The high-energy frontier has traditionally led to dramatic breakthroughs in our understanding of nature. However, the usual tools of astronomy have difficulties gathering the requisite information at the highest energies. The universe is opaque to light with energy above 1015 eV if originating from outside of our galactic neighborhood, and charged cosmic rays do not carry directional information because of their deflection by galactic magnetic fields. The AMANDA detector, completed in 2000, was the first to search for astrophysical neutrinos from sources in the northern sky. After 5 successful years of operation, it has now been incorporated into the IceCube, a new detector based on the AMANDA concept which is under construction at the South Pole. AMANDA was designed to explore the highest energy bands of astronomy based on the detection of the neutrino, a particle with properties that complement those of the photon and charged cosmic rays. At energies that overlap with mature fields of observational astronomy, multi-messenger astrophysics is possible. IceCube continues this quest but with several important improvements. Its energy resolution is expected to be good enough to confidently select neutrino events with energy between 1012-1015 eV. If the astrophysical neutrino signal is sufficiently strong to provide tens of events or more, IceCube will measure the energy spectrum, which is an important diagnostic when interpreting the data. As a precursor to detailed analysis of data from IceCube strings, we intend to develop a new technique to better estimate the energy of the neutrino using powerful, new capabilities of the recently-installed AMANDA Transient Waveform Recorders (TWR) data acquisition system. TWR provides a complete digital record of the output from every AMANDA sensor embedded in the ice. This beautifully complements the readout scheme of IceCube, which also plans to acquire digital records of detector signals, but with better fidelity.
Multi-messenger astronomy may be the most powerful method to decipher the physics of particle acceleration in Active Galaxies or GRBs (Gamma Ray Bursts), which have been identified as possible sources of the highest energy cosmic rays. As a particle physics experiment detecting neutrinos with energies far beyond those produced at terrestrial accelerators, IceCube has the potential to uncover new physics based on high energy collisions between neutrinos and ordinary matter. If GRBs emit a detectable flux of neutrinos, then the physics opportunities become even more exciting. For example, the weak equivalence principle can be tested by the contemporaneous measurement of the photon and neutrino arrival times.
Because of the fundamental similarity in the data records between IceCube and AMANDA, we propose to develop and verify the accuracy of a new energy estimator that utilizes the additional information provided by TWR data and adapt it to include IceCube strings as they are installed. We plan to use the energy information to provide more powerful tools to search for sources of high energy neutrinos and with luck, reveal the long-sought source of cosmic rays.
