Remembering Willy Haeberli

photo of Willy Haeberli

Several current and emeritus professors, department alumni, and colleagues sent thoughts and memories about Willy Haeberli, who passed away October 4, 2021.

If you would like to contribute your thoughts, a story, or anything in memory of Willy, please email Sarah Perdue (

View the department obituary

View the State Journal obituary

View the Willy Haeberli Memorial Symposium Website

Lee Pondrom

When I arrived in the Department in 1963 Willy had been here already for 11 years, and was a full professor. Experimental nuclear physics was a major player in Department research. Other senior faculty members included Ray Herb, Heinz Barschall, and Hugh Richards. The group had a large collection of graduate students and illustrious alumni, and was one of the leading groups in the country. Following the Manhattan Project, nuclear physics enjoyed a high national priority.

I had previously done some work in nuclear physics myself, but was hired into the High Energy Physics group, so I was a knowledgeable outside observer of the nuclear physics group.

The Sterling Hall bombing in August 1970, was a major catastrophe for nuclear physics. The van loaded with explosives was parked next to tandem accelerator laboratory, and the damage was extensive. The reconstruction of the facility and the implementation of polarized beams in the tandem was spearheaded by Willy. This led to a renaissance for the program that gave at least another 20 years of fruitful research.

Willy had a long and productive career at the University of Wisconsin. Among his many contributions to the Department, the tandem research program after the Sterling Hall bombing was outstanding.

Louis Bruch

I actually was a student in an undergraduate course (electricity and magnetism) Willy taught in 1958-59. It went well. He was a very up-beat instructor and got a good response from the students. He was supportive when I was Chair and I know of other faculty who found him supportive professionally.

Wilmer Anderson

I knew Willy Haeberli for over 60 years. He was an exceptional scientist. He was an expert in polarized nuclear ion sources and polarized nuclear targets.

During his long career at Wisconsin, he constructed the world’s finest Lamb shift, atomic beam, and colliding beam polarized ion sources. His developments in ion sources were very original. He also made pioneering measurements on the dependence of nuclear cross sections on the polarization of the incident nucleon.

In more recent years, he and Tom Weiss developed a polarized nuclear gas target. This is a very important and original development because it involved developing target walls that did not depolarize the gas. He and others have been active in the use of this target.

Willy was also very helpful in assisting others. Tom Clegg, a former postdoc with Willy and now a professor at The University of North Carolina, told me he tries to emulate Willy in his teaching of grad student and in many other ways. He trained many grad students. I personally was aided by Willy in many ways. I remember one day Willy came to my office and said he need some atomic cross sections measured for his research on ion sources. I said I was interested, but I did not have the equipment of such measurements. He immediately said he would ask his grad students to build an accelerator for me that summer if I got my students to work with them. In about two months we had an operating 20-100 keV accelerator. I used this accelerator in my research for the next 35 years.

I have heard many students compliment Willy on his teaching. He was in all respects a great physics professor. Wisconsin was very lucky to have him.

I took a lunch out to Willy’s home and ate and visited him about 2 months ago. He was weak and required oxygen, but he was still sharp mentally and very gracious. I greatly miss him.

Paul Quin

Willy Haeberli was my mentor, my colleague, and my friend. I first met Willy on a very cold and snowy 1968 winter morning and soon learned that I, a newly minted postdoc, was transient, while graduate students were legacy. Nuclear physics at Wisconsin was a top ranked program, led by Heinz Barschall, Willy, Hugh Richards and Bob Borchers, with more than forty postdocs and graduate students. Both Barschall and Haeberli were awarded the Tom Bonner Prize in Nuclear Physics and were members of the National Academy of Sciences.

Of the four Professors Willy was the most adventurous and demanding, pushing his students and postdocs to do more than what was planned and pursue the unexpected – he was often in the lab well into the night and before the crack of dawn. After a timid beginning, I convinced Willy and Heinz to join forces and combine their expertise in polarized-beam and neutron physics in the first experiments in neutron producing experiments initiated by a polarized beam.

