Memories of James W. Cronin

Alan Watson
University of Leeds; Colleague and friend
October 1, 2016
James Cronin and Alan Watson
James Cronin (1931–2016); Nature, v. 537

Ken Bloom
University of Nebraska-Lincoln; Got to know him a little when I was an undergrad
October 1, 2016
Jim was the first Nobel laureate that I ever met. (I recognize that this is a funny thing to say unless you are a physicist or went to the University of Chicago.) I never worked with him or for him, but he was a presence when I was a Chicago undergrad (1988-92) and working in the HEP group. When I learned who he was, I was somewhat in awe of him, but he turned out to be the nicest guy, always friendly and interested in what I was doing. When he saw me looking at a plot, he wanted to know what it was. (It was nonsense, actually.) Whenever I would meet Jim after I left Chicago, he would remember me (or at least pretend to) and ask about my work. He helped create the intellectual atmosphere at Chicago that made it such a great place to work and learn, and I very much appreciate that.

Toshihiro Fujii
ICRR, University of Tokyo; Colleague
October 1, 2016
Welcome remark in KICP workshop: Next-Generation Techniques for Ultra-High Energy (UHE) Astroparticle Physics (February 29th 2016)
I would like to share photos of Jim's final lecture in the workshop at KICP. Jim told us we really need next-generation observatories to observe UHECRs with 10 times larger statistics in order to find the UHECR origins.

Fortunately, I spend in Chicago with Jim in recent three years. We have a couple of chances to sit together and discuss science, next-generation cosmic ray observatory and also life in Chicago.

Jim always encouraged me to develop new detectors and ideas. I think Jim really would like to find the UHECR source. I copied Jim's last e-mail to me in March 2016,

''I hope you can bring the single-pixel fluorescence detector to practical application. While most of my colleagues are pleased with the results of Auger, I am disappointed we failed to find sources.
Instrumentation like yours may make that possible some day. I wish you well in your scientific life and as important your personal life!

All the best,
Jim Cronin''

We should do our best to solve Jim's homework which is to conclude UHECR sources.

With deepest sympathy.
Toshihiro Fujii

Welcome remark in KICP workshop: Next-Generation Techniques for Ultra-High Energy (UHE) Astroparticle Physics (February 29th 2016)  

David F Nitz
Michigan Technological University; Colleague and friend
September 28, 2016
I first got to know Jim around 1986 or so when I started working in cosmic rays with Dan Sinclair, Jack Van der Velde, and Jim Matthews at the University of Michigan and we started collaborating with Jim on what became the CASA-MIA array.

Afterwards we continued to collaborate on the Auger Observatory project, right from the earliest days.

He was always extremely helpful to me in my professional life. I'm certain I would not be where I am now if it where not for the continued encouragement and support of Jim to open doorways for me.

Early on he provided funds from UNESCO so that I could travel to help drum up support and collaborators for Auger.

In the early days of Auger he would bring me along on travel as a technical expert. I remember especially one visit with him to Washington where we visited both the Office of Science & Technology Policy (OSTP) and Orrin Hatch. Oren & Jim charmed each other.

On another occasion (in 1995) I traveled with Jim to Bariloche, AR, to meet with Argentine & Brazilian colleagues. During a visit to the Physics Institute in Bariloche on that same trip, Jim noticed and excitedly pointed out that the Van de Graff accelerator there was the very same one he used as a graduate student at U. Chicago.

Special memories include some evening nightcaps with Jim, Alan, and Jim Matthews, where we would imbibe in a wee bit of scotch. I had to learn to like scotch, but it was well worth it.

Bruce Dawson
University of Adelaide, Australia; Colleague
September 27, 2016
My memories of Jim Cronin center on his enthusiasm for physics, his steadfast commitment to the Pierre Auger Observatory, and especially his encouragement of young physicists. I've seen Jim interact with graduate students and postdocs many times over the years, where he always showed genuine interest and kindness.

I first met Jim in October 1985, three months after completing my PhD. I had moved from Australia to the US, taking a postdoc at the University of Utah on the Fly's Eye experiment. One of my first jobs was working on a design of the ''Utah array'', a scintillator array that would complement the Michigan underground muon array, MIA, being built at the Fly's Eye site at Dugway Proving Grounds. My boss, George Cassiday, was visiting the Michigan group. As it turns out, Jim was also visiting Michigan. George called me on the phone to tell me to jump on a plane so that I could show Jim my work on the array design, in particular a Monte Carlo program I'd written to simulate the array's response to cosmic ray air showers. This must have been at the time Jim was starting to contemplate the CASA experiment.

