The Telescope in the Ice

by Mark Bowen

  He had driven south from Geneva with his wife, Nelly, and they were planning to drive back the minute his talk was over. She was waiting outside in the “ugly hippie yellow/orange (excuse: we had no choice, we took the first model available)” MGB sports car that Francis had bought with a portion of the prize money he had won for his Ph.D. thesis at Leuven, two years earlier.

  On his way out of the hotel, he was told that someone wanted to speak to him. “They better be important and be fast,” he responded, “because my wife is waiting in the car.”

  The someone turned out to be Vernon Barger, the theorist who had hosted Francis’s co-author in Madison. Barger explained that he didn’t have a job to offer, but that he could probably find a way to support Francis for a visit of about six months.

  “I was a bit of a dilettante at the time—probably still am,” Francis observes. “I am not driven by plans or ambition.… I do what I want to do; you only live once.… This was better than going back to Belgium that particular day, so I go.… I mean what can go wrong in six months?” There wasn’t much risk involved, since he had the job lined up in Belgium.

  His visit began on October 6, 1971. (“Immigration made sure that I never forgot that day.”) Almost half a century later, he’s still there.

  * * *

  Another of Dave Cline’s contributions to “Wisconsin-style physics” was to observe no clear boundary between theory and experiment. He often collaborated with Vernon Barger. The two had become “semi-famous,” he recalled, by demonstrating that a new theory of so-called Regge Poles fit some new accelerator data—and they had also become infamous when Cline had once snapped a picture of a slide at a conference somewhere, brought it back to Barger to analyze, and the two published the correct interpretation of the data on the slide before the group that produced it did.

  Dave had been toying with the idea of starting a “phenomenology” group to work at the interface of theory and experiment. When Francis arrived, Dave recognized his cleverness and broad knowledge right away and realized that Francis “fit perfectly into this picture.” Dave was the principal investigator (PI) of the E1A experiment at that point, so he was bringing in roughly $1.5 million a year. When the money that Barger had found for Francis ran out, Cline hired him as a post-doc on the E1A project—a pure theorist working on an experiment, unheard of at the time—and made him an offer of a permanent position in the non-existent phenomenology group that he had in mind.

  Cline was virtually unstoppable in those days. The phenomenology group was born in a meeting with the dean of the Madison graduate school and Cline’s grant manager at the Department of Energy, when the dean promised $1 million from a remarkable fund at the University of Wisconsin called the Wisconsin Alumni Research Fund or WARF (about which more later), and the grant manager offered to match it. The group consisted of two experimentalists, Cline and Don Reeder, and three theorists: Barger, another professor named Martin Olsson, and Halzen, who observes that Cline was “by far the most imaginative of us. I mean, he led in every respect.” Cline’s insight about phenomenology turned out to be right on target. It was soon recognized as a legitimate occupation.

  Cline was a synthesizer. Bob Morse says “he saw all things as being doable.” He also disregarded the border between accelerator and cosmic ray physics. “Didn’t matter,” says Bob with a laugh. “Dave said, ‘I’m interested in a particle of a certain energy.’ If it meant he had to go to cosmic rays to find them, he’d go to cosmic rays.… He didn’t see any boundaries.”

  The two most influential papers that Francis wrote during his first few years in Madison were co-written with Cline, and one of them dealt with cosmic rays—the first time Francis ventured into the field in which he would do his most important life’s work. That paper, incidentally, is also considered one of the most influential of Cline’s illustrious career. Francis recognizes Cline as one of the three or four important mentors in his life. In fact, he named his son, David, after Cline and another mentor, David Speiser, one of his advisers in graduate school.

  * * *

  And so, CCFMR trained its protean anarchy on experiments at accelerators and high-energy cosmic ray stations all over the world—usually a handful at a time. But the cosmic ray work took place mostly on mountaintops, so John Learned’s thesis research was relegated to the background. After his stint in Colorado, he worked for a few years on traditional high-energy experiments at the Argonne and Stanford Linear accelerators, while his freewheeling mentors gave him “a good deal of freedom to padiddle around” in the nascent field of neutrino astronomy. Meanwhile, Francis Halzen remained pure, merrily writing papers as theorists will, and learning something about experimentalism by way of phenomenology, but not sullying himself on any true experiments quite yet. It would be almost twenty years before AMANDA would draw his first blood.

