Caltech Partners with Local High Schools to Measure Subatomic Shrapnel

PASADENA, Calif. – They stream out of deep space, traveling at speeds
close to that of light, constantly bombarding Earth and literally
passing through our bodies: subatomic shrapnel, as one magazine
described them, energetic bits of matter known as cosmic rays.

For the past year, Los Angeles-area high school students and their
teachers have teamed up with a Caltech physicist to, in a sense,
“catch” these ultrahigh-energy rays on their own campuses. Students
and their science teachers from the Pasadena Unified School District,
Los Angeles Unified School District, and other districts in Southern
California, have been involved in the development and construction of
detector hardware, the associated electronics, and the computer
equipment to form a networked system among 30 Southern California
high schools. The project is called the California High School
Cosmic-Ray Observatory (CHICOS). Ultimately, says Caltech physics
professor Robert McKeown, at least 90 detectors will be installed,
scattered widely throughout Southern California.

A large array of detectors will enable the study of these
ultrahigh-energy cosmic rays through the detection of “showers,”
several kilometers in radius, of secondary particles they create in
the Earth’s atmosphere. Such rays are the highest-energy particles
ever observed in nature and have captured the fancy of the
astrophysics and particle-physics community. Thus, while establishing
a state-of-the-art experimental facility, the project is also
providing an exceptional educational experience for local high school
students. When a majority of the sites are operating, McKeown expects
the project will yield enough significant science to be reported in
the scientific journals.

Cosmic rays are comprised of protons, neutrinos (uncharged elementary
particles), gamma ray photons (bits of light emitted spontaneously by
a radioactive substance), and other subatomic “stuff.” They are of
interest to scientists for a couple of reasons. For one, studying
their composition tells how the galaxy has continued to evolve
chemically since the solar system was formed. This helps us to
understand how the solar system got the chemical composition that it
has, and, in turn, tells us something about our origin. Further, as
energetic as they are, cosmic rays may emanate from cataclysms of
staggering proportions, including the Big Bang, shock waves from
supernovas collapsing into black holes, and matter that’s accelerated
as it is sucked into massive black holes. Knowing where these
particles originate and how they attain such colossal energies will
help scientists understand how these violent objects operate.

“The idea is, ‘what do these things point back to?’ ” says McKeown.
“And, can we learn something about where they come from as a result
of that? This is real science. Maybe these things will point back to
some exploding object in the sky, which is exciting to kids. And to
me, for that matter.”

The timing of when the showers hit the different schools is what
tells scientists like McKeown a lot about where they came from. The
cosmic rays will generate a “pancake” of rays that, as it falls, gets
bigger and bigger. The particles will hit one detector first, then
another one sometime later. The detectors at the center of the shower
will have stronger signals than the detectors farther away.

Once the center of the shower is detected, the direction of the
shower can be determined from the relative times. This is where the
high school kids come in–using trigonometry, they can reconstruct
the direction of the showers, taking into account the orientation of
the earth at that time.

The program also incorporates a high-school-teacher education
component coordinated by Dr. Ryoichi Seki at California State
University, Northridge. Teachers are developing curriculum materials
to help their students participate in this research. Caltech also
hosts a summer workshop where physics teachers and students can
participate in the construction of new detector stations for
deployment at additional sites.

“One of the things I like to show the students and teachers is that
this really is a current and ongoing research project,” says McKeown,
“so it’s not an exercise out of a textbook but real science.”

For more information on CHICOS, please see http://www.chicos.caltech.edu/.