It was early 1978 and the group was very busy. In those days, it seems we were always very busy, but the winter of 1978 was especially so. A new polarized electron source had been installed on the linac, and we were commissioning it, testing a new spectrometer in the end station, and also learning how to use new beam-monitoring and beam-steering apparatus. We were preparing to look for parity violation in deeply inelastic electron scattering, an effect that was predicted by the Weinberg-Salam Model.
Willi had just finished his term as CERN director-general and came to SLAC for a sabbatical visit. We welcomed our distinguished visitor and invited him to join in the experimental activity, something that suited us and seemed to suit him as well. Willi’s first action was to purchase his first pair of blue jeans. After all, this was a necessary part of one’s wardrobe if one’s preparing to work on shift. Willi never pretended he would contribute anything technical to the experiment, and we didn’t really expect that or ask. We were happy to have someone around with his experience and perspective on the field. We did tease him, however, as being our oldest graduate student.
Willi became particularly interested in one aspect of the experiment. The spin-polarized electrons had to have their spins rapidly flipped in order to measure the small parity violating asymmetries that arise from the weak electromagnetic interference. This was done by rapidly reversing the circular polarization of the laser beam that drove the photoemission source and polarized the electrons. The heart of the experiment was a device, a Pockels cell, a commonly used optical component that, when biased by a voltage, provides a quarter wave retardation of the laser beam. Willi was fascinated by the Pockels cell, invented by Friedrich Pockels in 1893. Willi descended on our library staff for help in locating the original turn-of-the-century scientific papers (in German, of course) so he could learn about these devices. We assume he found the papers. He was always delighted to lecture anyone who would listen about the physics and history of Pockels cells.
Willi participated in the shifts through the spring 1978 runs, culminating in the observation of a parity violating signal in the electron-scattering process. He didn’t take evening or owl shifts, but was usually around during the days, particularly in the afternoons around 4 p.m. at shift change. That was the busiest time. The collaboration was small enough to meet in the counting house, and at shift change at four we would meet informally to discuss progress and plans for the next day or so. Willi enjoyed those somewhat disorganized meetings and discussions.
We released our first results in the early summer of 1978, and Willi was present for that event. Happily we were allowed to include his name on the publication. We believe he returned home later, satisfied with his experimental sojourn and his visit to SLAC. A gentleman, a great physicist, and a great friend, we will miss him.