Unusual Near-Horizon Cosmic-Ray-like Events Observed by ANITA-IV

• Published in: Physical Review Letters
• Main Authors: Gorham, P., Ludwig, A., Deaconu, C., Cao, P., Allison, P., Banerjee, O., Batten, L., Bhattacharya, D., Beatty, J., Belov, K., Binns, W., Bugaev, V., Chen, C., Chen, P., Chen, Y., Clem, J., Cremonesi, L., Dailey, B., Dowkontt, P., Fox, B., Gordon, J., Hast, C., Hill, B., Hsu, S., Huang, J., Hughes, K., Hupe, R., Israel, M., Liu, T., Macchiarulo, L., Matsuno, S., McBride, K., Miki, C., Nam, J., Naudet, C., Nichol, R., Novikov, A., Oberla, E., Olmedo, M., Prechelt, R., Rauch, B., Roberts, J., Romero-Wolf, A., Rotter, B., Russell, J., Saltzberg, D., Seckel, D., Schoorlemmer, H., Shiao, J., Stafford, S., Stockham, J., Stockham, M., Strutt, B., Sutherland, M., Varner, G., Vieregg, A., Wang, S., Wissel, S.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2021
• Subjects: Antarctic; The Antarctic; Antarc*
• Online Access: http://hdl.handle.net/21.11116/0000-000A-33C4-F

ANITA's fourth long-duration balloon flight in 2016 detected 29 cosmic-ray (CR)-like events on a background of 0.37(-0.17)(+0.27) anthropogenic events. CRs arc mainly seen in reflection off the Antarctic ice sheets, creating a phase-inverted waveform polarity. However, four of the below-horizon CR-like events show anomalous noninverted polarity, a p = 5.3 x 10(-4) chance if due to background. All anomalous events are from locations near the horizon; ANITA-IV observed no steeply upcoming anomalous events similar to the two such events seen in prior flights.