Background contributions in the electron-tracking Compton camera onboard SMILE-2+

TL;DR

This study assesses background contributions in the electron-tracking Compton camera on SMILE-2+ using Monte Carlo simulations, identifying key background sources and demonstrating background reduction techniques to enhance gamma-ray observation sensitivity.

Contribution

It provides a detailed analysis of background sources in the ETCC and demonstrates the effectiveness of Compton-kinematics tests in reducing background noise.

Findings

Background below 400 keV mainly from atmospheric gamma rays and cosmic rays.

Unresolved background component above 400 keV not related to direct Compton events.

Compton-kinematics test reduces background noise by an order of magnitude.

Abstract

The Mega electron volt (MeV) gamma-ray observation is a promising diagnostic tool for observing the universe. However, the sensitivity of MeV gamma-ray telescopes is limited due to peculiar backgrounds, restricting the application of MeV gamma rays for observation. Identification of backgrounds is crucial for designing next-generation telescopes. Therefore, herein, we assessed the background contribution in the electron-tracking Compton camera (ETCC) on board the SMILE- 2+ balloon experiment. This assessment was performed using the Monte Carlo simulation. The results revealed that the background below 400 keV existed due to the atmospheric gamma-ray background, the cosmic-ray/secondary-particle background, and the accidental background. On the other hand, the unresolved background component, which was not likely to be relevant to direct Compton-scattering events in the ETCC, was confirmed above 400 keV. Overall, this study demonstrated that the Compton-kinematics test provides a powerful tool to remove the background and principally improves the signal-to-noise ratio at 400 keV by an order of magnitude.