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Nobel Prize Press Conference for Raymond Davis, Jr., October 8, 2002

Robert Barchi

As Provost, it's my privilege to welcome the members of the press here on behalf of our President, Judith Rodin and the entire Penn community.

We want to thank you for joining us for this extraordinary occasion to celebrate the awarding of the Nobel Prize in physics to one of our most distinguished scientists--Raymond Davis.

As President Rodin has said, "This is a great moment for an extraordinary researcher, for the University of Pennsylvania and for the world of science." You can almost feel the buzz of energy on campus when this most prestigious of scientific honors is bestowed on one of our own.

Dr. Davis, research professor of physics at Penn since 1985 and research collaborator in chemistry at the Brookhaven Lab in Upton, New York, shares the honor with Masa-toshi Koshiba, of the University of Tokyo and Riccardo Giaconne of Associated Universities, Inc. in Washington, D.C.

Professor Davis' groundbreaking work has given rise to the discipline of neutrino astrophysics, a field that has already told us much about our own sun and other astronomical objects and may yield equally stunning insights in to the nature of matter itself.

Professor Davis first detected solar neutrinos in 1967, when he observed the neutrino-induced conversion of chlorine atoms into argon atoms in a 615-ton neutrino-detector lab built one mile deep in an abandoned gold mine at Lead, South Dakota. The subterranean location served to screen out cosmic radiation and other contaminating background noise, while neutrinos passed easily through the 5000 feet of rock and earth to reach the detector, a 100,000-gallon tank filled with perchloroethylene.

Using this elegant but arduous approach, Professor Davis and his colleagues first confirmed the existence of solar neutrinos, proving that the source of the sun's energy came from nuclear fusion reactions deep in its core. Surprisingly, however, the number of neutrinos reaching the earth was just one-third of that predicted by detailed models of these nuclear reactions within the sun. In this experiment and subsequent ones in Japan and Canada, Dr. Davis and his colleagues discovered that some electron neutrinos produced in solar fusion reactions convert into other neutrino species -- muon and tau neutrinos -- during the eight-minute journey from the solar core to the Earth. These experiments also demonstrated that neutrinos have a very small but measurable mass; because of the enormous number of neutrinos in the universe, scientists now think that their combined mass may be equivalent to the total mass of all the visible matter in the universe. It is not an overstatement to say that this detection of a previously unknown class of particle interactions may ultimately help us to better understand the very evolution of the universe!

Ray Davis is a truly outstanding scientist and an inspiration to us all. Earlier this year he received the 2001 National Medal of Science. He is also a member of the National Academy of Sciences and the American Academy of Arts and Sciences.

We are extremely proud of him and his colleagues and offer our heartfelt congratulations to him and to the other Penn scientists who have collaborated with him over the years, many of whom are here with us today. You'll be hearing from one of them, Professor Ken Lande.

I'd like to also commend the Physics Department, the School of Arts and Sciences, and of course the broader University, for this remarkable achievement. You have made all of us very proud to be at Penn.

Now I'd like to invite Sam Preston, Dean of SAS, to the podium. Sam would like to share a few words about Professor Davis and the significance of this award for both Ray Davis and for Penn.

Sam Preston, SAS Dean

This is a very exciting day for the University and for the School of Arts and Sciences. Today's announcement is a wonderful tribute to the entire Penn scientific community, and marks the second time in three years that a Penn scientist has won the Nobel Prize. Alan MacDiarmid of our Chemistry department won the Chemistry Nobel in 2000.

Ray Davis has long been acknowledged by the international scientific community as a pioneer in the study of neutrinos and it is enormously gratifying to see him achieve this pinnacle of recognition for his work.

As the Provost noted, Ray joined the Penn faculty in 1985. His initial appointment here was in what was then known as the Department of Astronomy, since his research focused on the behavior of the sun.

But Davis's work is a wonderful illustration of the unity of science: observations of radiation from the sun, made in the depths of a goldmine, tell us something of fundamental importance about elementary particle physics.

The fact that astronomical observations are a growing source of fruitful insight into fundamental physics is the principal reason why our physics faculty decided seven years ago to combine with the Department of Astronomy and subsequently to make astrophysics its most prominent growth area.

Ray Davis epitomizes the spirit of scientific observation and discovery. As Bob noted, the number of solar neutrinos that he measured as reaching the earth were was one-third that which previous theory had predicted.

This was the first evidence of the so-called "solar neutrino problem," the solution of which required a world-wide effort that included important contributions from many members of the Penn family.

