Knowing the direction from which a particle arrives is critical because a downward trajectory indicates that it is from outside Earth's atmosphere. As many as 15 million particles trigger the detector in a 24-hour period, but many are false alarms from various sources, according to Dr. Nutter, who is working with scientists from the University of Chicago, The University of Michigan, Penn State University and Indiana University. The HEAT-PBAR allows scientists to determine what kinds of cosmic rays are traveling through the galaxy. Cosmic rays are primarily protons, the nucleus of a hydrogen atom which is the most abundant element in the universe. This particular experiment will concentrate on detecting protons and antiprotons, or antimatter.
Protons give the nucleus of atoms their charge and are one of the basic building blocks of atoms.
But cosmic rays represent the only sample of matter from beyond our solar system we have available. By analyzing the composition of these particles which were accelerated from interstellar material only about nine million years ago, we are learning a tremendous amount about the way our galaxy has evolved chemically since the solar system's formation. Every time a cosmic ray hits the walls of the box, it has a chance of leaking out, escaping the galaxy. This leaking changes what eventually reaches Earth. Scientists must understand how to compensate for the leaking in order to know the composition of the galactic matter that is the source of cosmic rays.