I was nervous and very excited about meeting Jim, especially since he was the first Nobel laureate I'd met. (George seemed surprised at this at first, though he soon agreed that Nobel laureates weren't thick on the ground in Adelaide!) But Jim made me feel very relaxed as we spent a couple of hours discussing the simulation code, the inputs and the assumptions. It was written in FORTRAN (which Jim
appreciated) and the code was commented (not so important for Jim). I remember very clearly his deep interest in what I was doing, his humility in learning the basics of a new field, and his kindness in expressing his appreciation.

This was the beginning of many interactions between us over the next 30 years. Early happy memories include sharing lunch with Jim and his daughter Kathy at the cosmic ray conference in Moscow in 1987, and Jim's two visits to Adelaide in the early 90s during the ramping up of Auger. The beginnings of Auger were extremely exciting as we designed the observatory. Jim was initially skeptical of the need for fluorescence detectors, but once he saw the benefits he was enthusiastic and immensely encouraging of our work in designing a hybrid observatory. Such was his influence on me that I remember a whole decade where I used to wake up in the middle of the night worrying that I was letting Jim down by not producing some plot or other!

I know I am just one of hundreds of people who have benefited in their career and their life through knowing and learning from Jim Cronin. His legacy is enormous, and his passing has left a big hole in our lives.

Lawrence Wiencke
Colorado School of Mines; Colleague
September 26, 2016
Jim Cronin with Lawrence Wiencke at the Pierre Auger Observatory Central Laser Facility (March 2004, photo Patrick Younk)
This is a photo of Jim standing with me near the middle of the Pierre Auger Observatory in 2004. The photo was taken by Patrick Younk. The white structure in the background is the central laser facility (CLF) of the observatory. The device directs a laser beam into the atmosphere and the scattered light appears as a track in the Observatory's optical detectors. About a year earlier Jim had arranged support for me through the University of Chicago to participate in the Pierre Auger Observatory. I got involved in the CLF installation. Looking back, that opportunity opened a lot of doors for me and I owe a lot to Jim. On the day of this photo, there was some maintenance work to do at the CLF. Jim was available to go along to help for the day. Driving out there, Jim told me that his favorite days were when he got to go into the field and work on something. This picture has always been special to me, and now even more so. My thesis advisor, Bruce Knapp, was one of Jim's PhD students.

David G Cassel
Professor of Physics Emeritus, Cornell University; Former student, colleague, and friend
September 24, 2016
Fig. 1 Schematic illustration of the spark chambers and typical tracks in an event with lambda decay. From Phys. Rev. 129, 1975 (1963). Used with permission.
Jim Cronin’s colleagues, whose personal experience with him is only in more recent years, may not be familiar with the profound impact that his pioneering development of spark chambers had on physics in the 1960s. His influence was particularly strongly felt in the Elementary Particle Physics Laboratory at Princeton in the early 1960s, when he was a faculty member and I was a graduate student.

Val Fitch brought me into the lab in the fall of 1961, at the start of my second year as a graduate student. He had already proposed an experiment that eventually became my thesis topic, scattering of high energy charged pions on atomic electrons to measure the pion’s charge radius. Originally the experiment had been envisioned as a hodoscope (an array of scintillation counters) to detect the scattered pions and electrons. However, by 1961 Jim’s outstanding success with spark chambers made them the obvious choice. In an experiment in which measurement of small angles was required, the high position resolution and fine granularity of spark chambers were a vast improvement over counter hodoscopes. For this and many other experiments, the ability to select which events to record was a decisive advantage over bubble chambers, which had even better granularity and resolution. Although high resolution, fine granularity, and event selectivity of detectors are routine now, they were truly revolutionary in the early 1960s.

By the time I entered the laboratory, Jim had already initiated an extremely successful program encompassing all stages of building and utilizing spark chambers. Today we would call it vertical integration. The centerpiece of his spark chamber design was aluminum frames with thin aluminum foils on both sides that were relatively easy to produce in almost any size and aspect ratio. The thin foils were utilized to minimize multiple scattering, in order to enhance measurements of track angles and positions. Furthermore, various scattering materials, particularly carbon and lead, could be inserted in the frames between the foils to provide information about the detected particles beyond just their angles and positions. Jim and his students had utilized a chamber with plates loaded with carbon to measure proton polarization and a different chamber with plates loaded with lead to detect the extra sparks near a track as evidence for electromagnetic showers to identify electrons. Most graduate students in the lab voted with their feet by choosing to work with Jim, thereby verifying the excitement and vitality of his spark chamber program and his outstanding qualities as a mentor.

