This proposal requests support for the Telescope Array (TA) operational responsibilities and activities of the Utah cosmic ray group. One of the goals of TA is to resolve the discrepancy between the measurements of the ultra high energy cosmic ray (UHECR) spectrum in the region above 5 x 10**19 eV by the HiRes and AGASA experiments. This project is a successor to both the AGASA and HiRes detectors and, as such, draws on the experience of both groups. The TA detector is a hybrid of the air fluorescence and ground array techniques used to measure the properties of UHECRs. The improved angular resolution will help in identifying possible sources and measuring anisotropies in the arrival directions of UHECRs. These data will help address the fundamental questions in astrophysics of what are the sources of the highest energy particles and how are these particles accelerated to such fantastic energies? One suspected source is Active Galactic Nuclei (AGNs) which are among the most energetic objects known in the Universe. There are tantalizing hints of correlations with BL Lac objects which are AGNs with their jets pointed towards us.
TA is located near Delta, UT. Like HiRes before it, the Utah group serves as host to the experiment and has numerous critical responsibilities in the design, integration, deployment, operation and management. After commissioning finishes later this year, TA will be the most sensitive cosmic ray detector in the Northern Hemisphere. The group plans to continue their activities in support of detector installation, commissioning, and operation and to take a leading role in the analysis of TA data, especially the fluorescence analysis.
Since 1997, the Astrophysics Science Project Integrating Research and Education (ASPIRE) has been creating some of the Web?s most engaging and interactive science lessons and labs. In addition to creating and maintaining the website, ASPIRE provides direct outreach to area teachers, students, and the public. Such efforts include providing outreach and support to local groups (especially those underrepresented in the sciences), running summer workshop sessions for students, and visits to rural schools such as Millard and Delta, UT.
NSF Award PHY-0758342 Pierre Sokolsky, Charles Jui, and John N. Matthews University of Utah, Department of Physics and Astronomy High Energy Astrophysics Institute Intellectual Merit This grant funded experimental research studying the physics of ultrahigh energy cosmic rays with two experiments located in the west desert of Utah, the High Resolution Fly’s Eye (HiRes) and Telescope Array (TA) experiments. The aim of the research is to understand what ultra high energy cosmic rays are, where they come from, and how they are accelerated. The ultra high energy regime covers approximately 1x1018 eV < E < 3x1020 eV. Ultra high energy cosmic rays are the most energetic particles in the universe, and the highest energy cosmic ray ever observed had the enormous energy of 51 Joules, the energy of a well-pitched fast ball, all concentrated in a single elementary particle. The highest energy cosmic rays are quite rare, arriving at the Earth at a rate of about one per square kilometer per century. In order to make a measurement in a reasonable amount of time, very large experiments are needed to observe these events. HiRes (which concluded in this grant period) and TA (its successor) are the largest such experiments in the northern hemisphere. There is a theoretical upper limit to the energy of a cosmic ray, called the Greisen-Zatsepin-Kuzmin cutoff, which is caused by interactions of cosmic rays with photons of the cosmic microwave background radiation. Our group and others in the HiRes experiment made the first experimental observation of the cutoff (nearly 40 years after it was first predicted). This observation has been confirmed by additional work done by our group in the TA experiment and another experiment based in Argentina. Modern cosmic ray experiments use two detector techniques: observing air shower particles using arrays of particle detectors deployed on the surface, and observing the nitrogen fluorescence light emitted as cosmic ray air showers propagate through the atmosphere. TA has both kinds of detectors, and is engaged in developing the experimental techniques necessary for better understanding the data which we collect with them. We made a major breakthrough in the analysis techniques of surface array data. All such analyses involve making a simulation of the data by the Monte Carlo technique, and until now simulating air showers has been very inaccurate due to the enormous amount of computer time necessary. The main approximation technique used, called "thinning", has been inadequate for the needs of experiments. Our group has solved this problem by inventing a technique we call "dethinning" which restores the information lost in this approximation. This has allowed us to perform an analysis of TA surface detector data that is of unprecedented accuracy. Our data is now being used to measure the spectrum of cosmic rays and to search for anisotropy in their pointing directions. See also: www.telescopearray.org/ and www.cosmic-ray.org/ Broader Impacts: In addition to improving the state of knowledge of the field of cosmic ray physics and educating postdocs, graduate and undergraduate students, the proponents of this grant worked in several outreach areas: judging local science fairs, giving talks to undergraduates on our research, giving tours of the experiment to Utah state legislators and resource managers, working on the design of the TA Visitors’ Center in Delta, Utah, and participating in the ASPIRE project of the cosmic ray group of the University of Utah. See also: http://aspire.cosmic-ray.org/
