, Italy (July 1985), p. 819.Google Scholar
- 6.P. Aurenche, Phys. Lett. 140B,, 87 (1984). See also R. Baier, “The Quark Structure of Matter”, World Scientific Publ. Co., p 113 (1986). The curves of Fig. 4 are taken from the talk of R. Baier at the XVII International Symposium on Multiparticle Dynamics, Seewinkel, Austria, ( June 1986 ).Google Scholar