At that time, not everyone was successful with spark chambers. Once Val mentioned that conventional wisdom held that spark chambers could only work with Jim Cronin’s “spit.”

In a particularly beautiful experiment, Jim and Oliver Overseth measured the three weak decay parameters of the lambda hyperon. They used a system of spark chambers (illustrated schematically in Fig. 1) to detect lambdas produced by negative pions incident on protons in a polyethylene target. The incoming pion was visible in a chamber that included some plates loaded with polyethylene. After a lambda traversed several plates with no visible tracks, the proton and negative pion from the lambda decay were clearly visible as a V. Measurement of the polarization of the protons was required to determine one of the decay parameters, so some of the downstream spark chamber plates were loaded with carbon for that measurement. I thought then, and still think now that this was one of the most beautiful spark chamber experiments ever done.

Once I told Jim that I felt that this experiment was particularly beautiful and that the paper was especially well-written and informative. With characteristic modesty, Jim admitted that he had written the paper with the education of graduate students in mind.

When Val and I decided to utilize spark chambers in my thesis experiment, we built two spark chambers closely following Jim’s techniques and methods. Jim generously and enthusiastically supported our effort by answering every question we had and anticipating some that we did not know we should ask. Much of the fabrication of the chamber was in the hands of the master machinist/technician that Jim had brought into the lab and with whom he developed his chamber technology. Jim’s spark chamber technology is illustrated in Fig. 2, which shows the larger of the two spark chambers built for my thesis experiment.

When we had data on film from our run at Brookhaven, Jim shared the measuring machines that he had developed with the same technician. These machines were much less expensive than the conventional machines developed for accurately measuring bubble chamber film. The machines were a tribute to Jim’s ability to focus on essentials and find the simplest and least expensive way to accomplish his goals. Each machine was a large plywood box fitted with with a film holder and lens that projected an image of film frame onto a glass/mylar screen. The operator utilized a drafting machine, commonly used on drawing boards in those days, which could move a hub over the area of the screen without loosing track of the angle of the hub. The hub was fitted with an angular encoder and a glass straight edge. The angle of a track was measured by placing a line etched on the straight edge along the track and pressing a foot pedal to record the angle of the straight edge on an IBM card. Furthermore, the position of the first spark in a track was measured by recording the angle of a line through the track and a specified fiducial mark on the image. This device measured angles with an accuracy of 1 milliradian, sufficient accuracy for most spark chamber experiments at that time.

Jim was exceptionally generous, warm, and outgoing. These qualities went a long way toward defining an atmosphere in the lab that was exceptionally encouraging and nurturing for graduate students. Although I was not his thesis student, Jim routinely included me in parties for his own students. He was always free with his advice and thoughts on any important matter, technical or not. This was particularly useful for me when I was considering an offer from Cornell. Earlier, Jim had been to Cornell to expose a spark chamber with lead inside the plates to an electron beam. He came back very excited with the style of the laboratory and the ability of the staff to make the most of relatively modest resources. I particularly remember his enthusiasm in telling me that the Cornell staff had provided a farmer — who had lost one arm in an accident — with the opportunity to develop into the best operator of their accelerator. My memory of this earlier conversation helped to validate the positive impression that the Cornell group made during my recruiting visit, so I was ready to accept an offer from Cornell when it came.

After finishing my thesis, I spent the 1965 calendar year as a postdoc at CERN. Later in that year, Jim went to Paris on a sabbatical leave to work with Rene Turley at Saclay, and I visited them in Paris. At Saclay, Rene told me that some part of the spark chamber that they were constructing did not quite fit. In his usual style, Jim picked up a file and started to work on the offending part. The French technicians could not believe their eyes when they saw such a distinguished American professor working with a file. After that experience, the technicians would do anything for him that they possibly could.

That day we had lunch in the Saclay cafeteria. I stood in the line with my tray, trying to puzzle out how the system worked. Jim humorously observed that there is nothing else as confusing as an unfamiliar cafeteria line and then guided me through the process.

During the early years of the CESR/CLEO program at Cornell, Jim led the Program Advisory Committee (PAC) to advise the laboratory director and the National Science Foundation. In these visits to Cornell, I again experienced the warmth and openness that were so familiar from my graduate school days. Furthermore, Jim’s advice was sound and he was highly respected. This proved to be crucial in one particularly important matter. Determining whether charged tracks were pions, kaons, and protons was difficult for high momentum tracks. This led to three different choices of devices, which were implemented in eight “octants” surrounding the central solenoidal CLEO detector. After we had some experience with these devices, in his PAC report, Jim told us — quite firmly — that we had to choose a single device for all octants, so the detector would be symmetric and we had to master and service only one technology. He did not try to specify which device we should choose, only that a choice was necessary. This led the somewhat feisty CLEO group to finally choose a single detector technology for particle identification.

