Experimental Particle Astrophysics

Utah is rapidly becoming established as one of the world's centers for high energy astrophysics research. Over the last decade, the cosmic ray group (Loh, Sokolsky, Salamon, Kieda, Tang, Elbert, Sommers, Corbato) has built and operated the "Fly's Eye" observatory. Located in the Utah desert, this large detector measures the most energetic particles in the Universe, ultra-high energy cosmic rays. Measurement of the energy spectrum, composition, and arrival directions of these particles, whose energies extend to 1011 GeV, provide crucial information on the most powerful astrophysical acceleration processes that occur in the cosmos. These processes possibly include particle acceleration at the accretion shocks of quasars and other active galactic nuclei, in the jets of radio-loud galaxies, in the stellar winds of highly massive stars, in the termination shock of the galactic wind of the Milky Way, and in compact objects (neutron stars, black holes) within our Galaxy.

The cosmic ray group, in collaboration with Columbia University and the University of Illinois, is currently building a second generation instrument, the "High Resolution Eye," whose event resolution will be unmatched by any other present or planned ultra-high energy cosmic ray detector. A recent National Research Council Report on physics in this area notes that "the Fly's Eye program is unique among experiments around the world for studying cascades [i.e., extensive air showers that are produced in the Earth's atmosphere by the incident cosmic rays] of 1018 eV and higher energies, and it serves as a focus for cosmic-ray research at the highest energies in the United States." In the last few years we have been joined by the University of Chicago, the University of Michigan, and the University of Adelaide in Australia, who have established large-area surface and underground arrays for the joint detection of these energetic particles at the Fly's Eye site.

There is an active intitiative to make the University's cosmic ray research relevant and accessible to school students in the State of Utah. Department researchers are working with primary and secondary school science teachers to develop lessons to be available via the World Wide Web. The home page for this project is called Cosmic Web.

Research is also being conducted on lower-energy cosmic rays. Two of our faculty (Salamon, DeFord) recently returned from the Antarctic, where they flew a balloon-borne magnetic spectrometer to measure the isotopic abundances of the iron-group cosmic ray nuclei. These studies will provide information on the life history of nuclear cosmic rays, and on the processes of stellar nucleosynthesis that occur at the end stage of a star's life, just before and during the supernova phase.

Because our astrophysics research program is growing both internally and through national and international collaborations, the department and University established the Astrophysics Institute of the University of Utah. This institute provides support for visiting scholars and collaborators, and serves as a center where high-energy astrophysicists from around the world can meet to exchange ideas and work together. It will also be the site of an annual international workshop on current topics of interest in high energy astrophysics, both in experiment and theory.