The recently completed IceCube neutrino observatory, located near the geographic South Pole, is collecting physics data in the largest instrumented volume of any neutrino detector. The complete IceCube detector instruments a full cubic kilometer of ice, including a densely spaced "DeepCore" component at the center of the detector. IceCube has the greatest sensitivity of any detector to astrophysical neutrinos at TeV - PeV energies. DeepCore extends IceCube's range to energies near 10 GeV where IceCube's large sample of atmospheric neutrinos is complementary to existing long baseline accelerator neutrino experiments. The next three years will see the exploitation of the full dataset of IceCube, with rich possibilities for neutrino physics and astrophysics.
This award continues support for the IceCube analysis group at the University of Alabama (UA) to explore cascade-based neutrino searches in the tau neutrino channel. At high energies, the tau channel is free of atmospheric neutrino background, making tau neutrino detection a "smoking gun" for an astrophysical source. The UA group will focus on combining the superior energy resolution of cascades with the unique waveforms and improved direction resolution of tau neutrinos. DeepCore will enhance the search for astrophysical tau neutrinos at energies down to 100 TeV where fluxes are expected to be higher and neutrinos can be observed from both hemispheres of the sky. At low energies around 25 GeV, where the tau neutrino appearance probability from atmospheric neutrino oscillation is maximal, the UA group will improve the directional and energy resolution of cascade reconstruction algorithms in order to search for the appearance of tau neutrino cascades in DeepCore.
Broader Impact: The University of Alabama is located in the diverse community of Tuscaloosa, and the university has a strong commitment to undergraduate and interdisciplinary research. The PI has developed an activity for high school students based on diffusion cloud chambers and has presented this activity to local physics and chemistry high school teachers through the UA Science in Motion Program. The PIs will continue to work with ASIM to bring high energy physics activities to the high school classroom. The UA Department of Physics and Astronomy has a strong public outreach program, and the PIs will continue public outreach activities at the UA campuses in Tuscaloosa and Birmingham.
Neutrinos are nearly massless subatomic particles that rarely interact with ordinary matter. These elusive cosmic messengers can provide clues to the origin of the highest energy cosmic ray particles and the nature of the most extreme astrophysical objects. In order to observe neutrinos from cosmic distances, a very large detector is required: IceCube, a cubic kilometer neutrino telescope located near the geographic South Pole. IceCube sensors are deployed between 1.5 and 2.5 kilometers deep in the Antarctic ice, and detect light from neutrinos interacting in the ice. The pattern of the light can be used to reconstruct the energy and direction of the neutrino. Detecting cosmic neutrinos also requires the elimination of "background" neutrinos which are produced in the Earth's atmosphere. The problem is analogous to attempting to see a faint star on a bright sunny day. Neutrinos come in three flavors: electron, muon and tau. The tau flavor is particularly interesting in searching for cosmic neutrinos because tau flavor neutrinos are rarely produced in the atmosphere and have much lower background than muon and electron neutrinos. This project focused on developing methods of detecting tau flavor neutrinos. A tau neutrino has a unique signature: when it interacts with the ice it produces a cascade of light from the interaction, and then a second cascade nearby from the decay of the tau lepton. This can produce a "double pulse" of light in the IceCube sensors. This project focused on determining how many double pulses can be expected from tau neutrinos in IceCube. The result of the project is that we can expect at least one double pulse from tau neutrinos (after background elimination) in the first three years of IceCube data, which will be available in 2014. Further studies are ongoing. This project has also focused on exposing the general public, K-12 and undergraduate students to the broader field of particle astrophysics. This project has supported demonstrations of a simple particle detector called a cloud chamber for local groups of female physics graduate and undergraduate students and postdoctoral researchers and faculty.