Jim’s modesty is frequently mentioned by others. Once he told me that he was not sure that he could have made it as a graduate student if he had tried to be one of the many brilliant thesis students surrounding Fermi. Having already experienced Jim’s intelligence, breadth, and depth, I had a hard time believing that he might not have flourished with Fermi. Years later, as the Auger Observatory was starting to provide significant measurements of the spectrum of ultra high energy cosmic rays, I felt that Jim was a perfect candidate for the Bethe Lectureship, Cornell’s most distinguished physics lecture series. When I tried to interest him in this appointment, he responded by telling me that other colleagues in the Auger collaboration were much more appropriate. I appreciated his modesty and willingness to propose colleagues for this distinguished role, but I was sorry to loose the opportunity to share my experience of Jim’s intellectual depth, generosity, and warmth with Cornell graduate students.

My last experience with Jim was at the memorial for Val Fitch, held a little over a year ago. In a moving tribute, Jim spoke very warmly and affectionately of his relationship to Val over all of the years from their earliest to the very recent past. This was a fitting memorial for both of them, demonstrating how they were able to work together so effectively to discover CP violation.

Fig. 2 The larger of the two spark chambers built for my thesis experiment utilizing Jim Cronin’s technology. The Tide box in the background illustrates the scale.  

Miguel Herrera
the head principal of the James W. Cronin school in Malargüe; Colleague, friend
September 20, 2016
Memories from James W. Cronin School in Malargüe, Argentina

I have been the head principal of the school since 2012, but also a teacher at the school since its beginning (2001). The first thing that comes to my mind about Jim is when I went to the observatory with former head principal Stella Campi to meet Paul Mantsch and ask if there was any possibility to have the school named after him.

Then, when the official naming ceremony was held, I had my first opportunity to meet him and then later when the school was under construction and finally at the inauguration of the new school building (2006).

I can still remember every spot where he got photos taken with the students.

His loss has been very hard on every one of us, faculty members and students, that had the opportunity to meet him. He will always be in every classroom and around the gallery.

I said the last goodbye in 2013 on his last visit to Malargüe, when he specially told me that he wanted to visit the school for the last time, since he wasn't planning to come back...

If you want to feel Jim's presence... just come and visit the James Watson Cronin School at Malargüe, Argentina.

His Mail.....

Dear Miguel,

I will be coming to Malargüe for the Auger next week. I would like to visit the school. As I am 81 years old and have some mechanical problems with my left knee this may be my last visit to Malargüe.

On another point. Can you tell me how old is Rosa's baby and is it a boy or a girl?

I look forward to seeing you next week!

Jim Cronin

Kavli Institute for Cosmological Physics
Enrico Fermi Institute
5640 S. Ellis Av.
Chicago IL 60637


Beatriz Garcia
ITeDA; Friend
September 18, 2016
Alberto and Jim at Potrerillos, Mendoza
This memory is not from Malargue, the Pierre Auger Observatory or the work to install the detectors, but it is about a travel that we made to the Uco Valley, in Mendoza, to visit a winery. We went with Cristina Raschia, the director of 3 of the Pierre Auger videos, and Alberto Etchegoyen. I remember very well this travel, because the beautiful day and the very good company.
Now, when I am revisiting this photos, I can not believe that Jim is not any more is an strange like his is still with us, through these memories, but also through his humanity, humility which will never die in our minds. I decided write ''friend'' at the box about ''relationship'', at least to me this this is right.

Jim tasting a good wine in MendozaJim and Alberto at Salentein, in the middle of the wine-yard 

Beatriz Garcia
ITeDA; Colleague
September 18, 2016
Jim Cronin checking his conference at Palmares Bureau.
Several times, during the Jim's visits to Mendoza, different institutions invited him and organized conferences for different audiences. In 2005, Los Andes newspaper organized one for more than 300 persons at Palmares open mall. I was there, and the connection between Jim and the public was incredible and unforgettable.

Jim Cronin in action.  

Beatriz Garcia
September 18, 2016
Pierre Auger Observatory Visitors Center. James Cronin, Cristina Rachia and B. Garcia.
As part of the cerebration of the international year of Physics, in 2005, we made under the direction of Cristina Raschia, the first institutional video of Pierre Auger Observatory, Messengers from the Space. The images were taken in 2004 and Jim Cronin was the main character in this production; part of these days are alive on these images.

