A perspective on lepton-photon physics

This paper reviews some key experiments of the past in which the same basic physical processes are attacked both through lepton-photon interaction and by using hadron machines as primary tools. Not surprisingly, it is concluded that the basic distinction between lepton-photon physics and elementary particle physics in general is unreal but that the tools and methodology can be very different indeed. A look is then taken into the expected future evolution of particle accelerators. Existing accelerator technologies both for proton and electron colliders are approaching basic limits as the collision energy in the constituent frame is raised. At this time no clear path exists for electron-positron colliders to compete with the SSC as far as energy reach is concerned, but the superior clarity and coverage of phenomena not accessible to hadron colliders makes it absolutely essential that the development of both electron-positron and hadron colliders be pursued vigorously. It is concluded that accelerator R D effort underway is insufficient if a large hiatus in productivity in particle physics is to be avoided. Electron-positron linear colliders are the most promising approach for the extension of knowledge beyond LEP and beyond the SSC, but the difficulties to reach an electron-positron energy of 15 TeV or beyond in the constituent frame look formidable. Both electron-positron and proton colliders appear to face severe future detector limitations, the former due to electron-positron pair creation during the collision and the latter due to the enormous hadronic background event rates. 6 refs., 7 figs