An essay on why I am a Neutrino Physicist,
written for a book of portraits of
scientists by Mariana Cooke, in publication
You can't see them but they're everywhere. There are 60 billion in
front of your nose this second. You can't smell them. You can't taste
them when they touch your tongue. You can't hear them. You can't feel
them when they pass through you. 10,000,000,000,000,000 will do it
while you read this page and you will never know.
They are neutrinos, the ``little neutral ones'' in the family of
subatomic particles. Neutrinos hold secrets from the
earliest days of the universe. They bring us information from deep
inside exploding stars and from high energy particle collisions. Their
presence may signal unexpected phenomena. Measuring their properties
will help us understand how the universe will evolve.
We search for neutrinos using detectors all around the world. My
experiment is at Fermi National Accelerator Laboratory, located just
outside of Chicago. Our detector, MiniBooNE, is a forty foot high sphere,
filled with mineral oil. When the neutrinos interact in the oil,
they make small flashes of light which are seen by phototubes, which
work essentially like inverse light bulbs: light goes in, an electrical pulse
comes out. The phototubes are 8-inch diameter circles that are beautiful
dark amber. When we installed them on the ceiling of the detector,
MiniBooNE looked like a bizarre, beautiful planetarium with many moons
and tiny stars that were the screws holding the tubes onto their black
support structure. Despite being made of 800 tons of oil, MiniBooNE is
actually quite mini compared to other neutrino experiments. The most
awesomely large neutrino detector, Super-K, is located in Japan.
A fifteen story building can fit comfortably within that detector!
We need such large detectors because neutrinos don't interact with
matter very often. Most subatomic particles are very interactive. For example,
quarks, which make up most of ordinary matter, are so active in our
detectors that it is difficult to sort out the patterns that they
leave. The electron is another highly evident particle -- and
reliable, too. You can count on finding electrons inside your typical
wall outlet and also inside your typical particle interaction. But the
neutrino is different from the rest. Their interactions occur far
more rarely. At the highest energy accelerator in the world, Fermilab,
we observe neutrino reactions 10,000,000,000 times less often than
those of quarks. They just quietly zip through the detector and go on
their merry way.
Neutrino research is fascinating today because the results are full of
contradictions. For fifty years, all of the evidence pointed to
neutrinos being bundles of moving energy that had no mass -- a pretty
weird concept for a particle. But recently we discovered a novel
behavior which can only be explained if neutrinos do have mass.
How do resolve this conflict?
If the neutrino has mass, it must be very, very small. It would take
at least half a million neutrinos to tip the scales on the
electron. Still, such a wispy particle will have a big effect in the
universe. The collective mass of the neutrinos rivals the mass of all
the stars! Given the discovery of mass, we can begin asking even more
exciting questions. The Big Bang, for example, produced a million
neutrinos in every gallon of space. The holy grail of neutrino physics
is to detect these relics. Their mass may hold the key.
All of that sounds pretty esoteric, and you may ask: ``What have
neutrinos done for me lately?'' Actually, they matter a lot to you.
They are part of the ignition process of the sun. They play a role in
heating the center of the earth, causing continental drift. So the
next time you see a koala, whose evolution depended on living on an
isolated continent, thank a neutrino! The tools that physicists use
to create and study neutrinos have direct benefit to every one of
us. One fork of the beam line for our neutrino experiment at the
Fermilab goes to Neutron Therapy, a very successful cancer treatment
method. The extremely clean laboratory environment of state-of-the-art
solar neutrino experiments can be used for sensitive tests to monitor
violations of the nuclear test ban treaty.
I love this particle because it always reminds me that even the
smallest among us can change the universe.