  5. Peaceful Exploration by Interested Scientists Throughout the World

  John Learned finally found an opening in 1973, when he joined several scientists from the United States, the Soviet Union, and Japan in an informal discussion of Cherenkov detection at the biennial International Cosmic Ray Conference, which was held in Denver that year. Fred Reines was there. The Soviets were represented by Georgii Zatsepin, a brilliant experimentalist and theorist (not as unusual in Russia as it was in the west). Zatsepin had begun his scientific career in the high Pamir in the 1940s and conceived of Cherenkov-based neutrino astronomy at about the same time as Greisen and Markov, but had not gone to the trouble of writing it down. Saburo Miyake, a respected cosmic ray and neutrino specialist who had collaborated on the Kolar Gold Fields experiment, represented Japan.

  The meeting consisted of “just a few people sitting around saying we should start to take this seriously and do something,” Learned recalls. Reines coined the name DUMAND, for Deep Underwater Muon And Neutrino Detector, although the details of any such instrument were entirely nebulous at the time, and an ad hoc committee was formed. The first formal DUMAND workshop was convened at Western Washington State College in Bellingham in July 1975.

  A diverse array of experts was invited to the Bellingham workshop, including oceanographers, ocean engineers, submarine cable specialists, and biologists who might illuminate the physical scientists as to the potential effect of deep-sea life on their experiment. “For all we knew, a giant squid would try to have sex with the thing,” says Learned, not entirely in jest.

  While there is no, ahem, hard data on that particular possibility, it is well-known that many sea creatures give off light in a process known as bioluminescence, a complication well worth investigating, as it will create a disruptive background in a Cherenkov detector. At a subsequent DUMAND workshop, a specialist in marine invertebrates discussed the problem in a paper entitled “Serpents in an Astrophysical Eden.”

  * * *

  Fred Reines and John Learned were voted chair and vice-chair of a formal DUMAND steering committee at the Bellingham workshop, and Reines then went about inviting others to join, including Dave Cline, who believed he was brought in for the knowledge of neutrinos he was gaining in the E1A experiment. Dave’s CCFMR colleagues Ugo Camerini and Bob March could hardly keep themselves away from such a crazy idea, so Wisconsin became one of the principal institutions in the DUMAND collaboration.

  Reines also brought in Arthur Roberts, who was John Learned’s “grandfather” in a sense, since he had been thesis adviser to Learned’s adviser, Howard Davis. This foray into cosmic ray physics would be the coda to Roberts’s long and distinguished career. His quirky “personal history” of DUMAND would be his last academic paper. Like Reines, he had faced a career choice between physics and music in his youth—in his case piano—and all through his career, he wrote satirical songs in the vein of Tom Lehrer about physics and the academic life. One of the great benefits of having him around was that he knew about as many Gilbert and Sullivan songs as Reines did, so they would often break out in song together.

  Another physicist who fit in handsomely
was David Schramm, a renowned particle physicist-cum-cosmologist at the University of Chicago, who is said to have approached science in the same way that he approached his favorite sport, wrestling. Schramm was red-haired, six-foot-four, and had once nearly qualified for the Olympics. For many years, until his knees gave out, he kept fit by wrestling members of the Chicago Bears football team. Story has it that when he was advised as a graduate student that his thesis topic might be too chancy and contentious, he responded with an exposition of “jugular science.”

  Realizing that ocean engineering would make or break the project, Reines recruited Howard Blood, director of the Naval Ocean Systems Center in San Diego, to the cause. This was also a strategic move, since Blood’s center had a branch in Hawaii, and when the ocean experts in Bellingham had been charged with finding a site three miles deep where the water was clear and advanced facilities were located on a nearby shore, they had recommended two sites in the Hawaiian Islands.