Several of those scientists are with us here today, all of them members of our Department of Physics and Astronomy:

Ken Lande, who worked with Davis on the Homestake Experiment and served as director of the project for over a decade,

Gene Beier, who most recently has served as U.S. principal investigator for the Sudbury Neutrino Observatory,

Alfred Mann, who was a pioneer in applying the large-scale techniques of accelerator-based elementary particle physics to the new field of underground observations of laboratory astrophysics,

and Paul Langacker, former chair of the department, who has played a major role in advancing understanding of the relationship between theoretical calculations and experimental observations in neutrino physics.

The Nobel Prize announced today is an honor not only for Ray Davis but for his entire department, and we are very gratified.

Tom Lubensky, Chair, Dept. of Physics

My role is mostly to introduce Ken Lande who will share some of his experiences with Ray. Ken mostly collaborated with Ray while he was here.

I do want say a few words about neutrino physics and the physics department. We have had ongoing and strong leading programs in neutrino physics for over 30 years. We've had accelerator-based experiments we were a major player in the Japan experiments that saw not only solar neutrinos but neutrinos for super nova. We are part of the SNO (Sudbury Neutrino Observatory) Project. We are really one of the leading institutions for neutrino physics, which is really one of the most difficult types of physics to do. You will hear Ken tell you about how they detected individual atoms whose nature was changed by the passage of a neutrino. That's something you don't often hear about because they interact so weakly.

Kenneth Lande, professor of physics

I would like to tell you a little bit about the experiment, but more importantly, I would like to tell you about Ray Davis. Ray is extraordinary person, a fantastic scientist and a wonderful friend. I worked closely with him for many years and over that entire period, it was always a tremendous pleasure to go to the lab every morning, to see Ray, to work with him, to talk with him, to know him. He is imaginative and creates excitement about everything that goes on around him. He was extremely supportive to our students and an ideal role model. And as you can see, he's also very persistent at getting to the answer. Few others would have spent 37 years studying the emission of neutrinos from the sun. We are all fortunate that he did since we now have a much clearer understanding of how the most important object in our lives, the Sun, generates energy.

Since the neutrinos from the sun convert one chlorine atom into an argon atom in the detector every two days, the scientific challenge was simple, find and remove about 15 atoms per month from 615 tons of detector material. Even today the task seems overwhelming, but Ray did it and did it with great precision. He measured the flux of solar neutrinos to a statistical precision of about 5%. It is hard to imagine how much more difficult that task must have appeared in 1965, when Davis began the experiment.

As Provost Barchi pointed out, the detector itself must be located deep underground to avoid confusing backgrounds from cosmic rays. Fortunately, the deepest mine in the United States, the Homestake Gold Mine in Lead, South Dakota, was willing to build a laboratory 4850 ft. below the surface of the earth. In 1965 they agreed to excavate a very large chamber, 30 ft high by 30 ft wide by 60 ft long, to house the detector as well as considerable auxiliary space for a control and sample processing room in that deep underground location. Over the past 37 years, the Homestake Mining Company constantly provided us with support and help without which it would have been impossible to carry out this experiment. This is a classic textbook example of how industrial-academic cooperation can further the frontiers of science and increase understanding of the universe in which we live.

We are very grateful to the miners, the engineers and all the others who were always there when we needed them. Lead is a small mining town in the midst of the Black Hills of South Dakota. Such towns normally do not care about neutrino astrophysics. The residents of Lead do! Lead now annually celebrates "Neutrino Day." I wonder where else that happens.

Finally, there are all the wonderful colleagues at Brookhaven and Pennsylvania with whom we worked over these many years, John Galvin, who always accompanied Ray on his trips to the mine, John Evans, who set up the first data analysis system, Bruce Cleveland, who participated in every aspect of the experiment for about two decades, Ed Fireman, Jack Ullman, and C.K. Lee, who was responsible for a broad variety of tasks. We also had some wonderful graduate students who worked with us. Among them were Jim Distel and Paul Wildenhain who, in the mid-1990s recalibrated the entire detector and counting system, reevaluated all the uncertainties, statistical and systematic, and kept the detector going. Finally, and most critically there were the program officers at both the Department of Energy and the National Science Foundation who provided the support for this work. Without the continuing support of scientists such as Morris Aizenman at the NSF, this experiment would have terminated prematurely.

Of course, this is only the beginning of neutrino probes of our universe and of the physical laws that govern its evolution. Hopefully, today's recognition of the Kamiokande and Homestake experiments as well as those at Sudbury in Canada, at Gran Sasso in Italy and at Baksan in Russia, and the amazingly precise predictions of the solar neutrino emission, the Standard Solar Model, developed by John Bahcall of the Institute of Advanced Studies at Princeton will help inspire the next generation of scientists to use neutrino astrophysics to further explore the wondrous universe in which we live.

See article, "Nobel Prize in Physics: Raymond Davis, Jr."

  Almanac, Vol. 49, No. 8, October 15, 2002