A Review of the EUSO-Balloon Pathfinder for the JEM-EUSO Program

Area of Science:

• Astrophysics
• Cosmic Ray Physics
• Space Science

Background:

• The JEM-EUSO mission aims to observe Ultra-High Energy Cosmic Rays (UHECRs) by detecting their induced Extensive Air Showers (EAS) via UV light from space.
• EUSO-Balloon served as a crucial pathfinder mission to test JEM-EUSO's core technologies in a near-space environment.

Purpose of the Study:

• To evaluate the performance of JEM-EUSO's key technologies during a stratospheric balloon flight.
• To gain insights into detector performance under various atmospheric conditions for future space missions.
• To measure diffuse UV light intensity and validate the detection of artificial EAS-like events.

Main Methods:

• A stratospheric balloon (EUSO-Balloon) was launched to an altitude of 38 km, carrying a UV detector sensitive to wavelengths of approximately 290-500 nm.
• The detector operated for over 5 hours, collecting data on photoelectron counts and imaging UV light.
• Simulations of instrument response and atmospheric models were used to estimate diffuse light intensity, and laser tracks mimicking EAS were detected and reconstructed.

Main Results:

• The EUSO-Balloon flight successfully demonstrated the functionality of key JEM-EUSO technologies.
• Detailed measurements of photoelectron counts were obtained under diverse atmospheric and ground conditions.
• Hundreds of laser tracks, simulating EAS, were detected and their direction reconstructed, marking the first such measurements from a downward-looking fluorescence detector.

Conclusions:

• The EUSO-Balloon mission provided valuable data and understanding for improving future space-based UHECR observatories.
• The successful detection and reconstruction of laser tracks validate the approach for observing EAS from space.
• Results inform the design and operational strategies for the upcoming JEM-EUSO mission.