Prize Press Conference for Raymond Davis, Jr., October 8, 2002
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.
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.
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.
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,
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.
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
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!
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.
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.
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.
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.
Preston, SAS Dean
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
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
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.
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
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
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
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.
of those scientists are with us here today, all of them members
of our Department of Physics and Astronomy:
Lande, who worked with Davis on the Homestake Experiment and served
as director of the project for over a decade,
Beier, who most recently has served as U.S. principal investigator
for the Sudbury Neutrino Observatory,
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,
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
Nobel Prize announced today is an honor not only for Ray Davis but
for his entire department, and we are very gratified.
Lubensky, Chair, Dept. of Physics
role is mostly to introduce Ken Lande who will share some of his
experiences with Ray. Ken mostly collaborated with Ray while he
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.
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.
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.
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
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.
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.
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.
article, "Nobel Prize in Physics: Raymond Davis, Jr."
Almanac, Vol. 49, No. 8, October 15, 2002