On August 24, 1970, a truck loaded with explosives destroyed most of the nuclear physics facility in Sterling Hall and murdered Robert Fassnacht, a fellow postdoc in solid-state physics. The radiation hazards were secured shortly after the blast, enabling the first responders free access to the area. One week later, the Third International Symposium on Polarization Phenomena in Nuclear Reactions was held in Madison, recognizing the stature of the nuclear physics program led by Haeberli and Barschall. The facilities were rebuilt, and nuclear physics at Madison retained a leadership position for more than thirty years.

I joined the Department of Physics faculty in 1971, and over the years Willy and I and our students and postdocs collaborated on many experiments in Madison. Our weekly group meetings were seminars with Willy leading the way, always teaching and always encouraging others to explore alternatives. Willy and I had a symbiotic relationship: he continued innovative polarized beam and target development while I developed advanced data acquisition and computer analysis hardware and software. Together we advanced our understanding of nature and taught many others to be scientists.

Willy Haeberli encouraged his students to do better than they thought they could do, work hard and be civil to everyone. I was fortunate to spend many years as one of his students, and many years as one of his friends.

Bob Joynt

Warmth, kindness, generosity, industriousness, humor:  Willy had every human virtue that I can think of.  HIs death leaves a great void in the world.

Jay Davis

As a student of Heinz’s in the 60s, Willy was close to my heart.  We once had a memorable Thanksgiving dinner at his house where he sat our daughter Kathy, then almost five, on his lap and braided her hair in an approved Swiss fashion. He influenced and shaped me for years after we left Madison fifty years ago.

He was just magic.

Charles H. Holbrow

two men stand next to each other, one holding a bust of his own likeness
Charles H. Holbrow and Willy Haeberli at the Haeberli Fest symposium, June 10, 2005 | Credit: Jim Hanesworth (supplied by Charles Holbrow)

I met Willy Haeberli for the first time in 1958-59 when I took his course on electricity and magnetsim (Physics 104a,b). He was a fine teacher, careful, thoughtful, and lively. I remember with special pleasure his elaboration of the curl and divergence in Cartesian coordinates.

Later, after I joined Heinz Barschall’s research group, Willy and his group were neighbors in our wing of Sterling Hall, and, as was the case for so many of us who had anything to do with him, Willy became my lifelong friend. Over the years I came to Madison often, and my wife and I would usually have a meal with him and Gabi either at their splendid house overlooking Lake Mendota or in some café on The Square. I especially appreciated his efforts that kept Heinz affiliated with the University after the 1970 Bombing. After Heinz died in 1997, Willy became my strongest link to Wisconsin physics. I mourn his passing and the breaking of that link.

Steve Vigdor

I was a graduate student of Willy’s from 1967-73. It was the heyday of experimental nuclear physics based on the Tandem Van de Graaff laboratory in Madison. There were 40 or so graduate students in the groups headed by four faculty members (Haeberli, Barschall, Herb and Richards). We students were a close-knit group, with charismatic leadership from Jay Davis. We learned from each other. We strongly bonded over “In case of Bromley” bowties, Christmas colloquia, and the painstaking rebuilding of the tandem after the misguided August 1970 bombing.

Willy helped to transform me from a bright but very green teenager with no research experience into a careful, self-confident experimental physicist and young man, one with enough presence of mind to filibuster my way out of Vietnam in front of my Bronx draft board and to stimulate an argument among my examiners that filled precious minutes of my Prelim Oral. Willy trained me in elegant equipment and experiment design.

Willy pioneered the design and construction of polarized ion sources. Like many of his students, I began working on the construction of a new source, one already in progress, but underperforming, when I joined the group. The first task Willy assigned me was to go through the source development log book in search of miscalculations that might explain the underperformance. I didn’t find any. But Willy brought me up to speed on the need for vigilance when he phoned me at home on a Saturday evening, in the middle of a party my roommates and I were throwing, to say how disappointed he was that I’d missed an error he subsequently found in the log book.

