IceCube is a neutrino observatory at the South Pole. It consists of more than 5000 digital optical modules between 1.45 and 2.45 km deep in the dark, clear ice of the Antarctic glacier. Each module includes a 10 inch photomultiplier, an onboard computer, and associated electronics, all contained inside a glass pressure sphere and connected by wires to the central data acquisition system. IceTop is the surface component of IceCube, with a pair of ice-filled tanks near the top of each down-hole cable. Each tank is instrumented with two modules integrated into the overall IceCube data acquisition system. As charged particles pass through the ice, whether deep in IceCube or in the surface tanks they generate flashes of light that are digitally recorded.
This award will provide support for the University of Delaware group to study the high-energy cosmic-ray events detected by IceCube. The novel feature of IceCube as a cosmic-ray detector is its ability to study events seen in coincidence by both IceTop and the deep detectors of IceCube. The ratio of signal in deep detectors to signal on the surface is sensitive to the relative concentration of different groups of nuclei in the primary cosmic radiation in a high energy range not accessible to direct measurements. A particular emphasis of this work is to search for a transition from galactic cosmic rays to a higher energy population of particles from extra-galactic sources. The two populations would be differentiated by their composition and energy spectra. The results will contribute to understanding the sources and acceleration mechanisms of high energy particles in Nature.
Broader Impact: Undergraduate physics students are involved in the calibration procedure and in creating processing, triggering and reconstruction algorithms. They make significant contributions to the project as they learn the related elementary particle physics and electronics. During the construction phase of IceCube, a web site was created at the University of Delaware that provided an interface with local schools. The site will be updated to focus on science, particularly the near real time stream of data from the surface detectors along with an explanation of how these data trace solar activity and space weather.