  One of the stranger individuals to attach himself to DUMAND was a certain Peter Kotzer. He directed the Bellingham workshop and edited its proceedings. Learned is convinced that he worked for the CIA. Whether or not this is true, he was working quite openly on military applications. In fact, to give some idea of how all-seeing the military could be in those Cold War days, he had already been working for about three years on a project called UNCLE (Undersea Cosmic Lepton Experiment), in collaboration with Fermilab and the Naval Research Laboratory in Washington, D.C.

  This was the era of the reassuring nuclear deterrence strategy known as mutual assured destruction or MAD. The Soviets and the Americans had reached nuclear parity, in which it was assumed that neither side could obliterate the other without being annihilated in return, and the final ace in the hole was the nuclear-powered submarine, armed with intercontinental ballistic missiles carrying nuclear warheads. The notion was that even if one side managed to destroy all the land or air-based nuclear weapons on the other, the submarines could still rise to the surface, wherever they might be, and retaliate—if they could be reached in time. Thus both sides were working on the difficult problem of communicating with distant submarines lurking at depth.

  UNCLE was a feasibility study for communicating with the subs with neutrinos. The idea, believe it or not, was to outfit a submarine with a Cherenkov detector and use a particle accelerator to send pulses of neutrinos to it, in Morse code presumably. The great advantage of neutrinos, of course, is that they will penetrate anything, so the pulses could be aimed directly at the sub, no matter where in the oceans it might be. The usual sort of radio communication won’t work, because the usual radio frequencies can’t penetrate earth or water; only very low frequencies will, and this requires very long antennae, buried underground. (The military was working on that technology, too.)

  This strange business was a bit of a growth industry in the sixties and seventies. Even Clyde Cowan, Fred Reines’s early collaborator, seems to have been involved. He had moved from Los Alamos to The Catholic University of America in Washington, D.C., where he often collaborated with scientists from the Naval Research Laboratory, several of whom published a paper on “telecommunication with neutrino beams” in Science in 1977. According to Christian Spiering, who would later lead the German contingent in AMANDA and IceCube, the Soviets were interested, too. The notion never went anywhere, because the subs would have had to sprout enormous and ungainly wings of light detectors in order to receive the signal.

  To their credit, the decision makers in the U.S. Navy dismissed this notion out of hand. Dave Cline remembers going to a meeting in Washington to discuss funding for DUMAND with “the biggest shot admiral in the Navy.” He had taken his seat next to the admiral and Fred Reines was just walking in, when the admiral turned to his assistant and said, “I hope this isn’t like the goddamn Kotzer thing,” referring to Kotzer’s UNCLE idea. (The Navy wasn’t much interested in DUMAND, incidentally, because it was much too deep. Submarines only go down about eight hundred feet.)

  * * *

  It is hard to overstate the significance of DUMAND. At first, everything about it was as big and bold as Dave Schramm. For the first five years, it survived on the motherly love of a small group of pioneers. Arthur Roberts was the only full-time contributor, thanks to the support of Robert Wilson, the Wyoming cowboy who ran Fermilab, while the rest supported themselves with other grants, such as E1A, and nurtured the project along in their spare time. Although the name was later attached to a specific instrument, DUMAND was, and still is, basically a concept, encompassing underwater and underground neutrino astronomy in all its forms. It is fair to say that nearly every advance that has been made in neutrino astronomy over the past four decades was prefigured in some way by this collaboration. They even considered ice, but rejected it on the grounds that the logistics would be insurmountable in the polar regions, which are the only places on Earth with ice sheets thick enough to provide the requisite shielding from cosmic rays. These many years later, those few IceCube scientists who are even aware of DUMAND still appreciate the debt they owe to it. Bob Morse points out that you can tell how much influence DUMAND had by the fact that AMANDA even copied some of its mistakes!