Messengers from Space crew.James Cronin and Carlos Hojvat at the VC of the Pierre Auger Observatory 

Marco Aglietta
September 15, 2016
Dear Paul, dear colleagues,

with deep emotion, following the suggestion of Paul and hoping to please everyone, I send some images of Jim to testify his great love for Auger, Malargue and its people.

The first photographs date back to September 2005 (courtesy of Silvano Gallian). At that time, I was in Malargue for a routinely SDE shift and I was going to make some measurement in the field. Jim was at the Observatory too and he asked me to participate at these activities, as he was interested in experiencing the difficulties of working in the field.

So the next day, early in the morning, we left the Observatory to visit some detectors. As often happens in these special occasions, the trip was characterized by all kinds of mishaps (see pictures Sep2005_1 to Sept2005_4), contingencies which however did not prevent us to work with great satisfaction and fun (pictures Sept2005_5 and Sept2005_6). Thanks to Jim's great empathy and spontaneity, the atmosphere within the team immediately turned out to be friendly and positive to the point that we dared to invite him at the dinner we organized at Javier Alcaja's home for the following night (pictures Sept2005_7 and Sept2005_8). During that unforgettable evening, Jim told me that it was the first invitation he ever received by a family in Malargue and that he was really touched by the warm welcome he received. He also gave a short speech, where he emphasized the great luck that had led to prefer Malargue among all sites considered as possible candidates for Auger South and this especially for the generosity of the people encountered. How much this first experience as a member of the SDE team had amused Jim, it is demonstrated by the e-mail he sent me almost five years later when he realized that his participation to the annual meeting of the Argentine Physical Society (held in Malargue in September 2010) was, by chance, in coincidence with another of my frequent SDE shifts.

From: Jim Cronin
19/07/2010 14:58
Dear Marco,
I am really pleased that you will be coming to Malargue to work on the PMT's. I think I remember when I had the pleasure of going out in the field with you. I will be in Malargue around Sept 29 for the Argentine Physical Society meeting and hope to see you then.
Jim Cronin

This time, knowing Jim's request in advance, the trip in the field was better organised and many components of the SDE staff wished to attend. A rough big 'asado' was then prepared, exploiting the kind hospitality of a family living in a small 'puesto' lost in the pampa (pictures from Sept2010_1 to Sept2010_5, courtesy of Antonio Zampieri). Jim was so enthusiastic about this unexpected visit to include the episode inside his talk at the AFA meeting where he also showed the funny image with him together with the landlady (Sept2010_6).

That's all. I really hope these pictures can be a strong incentive for our younger collaborators, especially now that we need a big effort in the field.
Please feel free to add my comments and/or photographs to the recollections and stories about Jim and the Auger Observatory you are preparing.

Best regards,


Paul Mantsch
Fermilab; Colleague, friend
September 14, 2016
An Pierre Auger Collaboration meeting in Malargue, Argentina - 2006 - Events at the Auger Celebration 2005
Jim Cronin and the Pierre Auger Observatory

Paul Mantsch – 30 August 2016

It was a great privilege and honor to work with Jim Cronin on the Pierre Auger Observatory. What follows are some of my recollections of the events that, under Jim’s inspired leadership, led to the construction and operation of the world’s largest cosmic ray observatory.

It was late fall of 1993, a few weeks after the US congress had terminated the Supercollider. Having invested eleven of my most productive years on the SSC beginning with its conception in June of 1982, I was still recovering. However, what came next was exciting and in the end much more rewarding, the defining challenge of my scientific life.

I remember the day clearly, as it set my course for the next twenty-two years. I heard that Jim Cronin had just visited Fermilab’s director, John Peoples and discussed the possibility of Fermilab hosting a workshop to design a huge cosmic ray air shower detector, ten times bigger than anything built up to that time. The new cosmic ray detector would record particles hitting the earth from space with energies 10 million times more energetic than even the Supercollider would have produced. Now this news instantly struck a responsive chord as I had a latent interest in cosmic ray physics since my undergraduate experience working part time in the Cosmic Ray Laboratory at Case.

