Precision Ultra-High Energy Neutrino Astrophysics and New Signatures Enabled by a Complete Treatment of Birefringence in Antarctic Ice

Ohio State University, The, Columbus OH

Investigators

Abstract

Ultra-high energy (UHE) neutrinos with energies greater than 10^17 electronvolts are a key missing piece in the rapidly developing field of multi-messenger astrophysics. Their detection will prove essential in answering the century-old question of the nature of the most extreme astrophysical sources. Experiments employing radio techniques are amongst the most promising for measuring UHE neutrinos, where such event interactions occurring in natural ice environments result in detectable radio-frequency signals propagating over kilometer-scale distances. This award supports scientists at the Ohio State University performing research in the study of key ice parameters that directly impact the searches for the first detections of UHE neutrinos. The awarded program will leverage an interdisciplinary approach – spanning neutrino astrophysics, climate science, glaciology, remote sensing, evolutionary computation, and antenna engineering - to address the property of ice birefringence at the NSF’s Amundsen-Scott South Pole Station, Antarctica. Undergraduate researchers will play key roles in the interdisciplinary team, including leading the GENETIS project to assess the impact of birefringence on optimal designs of next-generation arrays for detecting UHE neutrinos. In addition, through the ASPIRE program, high school women will have the opportunity to gain first-hand research experiences. Quantifying the birefringence parameters (where the speed of a signal depends on its direction and polarization) in the ice is necessary to determine the local polarization where a radio signal is emitted in a neutrino interaction. A signal produced in the ice propagates as two rays that travel at different speeds. If the birefringence parameters are known, the time delay between the two rays would be a clear signature of a signal originating from within the ice, and provides a precise measure of the distance to the interaction necessary for the event energy reconstruction. Using pulser measurements taken with the deployed Askaryan Radio Array (ARA) at South Pole will provide the best fit depth-dependent parameters characterizing the ice birefringence. These parameters may then be incorporated into a complete ice model for detection of UHE neutrinos. Folding this information into the expected radio emission signatures will lower previous search thresholds and enhance the on-going search for the first detection of UHE neutrinos. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.