I then advanced to work on spin experiments using the source I’d helped to build. I had already collected the data originally intended for my Ph.D. thesis by the time of my marriage in June 1970. But then the bombing happened. The data I’d collected with the help of a more senior student in the group, Bob Rathmell, became his thesis data when his own log books and tapes were destroyed in the bombing. After our six months of around-the-clock work to rebuild the tandem, Willy suggested that I find some other suitable nuclei with which to demonstrate that the effect we’d found in that first experiment was a systematic feature. I suggested two nuclei, but Willy urged me to find more. By the time my dissertation was completed in summer of 1973, he told me “You know you could have finished much sooner if you hadn’t insisted on making measurements on so many nuclei.”

The well-rounded experience provided by my thesis research was invaluable. I designed the experiment and the target and detector hardware, assembled the electronics, wrote software for data acquisition and analysis, operated (and frequently repaired) the accelerator, interpreted the results and wrote the papers reporting them. The familiarity I gained under Willy’s mentorship in all aspects of experimental physics strongly fueled my subsequent career.

Willy also trained me in the art of writing scientific papers with Swiss precision. In return, I taught him that semi-classical models could be right more than half the time. The drafting of papers we co-authored often involved a battle of strong wills, highlighted by hours-long arguments over the use of passive voice, the appropriateness of hyphens, the placement of commas. In the acknowledgments for my Ph.D. dissertation I thanked Willy “for his wisdom, his guidance, and his heroic suspension of instinctive critical faculties during the reading of this manuscript.” I loved him for all aspects of his guidance.

Willy pioneered a subfield of nuclear physics measuring spin polarization phenomena. That subfield represented a small corner of the field when I was a graduate student, but expanded gradually over the decades since to become a major theme in forefront research. Willy himself played critical roles well into his eighties in several areas of that forefront research, providing wisdom, penetrating insights, and elegant polarized sources and targets for important experiments at the Indiana University Cyclotron Facility (IUCF), the HERA collider in Hamburg, and the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). Now the field looks forward to its next major project, a polarized ion-polarized electron collider (EIC), continuing Willy’s legacy.

I did my own spin physics research largely at IUCF and RHIC, and helped to lay the groundwork for EIC. At IUCF I helped to establish a strong nuclear physics group including several former Wisconsin students and post-docs: Peter Schwandt, myself, Hans-Otto Meyer, Ed Stephenson, Jim Sowinski. I went on to oversee all of the nuclear and particle physics research at BNL. I owe much of the success of my own career to Willy.

I remember fondly occasional Saturday morning group meetings in Madison when, rather than discussing progress on ongoing research, Willy would lead the group in a brainstorming session to think about challenging, speculative experiments – near or beyond the available technical limits — to test one or another aspect of fundamental interactions. He encouraged me to think about one of these “impossible” experiments as a thesis project, but I decided I wanted to get my degree in less than a decade. However, I retained the tendency to conjure up “impossible” experiments throughout my own career, even pulling off a couple of them, though many more concepts remain gedanken.

I have been able to return to Madison to visit Willy only a few times this century. While his body began to physically fail him, he remained intellectually sharp and interested in my own career. Along with many others at his retirement celebration, I visited his beautiful, art-filled home on Lake Mendota.  Over the past five years or so, I remained in occasional e-mail contact with Willy. He remains one of the most important influences on my own life and I will miss him greatly.

