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EUSO-SPB2 Cherenkov Telescope: Overview and First Neutrino Constraints

Tobias Heibges, Diksha Garg, Claire Guépin, Julia Burton-Heibges, John F. Krizmanic, Mary Hall Reno, Tonia M. Venters, Lawrence Wiencke

TL;DR

This work assesses the EUSO-SPB2 Cherenkov telescope's capability to detect Earth-skimming tau neutrinos via upward-going optical Cherenkov signals during a May 2023 balloon flight. By combining a bifocal optical design with stringent time-coincidence triggers, detailed data selection, and multiple detector models, the authors derive the first upper limits on the all-flavor diffuse neutrino flux from a balloon-borne optical Cherenkov configuration, illustrating the impact of clouds and detector modeling on sensitivity. Although the short flight yields limits that are not competitive with long-term experiments like IceCube, the analysis demonstrates a robust framework for future ToO searches and provides critical methodology for upcoming missions (PBR and POEMMA). The results establish the path for scaling up exposure and refining techniques in pursuit of transient neutrino sources with high-energy thresholds, informing design choices for next-generation balloon and satellite observatories.

Abstract

Earth-skimming tau neutrinos with energies above $\sim 10$ PeV can convert to tau leptons that decay in the atmosphere and initiate upward-going extensive air showers that generate optical Cherenkov signals. On a curtailed NASA balloon flight in May 2023, the Cherenkov telescope (CT) on the Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2) was launched and had a short flight at $\sim 30$ km altitude. With some time pointing below the Earth's limb, EUSO-SPB2 CT data allow searches for neutrino events that yield optical flashes from the forward-beamed Cherenkov light. We present an overview of the CT and provide upper limits for the diffuse astrophysical neutrino flux from flight data as a proof-of-principle demonstration. We also briefly describe how the methodology is extended to potential transient neutrino point sources.

EUSO-SPB2 Cherenkov Telescope: Overview and First Neutrino Constraints

TL;DR

This work assesses the EUSO-SPB2 Cherenkov telescope's capability to detect Earth-skimming tau neutrinos via upward-going optical Cherenkov signals during a May 2023 balloon flight. By combining a bifocal optical design with stringent time-coincidence triggers, detailed data selection, and multiple detector models, the authors derive the first upper limits on the all-flavor diffuse neutrino flux from a balloon-borne optical Cherenkov configuration, illustrating the impact of clouds and detector modeling on sensitivity. Although the short flight yields limits that are not competitive with long-term experiments like IceCube, the analysis demonstrates a robust framework for future ToO searches and provides critical methodology for upcoming missions (PBR and POEMMA). The results establish the path for scaling up exposure and refining techniques in pursuit of transient neutrino sources with high-energy thresholds, informing design choices for next-generation balloon and satellite observatories.

Abstract

Earth-skimming tau neutrinos with energies above PeV can convert to tau leptons that decay in the atmosphere and initiate upward-going extensive air showers that generate optical Cherenkov signals. On a curtailed NASA balloon flight in May 2023, the Cherenkov telescope (CT) on the Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2) was launched and had a short flight at km altitude. With some time pointing below the Earth's limb, EUSO-SPB2 CT data allow searches for neutrino events that yield optical flashes from the forward-beamed Cherenkov light. We present an overview of the CT and provide upper limits for the diffuse astrophysical neutrino flux from flight data as a proof-of-principle demonstration. We also briefly describe how the methodology is extended to potential transient neutrino point sources.

Paper Structure

This paper contains 4 sections, 1 equation, 4 figures.

Table of Contents

  1. Introduction
  2. Cherenkov telescope, data selection and simulation criteria
  3. Diffuse neutrino upper limits
  4. Transient neutrino sources and future prospects

Figures (4)

  • Figure 1: The red dashed line shows the balloon's altitude, while the green and orange lines indicate observations above and below the Earth's limb, respectively. The cloud area fraction below the EUSO-SPB2 flight path is shown as a function of altitude according to the color scale on the right.
  • Figure 2: Simulated bifocal trigger event made using the OffLine software package JEM-EUSO:2023fyg, neglecting camera electronics modeling, for a $5\times 10^9$ GeV EAS coming from 96$^\circ$ zenith angle (just below the Earth's limb, as seen from the balloon at 33 km), with the EAS starting after traveling 100 km distance in the atmosphere.
  • Figure 3: First, second and third columns show high-, mid-, and low-level cloud area fractions for Night 1 (top panel) and Night 2 (bottom panel). The red line indicates the balloon trajectory, and the yellow star indicates the time stamp of the cloud snapshot. The orange lines indicate the approximate FoV of the CT.
  • Figure 4: Left: Acceptances to diffuse $\nu_{\tau}$s as a function of energy for a 12.8$^\circ$ azimuthal FoV calculated using NuSpaceSim (blue), a simplified detector model (red), and a detailed detector model using the OffLine software (green). The solid lines represent calculations not accounting for cloud coverage, and the dashed lines represent calculations assuming clouds up to 2 km in altitude. Right: Corresponding per-decade all-flavor 90% unified confidence upper limits on the diffuse neutrino flux as functions of energy.