Several accounts have been written of the discovery of neutral weak currents, mainly by social scientists or theoreticians. Although doubtless well motivated, these authors were themselves not immersed in the experimental situation in neutrino physics in the 1960s and 1970s. There have also been, of course, nonhistorical reviews of the physics of neutral currents. In this chapter I shall present an experimenter's account of the sequence of events in this discovery, based on my own experience and on discussions with other physicists taking part in those experiments. As emphasized earlier in this volume by Leon Lederman (see Chapter 6), discoveries in high-energy physics are frequently stories of false trails, crossed wires, sloppy technique, misconceptions, and misunderstandings, compensated by the occasional incredible strokes of good luck. Certainly this was the case for neutral currents.

It is well known that neutral currents were discovered in 1973 by a collaboration operating with the bubble chamber Gargamelle at the CERN Proton Synchrotron. Gargamelle (shown in Fig. 25.1) was a large (4.8 m long, 1.9 m diameter) heavy-liquid chamber filled with freon (CF3Br) with 20 tons total mass. For the neutral-current investigation, a relatively small fiducial volume of 3 m3 (4.5 metric tons) was employed. The chamber was conceived and constructed by André Lagarrigue with the help of engineers from Saclay, and funded largely by the French atomic energy commission. Other physicists participating included André Rousset and Paul Musset, who were prominent in the subsequent physics program at CERN.