On hearing of Jim’s idea, I knew instantly that I had to be part of this new, exciting project. I knew Jim slightly and wasted no time finding a phone, calling him and offering help. Jim was obviously pleased and a few days later came to Fermilab to discuss his ideas with a small group of like-minded colleagues I had rounded up. I remember our asking lots of questions about how one would possibly measure the properties of cosmic rays by detecting a few particles that reached the ground. Jim explained all of this with great enthusiasm and later sent us a stack of papers, including those from a recent cosmic ray conference in Paris. We were hooked. Poring over the papers, we were soon excitedly imagining designs for cosmic ray particle detectors that could be spread over thousands of square kilometers to capture these strange messengers from the cosmos.

The idea of a very large cosmic ray detector had been germinating for several years. In 1991 Jim Cronin, who had developed an interest in cosmic ray physics and Alan Watson, a long time cosmic ray physicist from the University of Leeds got together at an international cosmic ray conference in Dublin. They concluded that the only way to address the cosmic ray questions head on was to build a huge array of detectors, perhaps 5000 square kilometers in area, which would have a chance of gathering enough cosmic ray events above 1019 electron volts to provide some answers. The Giant Array Project was born.

The project gathered headway over the next few years as Cronin and Watson described their vision in talks at meetings all over the world where cosmic ray physics was on the agenda, including cosmic ray conferences in Adelaide in 1993 and then in Paris in 1992. By the time Cronin visited Fermilab in late 1993 the idea was beginning to take on a serious form.

Cronin’s idea for a six-month Giant Array Project design workshop at Fermilab was inspired. The workshop would be open to researchers in the cosmic ray physics community and related fields, some to share their insights and experience and others who might want to be part of the project. All could participate in the planning the Observatory from the beginning, equal partners in developing the design.

We began planning the Giant Array Project workshop during 1994 with the approval and encouragement of the Fermilab director and the help of the Fermilab staff. I organized the details of the workshop while Cronin started inviting researchers from around the world to participate, noted experts in astrophysics and cosmology both theorists and experimentalists who would bring their knowledge to help shape the design. Visitors would come a few days or a few months to exchange ideas and refine the design. With his reputation (and charm) Jim was able to attract researchers from 40 universities and laboratories from Argentina, Armenia, Australia, Bolivia, Brazil, Czech Republic, China, Greece, Italy, Mexico, Poland, Romania, Slovenia, the UK and, of course, the US. It was an eclectic group of high-energy physicists, nuclear physicists, cosmic ray physicists, and astronomers. Many of these countries had a tradition of cosmic ray physics but often did not have the means to participate in the costly world of high-energy physics accelerators.

The excitement associated with the power of the unique international collaboration that was forming began to sink in toward the end of the workshop when Jim and I discussed possible involvement of groups from many countries from around the world, talking individually to research groups from each of the countries that attended.

As more detailed objectives and requirements of the project began to take shape, competing design approaches evolved. Our approach to the design was to allow a “thousand flowers bloom” then choose the best design ideas among them.

Indeed, there were many ideas. With the help of some Fermilab colleagues, I had built two 32 square foot prototype detectors using large number of sheets of scrounged scintillation plastic. My Fermilab colleague, Peter Mazur, designed detectors using a technique involving resistive plate chambers. Another group in France was working on a scintillator/lead/scintillator sandwich, which become known as the leadburger. Alan Watson argued for a water Cherenkov detector similar to the one he had used at his Havarah Park array in the 1970s and 1980s.

After a close look at the costs and the likely performance of the different candidate detectors, we decided on simple, proven, water Cherenkov detectors, which were also quite benign to the environment. After more discussion, we decided to augment the water detectors with air fluorescence detectors, a technique that had been pioneered by the University of Utah for their Fly’s Eye detector.

There would be two sites, one in the northern hemisphere and one in the southern hemisphere so that, as the earth turned the Observatory would gather cosmic ray events from the whole sky.

During the workshop, it was agreed that the name Giant Array Project lacked style and that it would be better to name the Observatory after Pierre Auger in recognition of his beautiful, pioneering cosmic ray experiments. The collaboration quickly adopted the name and we launched the Pierre Auger Project to build the Pierre Auger Observatory. The ideas developed in the workshop were summarized in the Pierre Auger Observatory Design Report. The design report included a complete design and a detailed cost estimate for both the construction and operation of the Observatory.

The Observatory in Argentina was built almost exactly as described in the design report and, in retrospect, it was so successful were we to start again, we would change little. A possible improvement would have been to make it even bigger.

The collaboration that emerged during and after the design workshop now consisted of about 69 institutions in 17 countries spread over Europe, North and South America and Australia. No country dominated with the maximum contribution of any one country to construction being less than 25%. Another feature, and a concern of some, was that the project was not anchored to some strong institution that could provide financial stability as that enjoyed by the big collider detectors at established national high-energy physics laboratories. Indeed a suitable model for such an international partnership did not exist. The collaboration we were organizing for the Auger Project was unique.

