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The Kavli Institute for Cosmological Physics at the University of Chicago Ice Geometry as Possible Explanation for Upgoing Cosmic Ray Showers Detected by ANITA Lily Liu INTRODUCTION ICE BRIDGE GEOMETRY SASTRUGI GEOMETRY ANALYSIS What are neutrinos? Finite-Difference Time-Domain (FDTD) Simulation Ice Bridge • Neutrinos are a fundamental particle that can be • We used MIT Electromagnetic Equation Propagation • Pulse traveling through the ice will reflect off the air produced in the universe through interactions between (MEEP) simulation software, which simulates without inverting polarity and with reasonable signal-to- cosmic rays and the cosmic microwave background electromagnetic systems in a discrete grid with Maxwell’s noise ratio • These neutrinos are capable of traveling billions of light Equations • It is possible that the pulse detected by ANITA was years on paths that are not bent by intergalactic magnetic • The pulse was created using an interpolation function with actually from a cosmic ray event that reflected off the air fields a previously simulated cosmic ray event pulse rather than off the ice • Ultrahigh-energy neutrinos can reveal valuable Sastrugi information about how particles interact at the highest n=1.35 Reflection of pulse off of flat ice. • Quickly changing slopes affect the reflection of the pulse, possible energies Reflection of pulse off of ice with sastrugi leading to a more ambiguous pulse shape • When the pulse reflected at a valley between two ANtarctic Impulsive Transient Antenna (ANITA) n=1 sastrugi, it was very difficult to determine the polarity of • ANITA is a balloon experiment that flies 40km above the reflected pulse n=1.35 Antarctica • The events detected by ANITA are also accompanied by • Ultrahigh-energy neutrinos that interact in the ice generate n=1 thermal noise and other radio frequency noise particle showers through Askaryan radiation disturbances. Ambiguous pulse shape and complex n=1.35 • Tau neutrinos can interact through a charged current interfering noise could cause an inverted pulse to appear interaction, generating a particle shower from the A simulated ice bridge. The red indicates negative electric field and non-inverted subsequent tau lepton decay the blue indicates positive electric field. The pulse is emitted from the green dot in the upper left corner, and we took measurements of • Cosmic rays can interact in the atmosphere and induce electric field at the orange dot. particle showers that are detected directly • Reflected cosmic rays interact in the atmosphere and induce a particle shower that is reflected off the ice and detected with inverted polarity • Sources of background noise include thermal, anthropogenic, and satellite noise Electric field from reflection off flat ice as measured at orange dot. First pulse is from original pulse emitted by the source, and second pulse is from reflection off the ice – clear inverted polarity. Proposed tau-neutrino explanation Other Theories • Tau neutrinos, sterile neutrinos, and transition radiation Reflections of pulse off ice bridge, as measured at the orange dot shown above. • However, these are in contradiction with standard neutrino- matter interaction models and with the current best EeV • First pulse: original pulse emitted by the source diffuse neutrino flux limits set by the Pierre Auger Observatory, the IceCube neutrino detector, and ANITA • Second pulse: reflection off the ice – inverted polarity • Third pulse: refraction through ice and subsequent reflection off air layer – non-inverted Acknowledgements: Thank you to Professor Abigail Vieregg Diagram of ANITA, showing the four impulsive events and Andrew Ludwig for their help and guidance throughout this • Fourth pulse: refraction through the ice and air layers and that can be detected. Background noise is also shown, project. with the exception of thermal noise. reflection off the bottom layer of ice – inverted polarity Electric field from reflection off sastrugi – ambiguous polarity. References: The Vieregg Lab [1] Radio Detection of High Energy Neutrinos, A. Connolly and A. Vieregg, July 2016 [4] Observation of an Unusual Upward-going CosMic-ray-like Event in [2] A Technique for Detection of PeV Neutrinos, A. Vieregg et. al., January 2016 the Third Flight of ANITA, P. W. GorhaM et al., March 2018 [3] Characteristics of Four Upward-Pointing CosMic-Ray-like Events Observed with https://kicp.uchicago.edu/~avieregg/ ANITA, P. W. GorhaM et al., PRL, August 2016.

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