A Perspective on Lepton-photon Physics

WOLFGANG K. H. PANOFSKY Stanford Linear Accelerator Center Stanford University, Stanford, California 94309 ABSTRACT This paper reviews some key experiment,s of the past in which the same basic physical processes are attacked both through lepton-photon interactions and by using hadron machines as primary tools. Not surprisingly, it is conrludeh that the basic distinction between lepion-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 energv reach is concerned. but the superior claritv and coverage of phenomena not accessible to hadron colliders-makes it absolutely essential that the develbpment 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 promismg anoroach for the extension of knowledge bevond LEP and bevond the SSC. but the difficulties to reach an a I -. electron-positron energy of 15 TeV or beyond m the constituent frame look formidable. Both electron-positron and proton colliders appear to f&e 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.