Most of the collaborators were not used to the discipline required for a project of this scale and many, if not most, were deeply suspicious of what they perceived as mostly unnecessary, indeed counter-productive, bureaucracy. One of those was Jim Cronin. Like Jim, most collaborators were used to working with small groups of five to ten researchers with no real organization so that the research team could communicate daily and make decisions easily.

I drew up the organization chart based on what I had learned about managing projects over the years at Fermilab and in the SSC work. I gave it to Jim who reluctantly showed it to the developing collaboration at the workshop, beginning his talk with: “I am really embarrassed to show this.” In time, Jim would come to appreciate the basic need for the organization, particularly as building the Observatory evolved.

Jim was the obvious choice for spokesperson. I was hoping that he would ask me to be co-spokesperson. However, having accepted my arguments for the need for a workable project management, Jim was certain that I should be project manager. I later regretted the designation project manager as reporters assumed that I was someone with a shovel and yellow hardhat. Mostly as the result of Dilbert cartoons, the term manager and management have assumed distinctly negative connotations. Nevertheless, I bore this title for the next 20 years.

The search for a suitable site got underway almost immediately after the Fermilab workshop using funds from a grant that Jim Cronin was able to obtain from William Grainger, a Chicago industrialist and from UNESCO. With the physical site requirements developed during the workshop in hand, a team of collaborators evaluated prospective southern hemisphere sites in Argentina, Australia and South Africa. Northern hemisphere site possibilities included Mexico, Spain and Utah and Colorado in the US. The site selection was based primarily on these requirements and on the scientific support from the host country. The evaluation team used a set of instruments to evaluate the clarity of the sky, an essential consideration for the fluorescence detectors, by measuring the atmospheric attenuation of star light. An important, but secondary, consideration was the value of incentives that a potential host might offer.

Having a design in hand and with some suitable sites identified, the next task was to decide on the final sites, form a collaboration and then persuade the funding agencies in the collaborating countries that they should approve and share in the $100 million cost. The process turned out to be both lengthy and painful.

In November of 1995, UNESCO also hosted the first Auger collaboration meeting at its headquarters in Paris where the collaboration was formed and the site was selected for the observatory in the southern hemisphere. An Auger Collaboration Board was formed that included representatives of the institutions of those countries that attended the meeting.

The site was selected by an election, with each country in the new collaboration having one vote. After an extensive discussion Argentina was selected, both because of the enthusiastic support of scientists there, led by Alberto Etchegoyen, the generous offer of funds and a suitable site to be offered by the president of Argentina, President Carlos Menem who had succumbed to Jim Cronin’s persuasion (and charm) in an earlier visit to Buenos Aires.

We finally had a good look at the site in Argentina during a visit in September 1996 at a collaboration meeting set at a small resort near the city of San Rafael. The meeting was not far from a vast open plain called the Pampa Amarilla (yellow pampa) where we soon would deploy our detectors over an expanse of 1000 square miles of flat dry land.

After a tense period of finding the necessary funds involving sometimes painful reviews, we prevailed for the Argentina site, due in large measure to Jim Cronin’s boundless energy and enthusiasm. Prototype detectors began to appear at the site in 2000 with serious construction beginning in 2002. The first data taking began in 2004 even before the Observatory was completed in 2008.

More than 64 journal papers have been published based on Auger data that is shaping the future of astroparticle physics. At least as important is the training of young physicists for the future. From among the Auger collaborators, 267 PhDs have been awarded with more than 100 more in the pipeline.

While Jim Cronin has a large and stellar scientific legacy, the Pierre Auger Observatory will be one of the brightest stars.

Steve Francis
Former student
September 10, 2016
It was the first day of our undergraduate solid state class, probably in 1975, and in walks our famous professor, Dr. Cronin. I remember he was wearing hiking boots and looked very fit. The first thing he said to us: ''I don't know anything about solid state so we will learn this together'' and so we did.

Mario Pimenta
LIP/IST; Colleague
September 10, 2016
Faro, Portugal - September 2007 - first photo
Jim visited Faro, Portugal in September 2007 to lecture in the “New Worlds in Astroparticle Physics” workshop. He gave a lively lecture on the conception, building and first results of Auger, as well as an evening public session, which was attended by many high schools students. I do remember how students were amazed to discover a Nobel Prize winner that was a charming human being able to explain that he had no answer to many questions.

