A Survey of $\upsilon$ _μe Physics with Emphasis on Recent Fermilab Results

Abstract

From both an experimental and an historical point of view it is particularly appropriate to summarize the development of $\upsilon$ _μe^- physics at this time. Historically, it was ten years ago last week that the announcement (see Figure 1) of the first $\upsilon$ _μe^- event was sent from Aachen to the other members of the Gargamelle Collaboration. The event, shown in Figure 2, is of a single electron identified via its characteristic bremsstrahlung and curvature. The significance of this event far exceeds its visual impact. With a background¹⁾ of less than.03 events, it became the first solid indication for the existence of the weak neutral current. On the experimental front, the investigation of the $\upsilon$ _μe interaction is about to enter a new phase, having graduated from experiments yielding 2–3 events to those which will be analyzing hundreds of events. With these high statistics experiments it should be possible to study the differential as well as the total crosssections of $\upsilon$e and $\upsilon$ _μe scattering. Before reviewing the increasingly sophisticated methods with which the experimentalists have studied $\upsilon$ _μe scattering, let’s briefly recall how the theoretical interpretation has evolved.