Multiclass Search for Cosmic Ultra-High Energy Neutrinos with ANITA-IV

Abstract

The Antarctic Impulsive Transient Antenna (ANITA) is a balloon-borne experiment that suspends over the Antarctic ice sheet to detect upcoming radio pulses. Its goal is to see radio pulses originating from a rare interaction between Ultra-High Energy (UHE) neutrinos and ice to produce a shower of charged particles. The electromagnetic radiation produced from this shower is known as Askaryan radiation. The sensitivity at which ANITA needs to detect these events means most of the data ANITA collects is background. This background comes from multiple sources, from natural sources like the sun and electromagnetic discharge aboard the instrumentation to anthropogenic sources like satellites and research base communication. Also collected by ANITA are signals associated with radiation from charged particle showers produced in the air interacting with the Earth's magnetic field. In contrast to the radio pulses in the ice that are expected to be vertically polarized, these events are found to be horizontally polarized. Past analyses have focused on designing final cuts to remove thermal background, considering it to dominate over other types of background. However, after selecting events that look most like signals of interest, I estimate an upper limit to how many of them could be misclassified background. My exploratory analysis found 33 events, with 32 estimated as belonging to classes with horizontal polarization and one with vertical polarization.