These photos were taken at that time at Ilha Deserta, near Faro. It was a very pleasant “session” at the beach followed by a nice fish lunch. Jim was very happy to swim on the “European” Atlantic Ocean and I keep as a memory and an example his deep and joyful regard on all the details of life.

Faro, Portugal, September 2007 - lunch at the beachFaro, Portugal, September 2007 - Jim and Carol 

Duncan Carlsmith
Former student
September 10, 2016
Beginning in 1979, as a University of Chicago graduate student in physics, I worked with Jim Cronin and Bruce Winstein (my advisor) on Fermilab experiment E617, a precision measurement of the CP-violation parameter epsilon' in the neutral kaon system. Jim was responsible for designing and constructing open low mass 4-layer drift chambers for the magnetic spectrometer and supervised graduate student David Coupal. Bruce was responsible for designing and constructing a lead glass electromagnetic calorimeter and supervised myself, Robert Bernstein, and Hamish Norton. The detectors were fabricated in the Enrico Fermi Institute. Saclay physicists joined us in operating the experiment.

Jim was the de facto lead of the high energy group at Univeristy of Chicago. He was to students a profoundly important educator and role model. He would personally corral us from our offices to weekly group meetings, be attentive to our required presentations, and escort us to weekly departmental colloquia and Institute seminars, emphasizing the importance of an interest in all things. Generally serene and personable, he joined us in outings to Greektown for a Friday night social gathering. He taught me in a graduate lab class to appreciate Mossbauer spectroscopy, atomic resonances, and other phenomena unrelated to high energy physics, as well as the phenomenology of the kaon system. Only much later did I appreciate the difficulty of obtaining and maintaining a Fe source for Mossbauer spectroscopy in an educational environment.

Of the many memories I have of Jim and of his influence upon me during this formative period in my life, I'll share just a few anecdotes as best I can remember.

Jim and David carefully and repeatedly measured the location of the kaon production target, drift chambers and calorimeter along the E617 beam line with a long tape measure. I think Robert and I were having trouble making sense of the data and simulation comparison. We were running Fortran code on a then cutting-edge Harris computer, fed with punch card decks. It turned out the problem was that the tape measure was in metric inches, 10 ''inches''/ft as I recall, though perhaps my leg was being pulled. I learned from Jim's characteristically humble and bemused discovery of the error that a revered Nobel Prize winner was, like the rest of us, subject to human error.

I remember too an encounter while I was feeling frustrated working alone in the operation of re-gluing some large number of phototubes, each to an expensive lead glass block. After a long operation of ''potting'' cylindrical mu-metal magnetic shields to the ends of the blocks, and optically coupling and sealing the PMTs in place within the shields, the whole collection had been moved to Fermilab in the dead of winter. Freezing temperatures in the meson beam line and differential expansion resulted in many of the magnetic shields shearing off, taking shards of glass with them, damaging the ends of the blocks, but luckily not the phototubes. We faced a crunch to disassembly, fix each element back on campus, design and build a thermally stable environment to house the calorimeter in the beam line, and reassemble and re-test everything before our scheduled spring beam time. Working away on my cleaning and gluing task in the cold at the Institute, and wondering if we would have another uncontrollable temperature excursion there and then or get it all done and out to a thermally controlled environment at the lab safely, I grumbled as Jim passed through the work space. He sat right down and helped me with the work. I immediately regretted having been churlish.

Jim won the Nobel Prize in 1980. I recall Jim and I both attended a lecture class in general relativity taught by with Subrahmanyan Chandrasekhar who arrived each day in his signature dark suit with white kerchief in the breast pocket. A grade of 'B' was to be awarded for perfect attendance. The only other available outcome would be a 'F' or the equivalent, Jim's attending a class along side the graduate students appeared to me a testament to his humility and deep love of physics. Of course, he was attending as a role model for graduate students also. Chandra presented some mathematics of curved space-time of his own devising and, a few weeks in, threw in scalar and spinors fields. I could not keep up and I believed Jim too struggled, but we stuck it out. I might not have had not Jim been there too. I believe Jim received the announcement of his Nobel Prize award during that class. Chandra was awarded the Nobel Prize a few years later.

Jim was initially skeptical of my particular PhD thesis project, a project suggested by Bruce and something of an independent effort using the E617 set up and requiring two weeks of precious beam time, even after I showed him calculations and simulations. When the measurements were complete and physical effects found as anticipated, I was especially proud to show the results to Jim and to earn I thought some measure of his respect. He was already involved in a new experiment at CERN with I think David by then, a clever first direct measurement of the neutral pion lifetime using pair conversions in thin-foil stack.