  Arthur Roberts presented their first thoughts at an international neutrino conference in Aachen, Germany, in June 1976. They had come up with three fundamental concepts and endowed them with mythological names: UNDINE (UNderwater Detection of Interstellar Neutrino Emission), ATHENE (ATmospheric High Energy Neutrino Experiment), and UNICORN (UNderwater Interstellar Cosmic-Ray Neutrinos).

  One of their first insights was to realize that neutrinos with different energies called for different instruments and that higher energies called for larger instruments. This followed from the fact that low-energy muons travel a shorter distance in the detection medium than high-energy muons will, and give off less light altogether, since they have less energy to expend on that light in the first place. The size of a cascade induced by an electron neutrino will scale with energy as well.

  UNDINE, the smallest of the three concepts, was aimed at detecting low-energy neutrinos, in the range from a few million to about a hundred million electron-volts, emitted by the Sun and nearby supernovae—the latter being much more interesting, but exceedingly rare. It is believed that a supernova takes place in our galaxy, the Milky Way, just once every fifty years on average, but that most go unseen by optical telescopes as they are obscured by interstellar dust. This is no problem for a neutrino detector, of course, since neutrinos pass through dust as if it isn’t there, but fifty years is longer than the lifetime of most scientific instruments—not to mention the careers of most scientists—so the case for UNDINE was not compelling. The scientists estimated that they could observe a supernova about once a week if they extended their reach to the nearest cluster of galaxies, the Virgo Cluster, but that that would require a detector weighing 100 million tons, which seemed out of the question.

  ATHENE and UNICORN were aimed at high-energy neutrinos, with energies above a billion or a trillion electron-volts. ATHENE would focus on atmospheric neutrinos, while UNICORN was aimed at the most exciting scientific frontier: cosmic particle accelerators in deep space. In other words, it was actually a telescope. The only real difference between these two concepts was their size. UNICORN was larger and therefore more sensitive, and this was the concept that would evolve into DUMAND the instrument, AMANDA, and IceCube.

  The DUMAND pioneers realized the magnitude of the challenge from the outset: in order to see objects outside our galaxy, they calculated, UNICORN would need to comprise at least a cubic kilometer of water. But the idea was exciting, nevertheless. “Adherents began to gather.”

  * * *

  What is now seen as the seminal meeting in the field of neutrino astronomy took place in Honolulu in September 1976, when scientists from the United States, Japan, Switzerland, Germany, and Russia converged for a summer workshop hosted by the University of Hawaii.

  The three mythological concepts wer
e refined. UNDINE, the low-energy concept, solidified into a design in the Greisen style: a shell of tightly packed light detectors enclosing a tank of water. The standard detector for ultra-sensitive light detection is the photomultiplier tube or “phototube,” which can detect even a single photon under the right conditions. But these are expensive items, roughly $3,000 apiece with their associated electronics, so a large shell-type instrument can be rather expensive to build. One of the current realizations of UNDINE, for example, is Super-K, the Super-Kamiokande detector, situated deep in a zinc mine in the Japanese Alps. Super-K contains “only” about 50,000 tons of purified water, so it’s 20,000 times too small to detect a supernova in the Virgo Cluster, yet it still takes 13,000 phototubes to cover the walls of the tank. That’s $40 million for the tubes alone. A simple scaling argument shows that if you wanted to make a shell-type instrument capable of seeing into the Virgo Cluster—weighing 100 million tons, that is—you would need about 2 million phototubes, which would cost about $6 billion.

  ATHENE and UNICORN manifested as plum pudding designs in the Markov mode, in which the detection volume is filled with a grid of phototubes. Since this design requires fewer detectors per unit volume, it is less expensive than the Greisen variety. It also has better resolving power, so it’s more suited to a telescope.

  Since UNDINE would have had to have been prohibitively large in order to have a reasonable chance of detecting a supernova before the conferees died, she was rejected at the Hawaii workshop. Arthur Roberts writes that “UNDINE was returned to her sunless and solitary abode, there to be wooed and won by other suitors.” The winning would not take long, and the union would prove remarkably fruitful.