How the first neutral-current experiments ended

At the beginning of the 1970s there seemed little reason to believe that strangeness-conserving neutral currents existed: theoreticians had no pressing need for them and several experiments suggested that they were suppressed if they were present at all. Indeed the two remarkable neutrino experiments that eventually led to their discovery were designed and built for very different purposes, including the search for the vector boson and the investigation of the parton model. In retrospect we know that certain gauge theories (notably the Weinberg-Salam model) predicted that neutral currents exist. But until 't Hooft and Veltman proved that such theories were renormalizable, little effort was made to test the new theories. After the proof the two experimental groups began to reorient their goals to settle an increasingly central issue of physics. Do neutral currents exist? We ask here: What kind of evidence and arguments persuaded the participants that they had before them a real effect and not an artifact of the apparatus~ What eventually convinced them that their experiment was over? An answer to these questions requires an examination of the organization of the experiments, the nature of the apparatus, and the previous work of the experimentalists. Finally, some general observations are made about the recent evolution of experimental physics.