Peter Truoel's memories of Ken Crowe
I arrived in Berkeley in September 1967 with a PhD in low-energy nuclear physics and a small Swiss scholarship. The latter was provided by ETH Zurich in view of training young Swiss physicists as potential users of the planned meson factory, which provided first beams at the Swiss Institute of Nuclear Research in 1975 and still operates today at about 25 times the design intensity. Ken Crowe’s group in Berkeley and Val Telegdi’s group in Chicago were recommended by my supervisors in Zurich as possible options, in retrospect I considered myself fortunate to have chosen Berkeley.
The Lawrence Radiation Laboratory at that time was an intellectually very stimulating place, with in-house particle physics still possible at the Bevatron and the 184" Cyclotron. Though I knew next to nothing about particle physics in general and low energy pion physics in particular, I was received immediately as a full member of the group and entrusted by Ken with designing a beam line for an upcoming time-reversal violation test checking detailed balance in the reaction <math>\pi p \leftrightarrow \gamma n</math> in collaboration with UCLA. What I found most characteristic for the way Ken operated his group was the independence and freedom to develop one’s own ideas, which he allowed and supported for all his members including the non-academic staff. We knew that for a discussion of our ideas we could always rely on his advice, he seemed to always ask the right questions, and it was quite clear that his immense experience with carrying out pioneering experiments in pion and muon physics would provide guidance so that we would not go astray with our ideas. Many of the principal ideas of these early experiments in the fifties and sixties of the last century in which Ken participated are still with us today or have been recently repeated, e.g. search for lepton-flavor violation in muon-electron conversion, precise measurement of the muon-decay parameters, a bent-crystal spectrometer to investigate pionic X-rays and determine the pion mass, time-of-flight methods to determine the <math>\pi^0</math> mass, pion-pion scattering investigated through double pion production leading to the observation of a low energy isoscalar enhancement later to be known as the ABC-effect (A. Abashian, H. Booth, K. Crowe) whose origin is still being debated in theoretical circles, measurement of the neutron-neutron scattering length etc.
In my case he supported the construction of a pair spectrometer for intermediate energy photons to investigate radiative pion capture in nuclei, a process related to nuclear muon capture, electron scattering and (n,p) charge exchange reactions. This instrument, first equipped with optical and later with magnetostrictive readout spark chambers and finally with multiwire proportional chambers, served first for a series of experiments at the 184" Cyclotron, later at the Los Alamos meson factory LAMPF and was lastly modified for heavy ion physics at the Bevalac. This program was continued as a collaboration after I returned to Zurich in 1971, and profited greatly from the late Helmut Baer who joined Ken’s group after me. Characteristic for Ken’s way to support the careers of his young collaborators was also the invitation both Helmut Baer and I received from him to coauthor book chapters and review articles, a rewarding experience.
The only way one could really anger Ken was when we were invited as crew members for a sailing race on the San Francisco Bay: no matter what manoeuvres were to be carried out, we could only go wrong. Otherwise picnics in Tilden park or later on the platform which was to provide the base for Ken’s new home at the waterfront, and reunions at LaVal’s Pizza were part of the group's active social life. Needless to say that the late sixties made Berkeley, where many cultural, social and political movements were rooted and changes started, a truly exciting and inspiring place to live.
Though not especially successful scientifically, one of the most entertaining and courageous enterprises was the experiment where a liquid tritium target (58 kCi activity !) was exposed to a pion beam. The goal was to study the trineutron system. I guess only someone like Ken could overcome the administrative hurdles and convince LAMPF director Louis Rosen to allow this idea to materialize, which required extensive safety training and e.g. the evacuation of the whole site during transfer of the tritium to the target vessel.
Our LBL and LAMPF experience inspired a continuation of the program with a new spectrometer at SIN/PSI extending into the late eighties, in its last part (measurement of the <math>\Delta^{++}</math> magnetic moment) again in collaboration with Ken’s group.
I felt honoured and extremely touched when Ken flew over from California to join the small symposium and party for my retirement at the end of 2006. He seemed more fragile at that time already, but was in good spirits. This was the last encounter during our more than 40 years of collaboration and friendship; my own personal circumstances and schedule unfortunately prevented me from visiting California after that.
With a publication record extending over 62 years in such diverse areas as muon spin resonance in solid state physics and chemistry, muon catalysed fusion, pion-interferometry in high energy heavy ion interactions, pion induced electromagnetic interactions in nuclear physics, fundamental properties of pions and muons and their decays, and discovering and clarifying a major part of the meson spectrum through antiproton-annihilation experiments, the physics community has lost with Ken Crowe a role model for those few remaining who still find it intellectually stimulating and rewarding to occasionally try to transgress the boundaries of their own narrow fields. Quite a few of his former graduate students and postdocs, who had the chance to build their own groups, have benefitted from his continued encouragement and support and taken his example as a guideline for their own work.
Peter Truoel
29 Feb 2012
