TAUWER, a collaboration of Carnegie Mellon, Rome, and Turkey, uses the earth-skimming neutrino detection scheme initially proposed by Fargion in 1999-2001. TAUWER will implement it so as to provide an instrument of greater sensitivity, straight-forward expansion by an order of magnitude, and relatively low cost. TAUWER is a two-layer scintillator sampling telescope to detect the upward-moving air showers from tau hadronic decays. The hadronic decay channel of the tau-lepton makes possible a simple detection scheme based on identifying gammas, electrons and muons and determining their spatial density around the shower axis. Thus, detecting the showers from a set of tau-lepton decays gives a good estimate of the parent tau-neutrino spectrum. TAUWER is expandable, should future data indicate that need.
Previous work by this group has demonstrated that TAUWER detectors can separate upward and downward moving tracks by time of flight and to separate electrons and muons by waveform analysis after a Pb converter. This award provides funding to address the next crucial question in TAUWER validation - how well can one reject Extensive Air Shower (EAS) events in which independent particles hit the two scintillator tiles of a detector station and produce a signal that mimics the timing associated with an upward-moving shower particle? The three groups will work on building a library of tau-neutrino interactions and air shower development to use in building the multivariate likelihood scheme needed to go from shower profile and composition information back to parent neutrino energy and angle. Finally, there will be efforts to develop more cost-effective methods to handle the readout and waveform digitization. All these steps are crucial to the ultimate goal of constructing TAUWER as a premiere Neutrino Astronomy (NA) telescope to complement and extend the work now underway at IceCube and Auger.
Broader Impacts: Ultrahigh-energy cosmic neutrinos potentially open the way to understanding the acceleration mechanisms in Active Galactic Nuclei and other black-hole related sources distributed throughout the space-time continuum of our universe. The successful implementation and operation of TAUWER will have broad impact on black hole cosmology and on the fundamental question of the origin of the highest energy cosmic rays, one of the fundamental questions of our time.
One of the fundamental questions in modern astrophysics concerns the source of ultra-high energy cosmic rays (UHECR), particles that carry more than a million times the energy of protons at the world's highest energy particle accelerator in Switzerland. We do not understand the astrophysics of UHECR sources. It might be due to black holes. It might be due to supernovae. What we do know is that each potential acceleration source will be marked by the production of neutrinos whose energy spectrum labels the mechanism. The goal of the TAUWER experiment is to determine that energy spectrum in an energy range that complements measurements now being made at the South Pole by a variety of experiments. TAUWER uses a novel idea that depends on physics first observed in the 1990s - that neutrinos made by any strong interaction source associated with UHECR production will mix in the long, long travel distance to earth and appear here as equal fractions of the three known neutrino species. TAUWER is sensitive to the 1/3 of neutrinos that can interact in the earth and produce an outgoing particle, the tau lepton, whose decays can create observable clusters of particles in air. Ordinary cosmic ray interactions also occur in air, at rates that are enormously higher than these UHECR events. In order to become blind to these unwanted sources, TAUWER uses some special features of the tau lepton decays. In order to measure the effectiveness of these background rejection ideas and also to test some pioneering ideas on new electronics for cosmic ray experiments, this preliminary study of TAUWER detector design and background rate measurement from extensive air showers (EAS) was carried out with NSF support in tests done at the Karlsruhe EAS test facility, formerly the Kaskade-Grande EAS detector. The work was done by a small international collaboration featuring physicists from Carnegie Mellon (PI), University of Rome (La Sapienza), and Kars University and Abant Izzet Baysal University in Turkey. The TAUWER test used an array of eight detector stations and operated reliably year round for two years of data-taking, proving the robustness of the proposed detector design. The EAS events from the cosmic ray triggers were matched to event patterns in the test detector to see if there were any potential trigger candidates from this background. The rate was incredibly small, confirming the TAUWER design idea. The new hardware components had not been used before in the harsh operating conditions of a cosmic ray experiment. They proved to be stable and high-performance devices. Using these new elements will lower the cost of the full TAUWER detector by more than a factor of twenty compared to other operating experiments. Our pioneering work makes it clear to future experiment designers that these new devices can be successfully applied in large-scale cosmic ray experiments. In summary, the NSF support enabled us to verify and improve the TAUWER design, conduct extended operational tests of prototype devices, and develop simulations of signal events over a range of energy, location, and angle that we have used to evolve a full TAUWER reconstruction strategy. This was the purpose of the grant, and all objectives were achieved.