Bob Cadmus

Willy was such a remarkable, multidimensional person that it’s hard to decide what snippets of experience to contribute to this tribute.  Of course, as my thesis advisor he was a wonderful scientific mentor, but two other things had an enduring effect on my career.  One was the opportunity to work with Willy and Ugo Camerini on the creation of the “Physics in the Arts” course during which I learned so much and which led to the creation of a similar course in my own teaching career.  The second was the extent to which Willy taught me how to write science.  Once when discussing a manuscript he said that a passage was not clear enough. His explanation, which is front and center today when I write papers and when I talk to students about writing, was that it is not sufficient for writing to be clear enough to be understood, but that it must be so clear that it cannot be misunderstood.  He will be missed but his influence lives on.

Francis Halzen

When I joined the highly successful launch of Physics in the Arts by Ugo Camerini and Willy Haeberli as a junior partner, I soon ran into problems due to my use of computer software to replace “real” experimentation in the laboratory. The ensuing debate revealed Willy to be a passionate physicist and a caring and truly passionate teacher. Before every lecture, Willy would isolate himself in his office to concentrate on delivering the ultimate lecture. I felt guilty for not following his example, but he was too much of a gentleman to imply that I should. Even before, and long after, Willy was always a caring and very wise counselor to me. I miss our long lunches at Sunporch and the gourmet dinners that he prepared with scientific precision; I miss him.

David Kocher

I first met Willy in a graduate-level course he taught on experimental nuclear physics.  In his lectures, it was soon apparent that he had a rare ability to explain complicated concepts and ideas in the simplest possible terms.  This was the kind of teacher I wanted to work with.  During my years in working under Willy’s guidance, some of my most meaningful experiences involved our collaborations in writing papers on our research.  We would sometimes spend several minutes haggling over how a single sentence should be written to convey the point in a manner that could be easily understood.  These experiences impressed upon me the importance of always striving, in writing and in speaking, to “say what you mean, mean what you say, and get it right.”  This is a lesson I have never forgotten.

Willy was a true visionary and pathfinder, always coming up with new ideas and ways of advancing the science, such as the development of polarized ion sources during my time in his group.  On one occasion, we devised an approach to use measurements of the vector analyzing power in (d,p) stripping reactions on odd-A nuclei initiated by vector-polarized deuterons to determine the relative cross-section contributions of two possible angular momentum transfers to a particular final state in the residual nucleus.  The only time Willy came into the control room during one of my running periods was on the day I made the first measurements to test our approach.  He looked at the initial results, saw that the approach worked, and left with a look of satisfaction on his face (and on to his next idea).

Other remembrances of Willy have nothing to do with physics.  During the height of the hippy craze in the 1960s, several of us students wondered what Willy would look like with a beard.  So, we struck a bargain with him that all of us would forgo shaving for a period of time (six weeks, maybe?) if he would do the same.  He agreed to this, and I believe he at least kept a mustache ever since.  One of my enjoyments in Madison was attending classical music concerts.  One year, the Guarneri string quartet played all 16 of the Beethoven quartets in a series of concerts.  I was quite awed by these performances, and Willy and I had conversations in which he shared his views of their work (he, too, loved music).  During a visit a few years later, he even tolerated my attempt to play the cello one evening at his home shortly after I began taking lessons.  Right before I left Madison, my parents came for a short visit, and Willy was most gracious in spending time with them and making them feel welcome.

As others have commented, one of the lasting rewards of being part of a larger group headed by the nuclear physics professors at UW was the sense of camaraderie among the graduate students and post-docs, with the more senior members passing their knowledge and experience on to the newbies.  We were all in this together—to me, there was nothing quite like having to do tank maintenance and other joint responsibilities in developing and maintaining equipment we all used in our research to promote this feeling.  These relationships with former colleagues have been cemented by the several reunions we’ve had over the years.

I have often thought that the great lesson from my experience in Willy’s group was learning how to do science with thoughtfulness and integrity; how we did it was more important than what we did.  I especially developed an interest in finding and describing nuggets of basic truth in masses of information (seeing the forest for the trees), which has served me well in my career in health physics.  For this and many other reasons, it is an honor to have an opportunity to remember Willy on this occasion.