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Observational Constraints on the Ultra-high Energy Cosmic Neutrino Flux from the Second Flight of the ANITA Experiment

The ANITA Collaboration, P. W. Gorham, P. Allison, B. M. Baughman, J. J. Beatty, K. Belov, D. Z. Besson, S. Bevan, W. R. Binns, C. Chen, P. Chen, J. M. Clem, A. Connolly, M. Detrixhe, D. De Marco, P. F. Dowkontt, M. DuVernois, E. W. Grashorn, B. Hill, S. Hoover, M. Huang, M. H. Israel, A. Javaid, K. M. Liewer, S. Matsuno, B. C. Mercurio, C. Miki, M. Mottram, J. Nam, R. J. Nichol, K. Palladino, A. Romero-Wolf, L. Ruckman, D. Saltzberg, D. Seckel, G. S. Varner, A. G. Vieregg, Y. Wang

TL;DR

This work reports ANITA-II's observational constraints on the ultra-high-energy cosmic neutrino flux from a 28.5-day balloon flight, detailing instrumental upgrades, calibration, and a rigorous blind analysis to estimate backgrounds. Two potential neutrino-like events survive in the Vpol channel, while three Hpol events align with UHECR geo-synchrotron expectations, leading to a strong 90% CL integral flux limit of Eν^2Fν ≤ 2×10^-7 GeV cm^-2 s^-1 sr^-1 over 10^18–10^23.5 eV, excluding several cosmogenic neutrino models and refining boundaries on UHECR source theories. The results demonstrate the viability of radio-detection techniques for cosmic neutrinos and set the stage for future improvements in background suppression and sensitivity.

Abstract

The Antarctic Impulsive Transient Antenna (ANITA) completed its second long-duration balloon flight in January 2009, with 31 days aloft (28.5 live days) over Antarctica. ANITA searches for impulsive coherent radio Cherenkov emission from 200 to 1200 MHz, arising from the Askaryan charge excess in ultra-high energy neutrino-induced cascades within Antarctic ice. This flight included significant improvements over the first flight in the payload sensitivity, efficiency, and a flight trajectory over deeper ice. Analysis of in-flight calibration pulses from surface and sub-surface locations verifies the expected sensitivity. In a blind analysis, we find 2 surviving events on a background, mostly anthropogenic, of 0.97+-0.42 events. We set the strongest limit to date for 1-1000 EeV cosmic neutrinos, excluding several current cosmogenic neutrino models.

Observational Constraints on the Ultra-high Energy Cosmic Neutrino Flux from the Second Flight of the ANITA Experiment

TL;DR

This work reports ANITA-II's observational constraints on the ultra-high-energy cosmic neutrino flux from a 28.5-day balloon flight, detailing instrumental upgrades, calibration, and a rigorous blind analysis to estimate backgrounds. Two potential neutrino-like events survive in the Vpol channel, while three Hpol events align with UHECR geo-synchrotron expectations, leading to a strong 90% CL integral flux limit of Eν^2Fν ≤ 2×10^-7 GeV cm^-2 s^-1 sr^-1 over 10^18–10^23.5 eV, excluding several cosmogenic neutrino models and refining boundaries on UHECR source theories. The results demonstrate the viability of radio-detection techniques for cosmic neutrinos and set the stage for future improvements in background suppression and sensitivity.

Abstract

The Antarctic Impulsive Transient Antenna (ANITA) completed its second long-duration balloon flight in January 2009, with 31 days aloft (28.5 live days) over Antarctica. ANITA searches for impulsive coherent radio Cherenkov emission from 200 to 1200 MHz, arising from the Askaryan charge excess in ultra-high energy neutrino-induced cascades within Antarctic ice. This flight included significant improvements over the first flight in the payload sensitivity, efficiency, and a flight trajectory over deeper ice. Analysis of in-flight calibration pulses from surface and sub-surface locations verifies the expected sensitivity. In a blind analysis, we find 2 surviving events on a background, mostly anthropogenic, of 0.97+-0.42 events. We set the strongest limit to date for 1-1000 EeV cosmic neutrinos, excluding several current cosmogenic neutrino models.

Paper Structure

This paper contains 6 sections, 5 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Experimental Technique
  3. Data Analysis
  4. Results
  5. Discussion
  6. Acknowledgments

Figures (5)

  • Figure 1: The ANITA-II payload on ascent with the lower eight horn antennas deployed. The payload height is $\sim$8 meters, and each antenna face is 0.95 m across. The inset shows the balloon and payload viewed telescopically at float altitude of 35 km.
  • Figure 2: The vertical-polarization reconstruction position of all 21.2 M Quality Events, with the color scale representing the average peak value of the interferometric image for events which fall in that bin. The dark blue region is consistent with pure thermal noise. The green, yellow, and red regions are increasingly non-thermal and are consistent with anthropogenic noise.
  • Figure 3: Events remaining after unblinding. The Vpol neutrino channel contains two surviving events. Three candidate UHECR events remain in the Hpol channel. Ice depths are from BEDMAP BEDMAP.
  • Figure 4:
  • Figure 5: ANITA-II limit for 28.5 days livetime. The red curve is the expected limit before unblinding, based on seeing a number of candidates equal to the background estimate. The blue curve is the actual limit, based on the two surviving candidates. Other limits are from AMANDA AMANDA08, RICE RICE06, Auger Auger07, HiRes Hires08, and a revised limit from ANITA-I hooverThesis. The BZ (GZK) neutrino model range is determined by a variety of models PJ96Engel01Kal02Kal02aAramo05Ave05Barger06.